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Microbiology and Parasitology for nutrition students undertaking diploma or degrees in Nutrition and dietetic.

Microbiology and Parasitology for nutrition students undertaking diploma or degrees in Nutrition and dietetic.



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  • 19/6/2013 nutrition student lecture. <br /> This lecture elaborates how microbes grow and spoil the food. <br />
  • Algal toxins are of importance as far as fish and crustacean are concerned. <br />
  • Radiation as a mode of food preservation. <br />
  • VERY IMPORTAN INFORMATION ON RADIATION RESISTANT ORGANISMS <br /> REF:Modern Food Microbiology <br /> Sixth Edition <br /> James M. Jay <br /> Professor Emeritus <br /> Wayne State University <br /> Detroit, Michigan <br /> Adjunct Professor <br /> University of Nevada Las Vegas <br /> Las Vegas, Nevada <br />
  • The latter pass <br /> out of the bowel in feces. When sporocysts are <br /> ingested by pigs or bovines, the sporozoites are <br /> released and spread throughout the body. They <br /> multiply asexually and lead to the formation of <br /> sarcocysts in skeletal and cardiac muscles. <br />
  • About 80% of the zygotes form thick-walled oocysts that sporulate within host cells.The environmentally resistant oocysts are shed in feces, and the infection is transmitted to other hosts when they are ingested. <br />
  • The disease is <br /> self-limiting, with an incubation period of 6-14 <br /> days, and symptoms typically last 9-23 days. In <br /> the immunocompromised, diarrhea is profuse <br /> and watery, with as many as 71 stools per day <br /> and up to 17 liters per day reported.29 Diarrhea <br /> is sometimes accompanied by mucus but rarely <br /> blood. Abdominal pain, nausea, vomiting and <br /> low-grade (less than 39°C) fever are less frequent <br /> than diarrhea, and symptoms may last for more <br /> than 30 days in the immunocompromised but <br /> generally less than 20 days (range: 4-21 days) <br /> in the immunocompetent. <br />
  • and the genera discussed in this <br /> chapter belong to two classes: <br /> Phylum Platyhelminthes <br /> Class Trematoda (flukes) <br /> Subclass Digenea <br /> Order Echinostomata <br /> Family Fasciolidae <br /> Genus FascioIa <br /> Genus Fasciolopsis <br /> Order Plagiorchiata <br /> Family Troglotrematidae <br /> Genus Paragonimus <br /> Order Opisthorchiata <br /> Family Opisthorchiidae <br /> Genus Clonorchis <br /> Class Cestoidea <br /> Subclass Eucestoda (tapeworms) <br /> Order Pseudophyllidea <br /> Family Diphyllobothriidae <br /> Genus Diphyllobothrium <br /> Order Cyclophyllidea <br /> Family Taeniidae <br /> Genus Taenia <br />
  • they, along with humans, are its principal <br /> definitive hosts. <br /> This parasite matures in the bile ducts, and <br /> the large operculate eggs (150 x 90 um in size) <br /> enter the alimentary tract from bile ducts and <br /> eventually exit the host in feces. After a period <br /> of 4-15 days in water, the miricidium develops, <br /> enters a snail, and is transformed into a sporocyst. <br /> The sprocyst produces mother rediae, which <br /> later become daughter rediae and cercariae. <br /> When the cercariae escape from the snail, they <br /> become free swimming, attach to grasses and <br /> watercress, and encyst to form metacercariae. <br /> When ingested by a definitive host, the metacercariae <br /> excyst in the duodenum, pass through the <br /> intestinal wall, and enter the coelomic cavity. <br /> From the body cavity, they enter the liver, feed <br /> on its cells, and establish themselves in bile ducts, <br /> where they mature.1873 <br /> Fascioliasis in cattle and sheep is a serious <br /> economic problem that results in the condemnation <br /> of livers. Human cases are known, especially <br /> in France, and they are contracted from raw or <br /> improperly cooked watercress that contains attached <br /> metacercariae. <br />
  • The disease <br /> is accompanied typically by eosinophilia. Fascioliasis <br /> can be diagnosed by demonstrating eggs <br /> in stools or biliary or duodenal fluids. Effective <br /> treatment is achieved upon the administration of <br /> praziquantel.73 <br />
  • Unlike E hepatica, <br /> this parasite occurs in the duodenum andjejunum <br /> of humans and pigs, and human infection rates <br /> as high as 40% are found in parts of Thailand, <br /> where certain uncooked aquatic plants are <br /> eaten.18 <br />
  • Death may <br /> occur in extreme cases.73 Symptoms appear to <br /> be due to the general toxic effect of metabolic <br /> products of the flukes. <br /> Diagnosis is made by demonstrating eggs in <br /> stools. The eggs of E buski are 130-140 urn by <br /> 80-85 um in size. Both niclosamide and praziquantel <br /> are effective in treating this disease.73 <br />
  • It is found primarily in <br /> Asia but also in Africa and South and Central <br /> America. P. kellicotti is found in North and Central <br /> America. In contrast to the trematodes, P. <br /> westermani is a lung fluke. <br /> The eggs of this parasite are expelled in sputum <br /> from definitive hosts (humans and other <br /> animals), and the miricida develop in 3 weeks in <br /> moist environments. A miricidium penetrates a <br /> snail (first intermediate host) and later gives rise <br /> to daughter rediae and cercariae about 78 days <br /> after entering the snail.18 The cercariae enter a <br /> second intermediate host (crab or crayfish) and <br /> encyst. The crustacean host in parts of the Orient <br /> and the Philippines are various species of <br /> freshwater crabs, where they usually form metacercarial <br /> cysts in leg and tail muscle.73 In P. <br /> kellicotti, cysts form in the heart region.73 When <br /> the definitive host ingests the infected crustacean, <br /> the metacercariae hatch out oftheir shells, <br /> bore their way as young flukes through the walls <br /> of the duodenum, and then move to the lungs, <br /> where they become enclosed in connective tissue <br /> cysts.73 The golden-brown eggs may appear <br /> in sputum 2-3 months later. <br /> Symptoms,Diagnosis, and Treatment <br /> Paragonimiasis is accompanied by severe <br /> chronic coughing and sharp chest pains. Sputum <br /> is often reddish-brown or bloody. Other nonspecific <br /> symptoms may occur when parasites <br /> lose their way to the lungs.73 Diagnosis is made <br /> by demonstrating the golden-brown eggs in sputum <br /> or stools. The eggs of P. westermani are <br /> 80-120 jum in length and 50-60 um in width. <br /> Also, a complement fixation test titer of at least <br /> 1:16 is diagnostic, and ELISA tests are available. <br /> The disease can be treated with praziquantel.73 <br />
  • When humans consume fish flesh that contains <br /> plerocercoid larvae, the larvae attach to the <br /> ileal mucosa by two adhesive grooves (bothria) <br /> on each scolex and develop in 3-4 weeks into <br /> mature forms. As a worm matures, its strobila, <br /> made up of proglottids, increases in length to <br /> 10 m or nearly 20 m, and each worm may produce <br /> 3,000-4,000 proglottids that are wider than <br /> they are long (hence, broad fish tape) (see Figure <br /> 29-1). Over 1 million eggs may be released <br /> each day into stools of victims. Eggs are more <br /> often seen in stools than proglottids, and they <br /> are not infective for humans. <br /> When human feces are deposited in waters, <br /> the eggs hatch and release six-hooked, freeswimming <br /> larvae or coracidia (also known as <br /> oncospheres). When these forms invade small <br /> crustaceans (copepods or microcrustaceans such <br /> as Cyclops orDiaphtomus), they metamorphose <br /> into a juvenile stage designated metacestode or <br /> procercoid larvae. When a fish ingests the crustacean, <br /> the larvae migrate into its muscles and <br /> develop into plerocercoid larvae. If this fish is <br /> eaten by a larger fish, the plerocercoid migrates, <br /> but it does not undergo further development. <br /> Humans are infected when they eat fish containing <br /> these forms. <br />
  • One of the consequences <br /> of this infestation is a vitamin B-12 deficiency, <br /> along with macrocytic anemia. <br /> This disease is diagnosed by demonstrating <br /> eggs in stools. Treatment is the same as for taeniasis. <br /> The absence of overt symptoms does not <br /> mean the absence of the tapeworm in the intestines <br /> because the worms may persist for many <br /> years. <br />
  • They are unique among both <br /> flatworm and roundworm parasites in that humans <br /> are their definitive hosts; the adult and <br /> sexually mature stages develop in humans, <br /> whereas the larval orjuvenile stage develops in <br /> herbivores. These helminths have no vascular, <br /> respiratory, or digestive systems nor do they possess <br /> a body cavity. They depend on the digestive <br /> activities of their human hosts for all of their <br /> nourishment. <br />
  • The latter increase in length, with the <br /> oldest being the farthest away from the scolex. <br /> Each proglottid has a complete set of reproductive <br /> organs, and an adult worm may contain up <br /> to 2,000 proglottids. These organisms may live <br /> up to 25 years and grow to a length of 4-6 m <br /> inside the intestinal tract. T. saginata sheds <br /> 8-9 proglottids daily, each containing 80,000 <br /> eggs. The eggs are not infective for humans. <br /> When proglottids reach soil, they release their <br /> eggs, which are 30-40 urn in diameter, contain <br />
  • Cysticercosis is the term used to designate the <br /> existence of these parasites in the intermediate <br /> hosts. The cysticerci usually take 2 or 3 months <br /> to develop after eggs are ingested by a herbivore. <br /> When present in large numbers, the cysticerci <br /> impart a spotted appearance to the beef <br /> issue. Humans become infected upon the ingestion <br /> of meat that contains cysticerci. <br /> The infection caused by the pork tape (T. <br /> solium) is highly similar to that described for the <br /> beef tape, but there are some significant differences. <br /> Although humans are also the definitive <br /> hosts, the larval stages develop in both swine and <br /> humans. In other words, humans can serve as <br /> intermediate (cysticercosis) and definitive (taeniasis) <br /> hosts, thus making autoinfections possible. <br /> For this reason, T. solium infections are <br /> potentially more dangerous than those of <br /> T. saginata. The infection caused by larval forms <br /> of T. solium is sometimes designated Cysticercus <br /> cellulosae. The T. solium scolex has hooks <br /> rather than sucking discs, and the strobila may <br /> reach 2-4 m and contain only about 1,000 proglottids. <br /> Embryos of T. solium are carried to all <br /> tissues of the body, including the eyes and brain <br /> in contrast to T. saginata. <br />
  • In these cysticercosis cases, the cysticerci <br /> develop in body tissues, including those ofthe <br /> central nervous system, and generally lead to <br /> eosinophilia. <br /> Human taeniasis is diagnosed by demonstration <br /> of eggs or proglottids in stools and cysticercosis <br /> by tissue biopsies of calcified cysticerci or <br /> by immunological methods. Complement fixation, <br /> indirect hemagglutination, and immunofluorescence <br /> tests are valuable diagnostic aids. <br /> A single-dose oral treatment with niclosamide, <br /> which acts directly on the parasites, is effective <br /> in ridding the body of adult worms. This drug <br /> apparently inhibits a phosphorylation reaction in <br /> the worm&apos;s mitochondria. Another effective chemotherapeutic <br /> agent is praziquantel. With cysticercosis, <br /> surgery may be indicated. <br /> Prevention <br /> The general approach in the prevention and <br /> elimination of diseases that require multiple hosts <br /> is to cut the cycle of transmission from one host <br /> to another. Because the eggs are shed in human <br /> feces, taeniasis can be eliminated by the proper <br /> disposal of sewage and human wastes, although <br /> T. solium infections in humans present a more <br /> complex problem. Cysticerci can be destroyed <br /> in beef and pork by cooking to a temperature of <br /> at least 600C.47 The freezing of meats to at least <br /> -100C for 10-15 days or immersion in concentrated <br /> salt solutions for up to 3 weeks will inactivate <br /> these parasites. Freezing times and temperatures <br /> necessary to ensure the death of all <br /> cysticerci from infected calves were found by <br /> one group to be as follows: 360 hours at -50C, <br /> 216 hours at -100C, and 144 hours at -15°C, <br /> -20°C,-25°C, or-300C.41 <br />
  • Genus Turbatrix <br /> Order Ascaridida <br /> GevmsAscaris <br /> Subfamily Anisakinae <br /> Genus Anisakis <br /> Genus Pseudoterranova <br /> (Phocanema) <br /> Genus Toxocara <br />
  • The eggs hatch <br /> within female worms, and each female can produce <br /> around 1,500. These larvae, each about <br /> 0.1 mm in length, burrow though the gut wall <br /> and pass throughout the body, ultimately lodging <br /> in certain muscles. Only those that enter skeletal <br /> muscles live and grow; the others are destroyed. <br /> The specific muscles affected include <br /> those of the eye, tongue, and diaphragm. <br />
  • The larvae grow <br /> to about 1 mm in muscles and then encyst by <br /> curling up and becoming enclosed in a calcified <br /> wall some 6-18 months later (Figure 29-2). The <br /> larvae develop no further until consumed by another <br /> animal (including humans), but they may <br /> remain viable for up to 10 years in a living host. <br /> When the encysted flesh is ingested by a second <br /> host, the encysted larvae are freed by the enzymatic <br /> activities in the stomach, and they mature <br /> in the lumen of the intestines. <br />
  • When only a few larvae are ingested, the incubation period may be as long as 30 days. The symptoms may <br /> persist for several days, or they may abate and <br /> be overlooked. The larvae begin to invade striated <br /> muscles about 7-9 days after the initial <br /> symptoms. Where 10 or fewer larvae are deposited <br /> per gram of muscle tissue, there are usually <br /> no symptoms. When 100 or more per gram are <br /> deposited, symptoms of clinical trichinosis usually <br /> develop, whereas for 1,000 or more per gram <br /> of tissue, serious and acute consequences may <br /> occur. Muscle pain (myalgia) is the universal <br /> symptom of muscle involvement, and difficulty <br /> in breathing, chewing, and swallowing may occur. <br /> 64 About 6 weeks after the initial infection, <br /> encystment occurs, accompanied by tissue pain, <br /> swelling, and fever. Resistance to reinfection <br /> develops, and it appears to be T cell mediated. <br /> Thiabendazole and mebendazole have been <br /> shown to be effective drugs for this disease. <br />
  • The <br /> feeding of uncooked garbage to swine helps to <br /> perpetuate this disease. Where only cooked garbage <br /> is fed to pigs, the incidence of trichinosis <br /> has been shown to fall sharply. <br /> This disease can be prevented by the thorough <br /> cooking of meats such as pork or bear meat. <br />


  • Food microbiology • Food microbiology is the study of the microorganisms that inhabit, create, or contaminate food and the study of microorganisms causing food spoilage. • What is the importance of food microbiology? • To study microorganism causing food spoilage,fermentation,and yeast production essention in food production WALTER WAKHUNGU WASWA 9
  • • What is Microbiology? • Microbiology is the study of microorganisms, that exist as single cells or cell clusters; it also includes viruses, which are microscopic but not cellular. • Parasite • Living organism that live in or on a host that provide physical protection and nourishment.term usually applied to protozoans and helminths • What is Parasitology? WALTER WAKHUNGU WASWA 10
  • Roles of microorganisms found in food  Spoilage, fermentation, food production.  Microorganisms are used in brewing, winemaking, baking, pickling and other food -making processes.  They are also used to control the fermentation process in the production of cultured dairy products such as yogurt and cheese. The cultures also provide flavour and aroma, and inhibit undesirable organisms.  Do you think bacteria can be consumed as prophylactic measures? WALTER WAKHUNGU WASWA 11
  • Primary sources of microorganisms 1. 2. 3. 4. 5. 6. 7. 8. Soil and water Plant and plant products Food utensils Git of animals and humans Food handlers Animal hides Air and dust Animal feeds WALTER WAKHUNGU WASWA 12
  • Primary source of food poisoning bacteria WALTER WAKHUNGU WASWA 13
  • Synopsis of common food borne bacteria • A synopsis is provided to give you a glimpse of what we are going to encounter in the course of our study. WALTER WAKHUNGU WASWA 14
  • Synopses of Genera of Moulds common to food • assignment1 WALTER WAKHUNGU WASWA 16
  • Synopsis of Genera of Yeasts common to foods • Assignment2 WALTER WAKHUNGU WASWA 17
  • Synopsis of mould • Molds are filamentous fungi that grow in the form of a tangled mass that spreads rapidly and may cover several inches of area in 2 to 3 days. • The total of the mass or any large portion of it is referred to as mycelium. Mycelium is composed of branches or filaments referred to as hyphae. • Those of greatest importance in foods multiply by ascospores, zygospores, or conidia. WALTER WAKHUNGU WASWA 18
  • cont • • • • • • • • • Aspergillus Aureobasidium (Pullularid). Botrytis. Byssochlamys. Cladosporium Colletotrichum. Fusarium. Penicillium Rhizopus. WALTER WAKHUNGU WASWA 19
  • SYNOPSIS OF COMMON GENERA OF FOODBORNE YEASTS Yeasts may be viewed as being unicellular fungi in contrast to the molds, which are multicellular; Some yeast produce mycelia to varying degrees. Yeasts can be differentiated from bacteria by their larger cell size and their oval, elongate, elliptical,or spherical cell shapes. WALTER WAKHUNGU WASWA 20
  • Genus: Brettanomyces Candida Cryptococcus Rhodotorula Trichosporon WALTER WAKHUNGU WASWA 21
  • The Causes of Food Spoilage • INTRINSIC PARAMETERS • This are parameters of plant and animal tissues that are an inherent part of the tissues . • These parameters are as follows: • pH • Moisture content • Oxidation-reduction potential (Eh) • Nutrient content • Antimicrobial constituents • Biological structures WALTER WAKHUNGU WASWA 22
  • Conditions for Spoilage •Water •pH •Physical structure •Oxygen •temperature WALTER WAKHUNGU WASWA 23
  • Microorganism Growth in Foods WALTER WAKHUNGU WASWA 24
  • Composition and pH • putrefaction – proteolysis and anaerobic breakdown of proteins, yielding foul-smelling amine compounds • pH impacts make up of microbial community and therefore types of chemical reactions that occur when microbes grow in food WALTER WAKHUNGU WASWA 25
  • Water availability • in general, lower water activity inhibits microbial growth • water activity lowered by: – drying – addition of salt or sugar • osmophilic microorganisms – prefer high osmotic pressure • xerophilic microorganisms – prefer low water activity WALTER WAKHUNGU WASWA 26
  • Physical structure • grinding and mixing increase surface area and distribute microbes – promotes microbial growth • outer skin of vegetables and fruits slows microbial growth WALTER WAKHUNGU WASWA 27
  • Antimicrobial substances • coumarins – fruits and vegetables • lysozyme – cow’s milk and eggs • aldehydic and phenolic compounds – herbs and spices • allicin – garlic • polyphenols – green and black teas WALTER WAKHUNGU WASWA 28
  • Extrinsic parameters • These are those properties of storage environment that affect both the foods and their microorganisms. 1.temperature I. lower temperatures retard microbial growth 2.relative humidity I. higher levels promote microbial growth 3.atmosphere I. oxygen promotes growth II. modified atmosphere packaging (MAP) III. use of shrink wrap and vacuum technologies to WALTER WAKHUNGU WASWA package food in controlled atmospheres 29
  • Incidence and types of microorganisms in food Fresh meat and poultry • Primary sources and routes of microorganisms • 1.stick knife • 2.animal hide • 3.git • 4.hands of handlers • 5.containers • 6.handling and storage environment • 7.Lymph nodes WALTER WAKHUNGU WASWA 30
  • Extended ground meat WALTER WAKHUNGU WASWA 31
  • • EXTENDED by addition of soy flour and frozen • Ie chicken soy blend • However bacteria grow faster in meat soy blend meat than non extended WALTER WAKHUNGU WASWA 32
  • • Ground meat or comminuted meat • Higher level of contamination. – Higher surface area – Meat grinders, cutting knives, storage utensils – One heavily contaminated meat portion ie lymph node • Bacteria – Bacilli and – Clostridium botulinum,perfringens,JEJUNII – E.coli – S.aureus – Klebsella pneumoniae,Enterobacter cloacae WALTER WAKHUNGU WASWA 33
  • • Mechanically deboned meat WALTER WAKHUNGU WASWA 34
  • • • • • By machines Less contact by man Which bacterial group is minimized? Coliforms WALTER WAKHUNGU WASWA 35
  • Hot boned meat • Processing meat 1-2 hrs after slaughter while carcass is still hot(pre rigor) • COLD BONED MEAT? • Mesophiles elevated WALTER WAKHUNGU WASWA 36
  • • Organ and variety meat WALTER WAKHUNGU WASWA 37
  • • Liver kidney hearts tongues • Higher ph and glycogen levels WALTER WAKHUNGU WASWA 38
  • • Vaccuum packaged meat WALTER WAKHUNGU WASWA 39
  • • Anaerobic bacteria will survive WALTER WAKHUNGU WASWA 40
  • • • • • Storage of various meat products Bacon Sausage bologna WALTER WAKHUNGU WASWA 41
  • • poultry WALTER WAKHUNGU WASWA 42
  • • vegetables WALTER WAKHUNGU WASWA 44
  • • Delicatessen WALTER WAKHUNGU WASWA 45
  • • Frozen meat pie WALTER WAKHUNGU WASWA 46
  • • Dehydrated foods WALTER WAKHUNGU WASWA 47
  • Microbial Growth and Food Spoilage • food spoilage – results from growth of microbes in food • alters food visibly and in other ways, rendering it unsuitable for consumption – involves predictable succession of microbes – different foods undergo different types of spoilage processes – toxins are sometimes produced • algal toxins may contaminate shellfish and finfish WALTER WAKHUNGU WASWA 48
  • Food Spoilage •Approximately 1/3rd of all food manufactured in world is lost to spoilage •Microbial content of foods (microbial load): qualitative (which bugs) and quantitative (how many bugs) •Shelf life •Non-perishable foods (pasta) •Semiperishable foods (bread) •Perishable foods (eggs) WALTER WAKHUNGU WASWA 50
  • Minimize contamination by: 1. Good management processes 2. Acceptable sanitary practices 3. Rapid movement of food through processing plant 4. Well-tested preservation procedures WALTER WAKHUNGU WASWA 51
  • Source Common Food Spoilage •Meat •Cutting board contamination •Conveyor belts •Temperature •Failure to distribute quickly •Fecal bacteria from intestines •Fish •Polluted waters •Transportation boxes WALTER WAKHUNGU WASWA 52
  • Cont…… •Poultry and Eggs •Human contact •Penetration by bacteria •Milk and Dairy Products •Lactobacillus and Streptococcus species that survive pasturization (sour milk) •Breads •Spores and fungi that survive baking •Grains •Fungi produce toxins WALTER WAKHUNGU WASWA 53
  • >>>>Food Microbiology • Foodborne Illnesses – Due to consumption of spoiled foods or foods containg harmful microbes or their products – Two categories of food poisoning • Food infections – Consumption of living microorganisms • Food intoxications – Consumption of microbial toxins rather than the microbe – Symptoms include nausea, vomiting, diarrhea, fever, fatigue, and muscle cramps WALTER WAKHUNGU WASWA 54
  • Preventing Foodborne Disease •Food infections (microbes are transferred to consumer) •Food poisoning (results from the toxin consumption) WALTER WAKHUNGU WASWA 55
  • FOOD POISONING 1. Food intoxication: Illness is caused by ingestion of food with • preformed toxin. Examples of food intoxication • Bacillus cereus 1-6 hours Vomiting, cramp Rice, Pasta dishes • Staphylococcus aureus 2-4 hours Vomiting Meat, Salads • Clostridium botulinum 12-72 hours Flaccid paralysis Meat, Vegetables WALTER WAKHUNGU WASWA 57
  • 2. Food infection: Illness is caused by ingestion of food with microorganism. • Incubation period and severity of disease in food infection is determined by inoculum of micro-organism ingested. WALTER WAKHUNGU WASWA 58
  • LABORATORY DIAGNOSIS OF FOOD POISONING • Specimen: Left over food, vomits, stool • Culture the specimen for microbial isolation. • Serological technique for toxin isolation. • Treatment: Depends on the causative agent. WALTER WAKHUNGU WASWA 59
  • MYCOTOXINS • Ergotism – toxic condition caused by growth of a fungus in grains • Aflatoxins – carcinogens produced in fungus-infected grains and nut products • Fumonisins – Carcinogens produced in fungus-infected corn • ACRATOXINS WALTER WAKHUNGU WASWA 60
  • Controlling Food Spoilage 1 2 3 4 5 6 7 WALTER WAKHUNGU WASWA 62
  • Canned food spoilage organisms may be characterized as follows: • Mesophilic organisms -Putrefactive anaerobes -Butyric anaerobes -Aciduric flat sours -Lactobacilli -Yeasts -Molds • Thermophilic organisms -Thermophilic anaerobes producing sulfide -Flat-four spores -Thermophilic anaerobes not producing WALTER WAKHUNGU WASWA 63
  • Radiation 1.ultraviolet (UV) radiation – used for surfaces of food-handling equipment – does not penetrate foods 2.Gamma radiation – use of ionizing radiation (gamma radiation) to extend shelf life or sterilize meat, seafoods, fruits, and vegetables 3.Beta rays-may be defined as a stream of electrons emitted from radioactive substances. 4.Microwaves WALTER WAKHUNGU WASWA 65
  • NATURE RADIATION RESISTANCE OF MICROORGANISMS • The most sensitive bacteria to ionizing radiation are gram-negative rods such as the pseudomonas • the coccobacillary-shaped gramnegative cells of moraxellae and acinetobacters are among the most resistant of gram negatives. • Gram-positive cocci are the most resistant of nonsporing bacteria, including micrococci,staphylococci, and enterococci. WALTER WAKHUNGU WASWA 66
  • IRRADIATION • Types of Organisms • Gram-positive bacteria are more resistant to irradiation than gram negatives. • Spore formers are more resistant than nonspore formers. WALTER WAKHUNGU WASWA 67
  • Characteristics of radiation resistant microorganisms 1).can survive 15 kGy eg D. radiophilus 2).contain red water-insoluble pigments (carotenoid) plasma membrane is red, 3).contain L-ornithine as the basic amino acid in their murein 4).Posses an outer membrane 5).High content of fatty acid in their envelope 6).Abudant DNA-Actively dividing cells may contain 4 to 10 copies WALTER WAKHUNGU WASWA 68
  • EFFECTIVENESS OF RADIATION TECHNOLOGY IS DETERMINED BY: 1.Numbers of Organisms The larger the number of cells, the less effective is a given dose. 2.Composition of Suspending Menstrum (Food) • Microorganisms in general are more sensitive to radiation when suspended in buffer solutions 3.Presence or Absence of Oxygen • The radiation resistance of microorganisms is • greater in the absence of oxygen than in its presence WALTER WAKHUNGU WASWA 69
  • 4.Physical State of Food • The radiation resistance of dried cells is, in • general, considerably higher than that for moist • cells. 5.Age of Organisms • Bacteria tend to be most resistant to radiation in the lag phase just prior to active cell division. WALTER WAKHUNGU WASWA 70
  • How do we effectively Detect FoodBorne Pathogens? First the method must be rapid and sensitive • methods include: – culture techniques – may be too slow – immunological techniques - very sensitive – molecular techniques • probes used to detect specific DNA or RNA • sensitive and specific WALTER WAKHUNGU WASWA 71
  • Surveillance for food-borne disease • PulseNet – established by Centers for Disease Control – uses pulsed-field gel electrophoresis under carefully controlled and duplicated conditions to determine distinctive DNA pattern of each bacterial pathogen – enables public health officials to link pathogens associated with disease outbreaks in different parts of the world to a specific food source WALTER WAKHUNGU WASWA 72
  • Surveillance… • FoodNet – active surveillance network used to follow nine major food-borne diseases – enables public health officials to rapidly trace the course and cause of infection in days rather than weeks WALTER WAKHUNGU WASWA 73
  • Helpful Suggestions •Refrigerate quickly •Wash hands •Clean cutting boards •Leftovers •Avoid home-canned foods WALTER WAKHUNGU WASWA 74
  • Microbiology of Fermented Foods • Major fermentations used are lactic, propionic, and ethanolic fermentations • Fermentation=Any partial breakdown of carbohydrates taking place in the absence of oxygen. WALTER WAKHUNGU WASWA 75
  • Meat and Fish Fermented Products • • • • • • Sausages Hams Bologna Salami Izushi – Fish, Rice And Vegetables Katsuobushi – Tuna WALTER WAKHUNGU WASWA 78
  • Wine White vs. Red: juice or juice and skin Yeasts: Ferment when no oxygen around. Saccharomyces species Dry Sweet Sparkling Fortified WALTER WAKHUNGU WASWA 79
  • Production of Breads • involves growth of Saccharomyces cerevisiae (baker’s yeast) under aerobic conditions – maximizes CO2 production, which leavens bread • other microbes used to make special breads (e.g., sourdough bread) • can be spoiled by Bacillus species that produce ropiness WALTER WAKHUNGU WASWA 80
  • Other Fermented Foods • silages – fermented grass, corn, and other fresh animal feeds WALTER WAKHUNGU WASWA 81
  • Microorganisms as Foods and Food Amendments • variety of bacteria, yeasts, and other fungi are used as animal and human food sources • probiotics – microbial dietary adjuvants – microbes added to diet in order to provide health benefits beyond basic nutritive value WALTER WAKHUNGU WASWA 82
  • PSYCHROPHILICMICROORGANISMS • This term is applied to organisms that grow over the range of subzero to 20C.Are those organisms capable of growing relatively rapidly at commercial refrigeration temperatures with out reference to optimum temperature for growth. Species of Pseudomans, Achromobacter, flavobacterium and Alcahigenes are examples of Psychrophilic bacteria. • Large no=change in flavors as well as defects in foods. WALTER WAKHUNGU WASWA 83
  • Thermophilic microorganism  Thermophilic microorganisms are those organisms which will survive so significant measure of heat treatment . The thermophilic organisms not only survive the heat treatment but also grow at the elevated temperature . Thermoduric bacteria are important with regard to milk and milk products as they may survive pastourisation temperature. Those of greatest importance in foods belong to the genera Bacillus, Clostridium, and Thermoanaerobacterium. WALTER WAKHUNGU WASWA 84
  • XTERISTICS OF THERMOPHYLIC MICROORGANISMS • On the basis of growth temperatures, thermophiles may be characterized as organisms with a minimum of around 45C, an optimum between 50C and 60C, and a maximum of 70C or above. WALTER WAKHUNGU WASWA 85
  • EXAMPLES • Genera Lactobacillus, Bacillus and Clostridium are recognized as containing some species which will qualify as thermoduric. WALTER WAKHUNGU WASWA 86
  • STAPHYLOCOCCUS • • • • The three main species of clinical importance Staphylococcus aureus Staphylococcus epidermidis Staphylococcus saprophyticus WALTER WAKHUNGU WASWA 87
  • cont • Can readily grow in ordinary media under aerobic and microaerophilicconditions • grow most rapidly at 37 0c but form pigment best at room • temperature of 20-25 oc WALTER WAKHUNGU WASWA 88
  • cont • Some of them are normal flora of the skin and mucus membrane of human, otrhhers cause suppuration abscess • Formation and fatal septicemia • Produce catalase, which differentiate them from the streptococci. • Converts H202 into H20 and 02 WALTER WAKHUNGU WASWA 89
  • toxins  Exotoxins(α, β, γ, δ)  . Enterotoxin-Produced by S.aureus when grown in  carbohydrate and protein foods.  Multiple (A-E, G-I, K-M) soluble heat-stable, gut enzyme resistant toxins which act on neural receptors in the gut to stimulate vomiting center in the central nervous system.  It is superantigen causing staphylococcal food poisoning  . WALTER WAKHUNGU WASWA 90
  • cont • Toxic shock syndrome toxin- Superantigen desquamative toxin Produced by S.aureus and Causes fever, shock,multiple-organ failure and skin rash. • . Exfoliative toxin-Epidermolytic superantigen produced by WALTER WAKHUNGU WASWA 91
  • Incidence in Delicatessen and related foods • Delicatessen foods, such as salads and sandwiches, are sometimes involved in foodpoisoning outbreaks. These foods are often prepared by hand, and this direct contact may lead to an increased incidence of food poisoning agents such as Staphylococcus. Once organisms such as these enter meat salads or sandwiches, they may grow well because of the reduction in numbers of the normal food biota by the prior cooking of salad ingredients. WALTER WAKHUNGU WASWA 92
  • incidences • Most microorgansm are enteric bacteria and some environmental fungi • Staphylococcus • S.aureus • C.perfringens • E.coli • Yeast and moulds • Corliforms WALTER WAKHUNGU WASWA 93
  • Determining microorganisms and their products in food • The examination of foods for the presence, types, and numbers of microorganisms and/or their products is basic to food microbiology. • Culture • Microscopic examination • Sampling WALTER WAKHUNGU WASWA 94
  • Direct microscopy In its simplest form, the DMC consists of making smears of food specimens or cultures onto a microscope slide, staining with an appropriate dye, and viewing and counting cells with the aid of a microscope (oil immersion objective). WALTER WAKHUNGU WASWA 95
  • sterilization : Destruction of all forms of microbial life including spores. WALTER WAKHUNGU WASWA 96
  • How would you determine efficiency of a sterilizer 1. Recording of temperature and time of each sterilizing cycle. 2. Heat-sensitive autoclave tape fixed to the outside of each pack. .. Color change of autoclave tape from blue to brown-black indicates completesterilization. 4. Biological indicator : Use of paper strips impregnated with spores of Bacillus stereothermophilus WALTER WAKHUNGU WASWA 97
  • Quality of water  quality of water is odorless, colorless, tasteless and free from fecal pollution and harmful chemicals. Human illness is caused by water supplies becoming contaminated from feces being passed or washed into rivers, streams, or being allowed to seep into wells. Feces contain microorganisms like Escherichia coli, Streptococcus faecalis and Clostridium perfringenes, which contaminate safe water. WALTER WAKHUNGU WASWA 98
  • lab Determining whether a water supply is fecally polluted is to test for the presence of normal fecal organism. Testing for normal fecal organisms as indicators of fecal pollution is a reliable way of determining whether water is bacteriologically safe to drink. WALTER WAKHUNGU WASWA 99
  • coliforms Organisms used as indicators of fecal pollution are the coliform group particularly E. coli. WALTER WAKHUNGU WASWA 100
  • Food contamination Food may acquire their micro-organism from various sources and the following are the important sources. WALTER WAKHUNGU WASWA 101
  • 1. Animals - Animals could be a source of contamination of food. - The surface of animals, the respiratory tract, the gastrointestinal tract, hides, Loofs and waste products of animals are important sources of contamination. WALTER WAKHUNGU WASWA 102
  • 2. Plants - Food may get their microbial contamination from green plants. - The natural flora of growing plants includes pseudomonas, alcaligenes,bacissus, Micrococcus, coliform etc. WALTER WAKHUNGU WASWA 103
  • 3. Sewage - Gastrointestinal pathogens, coliforms, Enterococci of untreated domestic sewage could be source of contamination of raw plant foods. - Sewage can also contaminate natural waters and contribute micro-organisms to shellfish, fish and other sea foods. WALTER WAKHUNGU WASWA 104
  • 4. Soil - Soil is a very rich environment in microbes and is a major source of contamination of food. - Bacillus, clostridium, enterobacter, Escherichia, Micrococcus, Alkaligens, Flavobacterium, Pseudomonas, proteus, Aerobacter, molds and yeast are kinds of organisms that contaminate food from soil. 5. Air and water:- are also important source of food contamination.- WALTER WAKHUNGU WASWA 105
  • MICROORGANISM IMPORTANT IN FOOD 1.Indicator microoganisms Indicator organisms are bacterial groups (or species) whose presence in foods, above a certain numerical limits, is considered to indicate exposure of food to conditions that might introduce hazardous organisms and/or allow proliferation of pathogenic or toxinogenic species. WALTER WAKHUNGU WASWA 106
  • Indicator organisms Include coliforms and faecal streptococci. Coliform group is defined to include all aerobic and faculitative anaerobic, gram negative, non-spor forming, rod shaped species which ferment lactose with the production of acid and gas within 48 hours at 35C • Coliform are either part of the normal flora of intestinal tract of man and animals or found in environments such as soil and plants. WALTER WAKHUNGU WASWA 107
  • Coliform that are commonly found in the intestinal tracts of man and animals (faeces) are called faecal coliform and those coliforms that are normal inhabitants of soil and plants are called non faecal coliform. WALTER WAKHUNGU WASWA 108
  • 2.INDEX MICROORGANISMS =is one whose presence implies the possible occurance of a similar but pathogenic organism.E. coliis used an index organism and its presence indicates possible presence of pathogenic enteriobacteriacea eg.salmonellae species. WALTER WAKHUNGU WASWA 109
  • 3.FOOD POISONING MICROORGANISMS • those which cause the disease by infection • those which produce toxin in food WALTER WAKHUNGU WASWA 110
  • Those which cause infection must grow in food in large numbers and cause infection when consumed together with food. The most most common microorganisms includes salmonella tyhimurrium, entropathogenicE.coli,Vibrio parahaemolyticus etc. WALTER WAKHUNGU WASWA 111
  • Those which cause intoxication must grow in food large numbers and produce enough toxin and when consumed together with food cause intoxication.The most common microorganism in this group are clostridium botulinium,staphylococcus and toxigenic fungi eg. Aspergillus flavus. WALTER WAKHUNGU WASWA 112
  • 5.INFECTIOUS MICROORGANISMS Organisms whose presence in small numbers in food and when consumed can cause infection. In this case the food acts as avector but not necessarly as a growth medium.organisms in this group are, Vibrio choleraeO1, salmonella typhi, shigella sonnei,Bacillus anthracis, HepatitisB virus etc. WALTER WAKHUNGU WASWA 113
  • 6.Spoilage microorganisms The spoilage microorganisms include bacteria, yeasts and moulds that cause undesirable changes of the appearance, odour, texture or taste of the food. They are commonly grouped according to their type of activity or according to theiri growth reguirements. a) Psychrophilic microorganisms b) Lipolytic Microorganisms c) Proteolytic microorganisms d) Halophilic microorganisms WALTER WAKHUNGU WASWA e) Halotolerant organisms 114
  • f)Acid producing microorganisms g)Yeasts and moulds h)Mesophillic spore forming aerobes i)Thermophillic anaerobes WALTER WAKHUNGU WASWA 115
  • Microbiological examination of food • Sampling should be carried • Sampling out aseptically • It is important to not • Samples should be that samples of foods protected against collected for extraneous contamination microbiological analysis • Moreover, samples must should reflect the be held under conditions microbiological thatpermit neither die off condition at the time of nor multiplication of the collection. This implies original that • microflora present in the WALTER WAKHUNGU WASWA 116 food.
  • Terms used • A LOT:Is a quantity of food produced and handled under uniform • condition. This means that food produced within a batch or • in a continuous process a food produced within a limited • period of time • FILED SAMPLE:The amount of material actually used in the analysis of food for microorganisms. The sample unit is recommended to be 25 g for all types of food WALTER WAKHUNGU WASWA 117
  • Microbiological criteria • is a microbiological value (eg. Number of microorganism per g of food) or a range established by use of defined procedures and includes the following information. • ENDELEA WALTER WAKHUNGU WASWA 118
  • STAPHYLOCOCCUS • Characteristics: • Gram positive non spore-forming non-motile, spherical cells, usually arranged in grape-like clusters • The three main species of clinical importance • Staphylococcus aureus • Staphylococcus epidermidis • Staphylococcus saprophyticus WALTER WAKHUNGU WASWA 119
  • HABITAT • Some of them are normal flora of the skin and mucus membrane of human, others cause suppuration abscess formation and fatal septicemia • relatively resistant to drying , heat, and 9% NacI, but readily inhibited by 3 % hexachlorophene WALTER WAKHUNGU WASWA 120
  • TOXINS PRODUCED BY STAPHYLOCOCCUS . Exotoxins(α, β, γ, δ) . Enterotoxin-Produced by S.aureus when grown in carbohydrate and protein foods. Multiple (A-E, G-I, K-M) soluble heat-stable, gut enzyme resistant toxins which act on neural receptors in the gut to stimulate vomiting center in the central nervous system. It is superantigen causing staphylococcal food poisoning . Toxic shock syndrome toxin- Superantigen desquamative toxin Produced by S.aureus and Causes fever, shock, multiple-organ failure and skin rash. . Exfoliative toxin-Epidermolytic superantigen produced by S.aureus and uses generalized desquamation of the skin. WALTER WAKHUNGU WASWA 121
  • . Food poisoning: Caused by enterotoxin produced by S.aureus PREVENTION AND CONTROL? ?????????????????????????????????????????????? WALTER WAKHUNGU WASWA 122
  • STREPTOCOCCUS • They are non-motile, non- sporulating, grampositive facultative anaerobes • Spherical or oval cells characteristically forming pairs or chains during growth. • They are widely distributed in nature and are found. • in upper respiratory tract, gastrointestinal tract and genitourinary tract as normal microbial flora. WALTER WAKHUNGU WASWA 123
  • BACILLUS • Characteristics: • • Aerobic, non-motile,spore-forming, grampositive chain • forming rods. • • Bacillus species are ubiquitous saprophytes • Important human pathogen • B. anthracis • B. cereus WALTER WAKHUNGU WASWA 124
  • B.CEREUS • General characteristics: • Exhibit motility by swarming in semisolid media • Produce β lactamase, so not sensitive to penicillin WALTER WAKHUNGU WASWA 125
  • CLINICAL FEATURES • 1. Food poisoning Pathogenicity determinant: Exotoxin a.Emetic type food poisoning IP is 1-5 hrs after ingestion of preformed toxin contaminating rice and pasta dishes Characterized by nausea, vomiting, abdominal cramps, and self-limited with in 24 hrs b. Diarrheal type food poisoning IP is 1-24 hrs after ingestion of contaminated meat dishes with sporulating or preformed toxin Characterized by profuse diarrheaand abdominal cramps. Fever and vomiting is uncommon WALTER WAKHUNGU WASWA 126
  • CLOSTRIDIUM PERFRINGEN • Characteristics: • Clostridia are anaerobic, spore-forming motile, gram-positive rods. • Most species are soil saprophytes but a few are pathogens to human. • They inhabit human and animal intestine, soil, water, decaying animal and plant matter WALTER WAKHUNGU WASWA 128
  • PATHOGENICITY • 1. Enzymes: Digest collagen of subcutaneous tissue andmuscle.. Collagenase. Proteinase. Hyaluronidase. Dnase • 2. Toxins. PhospholipaseC (α toxin) • It has lethal, necrotizing and hemolytic effect on tissue. It causes cell lysis due to lecithinase action on the lecithin which is found in mammalian cell membrane. • . Theta toxin It has hemolytic and necrotic effect on tissue. WALTER WAKHUNGU WASWA 129
  • Clinical manifestation: • 1. Clostridial myonecrosis: Gas gangrene • . IP(Incubation period) =1-3 days Colonization of devitalized tramatized wound by C.perfringens spores, and organism germiation and release of toxins Presentation: Muscle and subcutaneous tissue necrosiss andcrepitationFoul smelling wound discharge • Fever, toxaemia, hemolytic anemia, Shock WALTER WAKHUNGU WASWA 130
  • CLOSTRIDIUM BOTULINUM • • Spores of C. botulinum are widely distributed in soil, they often contaminate vegetables, fruits and other materials. • Produce a neurotoxin which is the most active • known poison, and considered to be the major agent of bioterrorism and biologic warfare WALTER WAKHUNGU WASWA 131
  • PATHOGENESIS • 1. Food botulism . INCUBATION PERIOD = 18-24 hrs . Route of entry is under cooked consumption of C.botulinum toxin contaminated spiced, smoked, vaccumpacked or canned food .The toxin is absorbed from the gut and acts by blocking the release of acetylcholine at synapses and neuromuscular junction and manifests with flaccid paralysis and visual disturbance, inability to swallow, and speech difficulty.Death is secondary to respiratory failure or cardiac arrest WALTER WAKHUNGU WASWA 132
  • CONT… • 2. Infantile botulism C.botulinum implicated and affects infants when mixed feeding starts (after fourth month of life). • Ingestion and colonisation of the gut with C.botulinum, and production of toxin and adsorption of toxin leads to poor feeding, paralysis (floppy baby), and cranial nerve palsy. • Diagnosed by demonstration of the organism or toxin from the stool. WALTER WAKHUNGU WASWA 133
  • BRUCELLOSIS • Brucellosis/ Undulant fever • 2 stages of illness 1. Acute stage: Fever, malaise, sweating, hepatosplenomegally, lymphadenopathy • Associated with 80% spontaneous recovery • Prevention and control: Pasteurization of milk and milk products Slaughter of all infected animals in dairy herds Vaccination of cattle. WALTER WAKHUNGU WASWA 134
  • ESCHERICHIA COLI • Characteristics: • . Normal flora in human and animal gastrointestinal tract. • . Found in soil, water and vegetation. • . Most are motile; some are capsulated. • . E.coli-associated diarrheal disease WALTER WAKHUNGU WASWA 135
  • DIARRHOEA • 1. Enteropathogenic E.coli(EPEC) . causes outbreaks ofself-limiting infantile diarrhea . they also cause severe diarrhea in adults • 2. Enteroinvasive E.coli(EIEC) invade the mucosa of the ileum and colon, and causes shigellosis-like dysentery WALTER WAKHUNGU WASWA 136
  • 3. Enterotoxigenic E.coli(ETEC) adherence to epithelial cells of small intestine followed by release of enterotoxin which causes toxin-mediated watery diarrhea in infants and young adults. . It is an important cause of traveller’s diarrhea 4. Entero haemorrhagic E.coli( EHEC) causes haemorrhagic colitis (severe form of diarrhea) 5. Enteroaggressive E.coli( EAEC) .Adhere to human intestinal mucosal cells and produce ST-like toxin and hemolysin, and causes acute and chronic diarrhea WALTER WAKHUNGU WASWA 137
  • SALMONELLA • Species of medical importance are:S. typhi S. paratyphi S. enteritidis WALTER WAKHUNGU WASWA 138
  • CLINICAL PATHOGENESIS • 1. Enteric fever:It is caused by S.typhi and S.paratyphi, and transmitted by fecal-oral route via contaminated food and drinks Incubation period: 10-14 days Predisposing factors: .Reduced gastric acidity .Disrupted intestinal microbial flora .Compromised local intestinal immmunity WALTER WAKHUNGU WASWA 139
  • CONT.. • Both manifest with persistent fever, headache, malaise, chills, enlargement of liver and spleen, and skin rashes. • Paratyphoid fever is milder than typhoid fever Complications: Intestinal perforation Lower gastrointestinal bleeding Dissenmination to different body organs WALTER WAKHUNGU WASWA 140
  • 2. Gastroenteritis • • • • • • • • It is caused by S. enteritidis S. typhimurium IP= 8-48 hrs It manifests with initial watery diarrhea, and later bloody mucoid diarrhea associated with crampy abdominal pain and tenesmus. Bacteremia is rare (2-3 % of cases) It usually resolves in 2-3 days WALTER WAKHUNGU WASWA 141
  • SHIGELLOSIS • • • • • S. dysenteriae S. flexneri S. boydii S. sonnei In developing countries, shigellosis (bacillary dysentery) is caused by S. flexneri and S. dysenteriae. WALTER WAKHUNGU WASWA 142
  • • Pathogenesis and Clinical features: • Route of infection is fecal-oral route Inoculum dose: 103 organisms Pathogenicity determinant:Toxins: • Endotoxin: irritate the bowel wall • Exotoxin: Enterotoxin and neurotoxin • S.dysenritiae type 1(shiga bacillus) produce heat labile exotoxinmediated diarrhea • IP: 1-2 days WALTER WAKHUNGU WASWA 143
  • • It causes shigellosis (bacillary dysentery) characterized by sudden • onset of bloody mucoid diarrhea, abdominal cramp, tenesmus, fever, • generalized muscle ache and weakness. • Complication: Dehydration • Electrolyte and acid-base disturbance • High prevalence: Poor sanitation • Poor personal hygiene • Polluted water supply • Young children are frequently affected. WALTER WAKHUNGU WASWA 144
  • YERSINIA • Animals are natural hosts of yersinia, and humans are accidental hosts of yersinia infection • Important human pathogens • Y. pestis • Y. pseudotuberculosis • Y. enterocolitica WALTER WAKHUNGU WASWA 145
  • • Yersinia pestis • . Plague bacillus with gram negative, nonmotile, facutatively • anaerobe possessing bipolar granules WALTER WAKHUNGU WASWA 146
  • • Pathogenesis and clinical features: • Rat flea (Xenopsylla cheopis) gets infected by biting an infected rodent → infected rat flea bites human (accidental host) → organism migrate to regional lymphnodes from the site of bite (bubonic plaque) and gets into the blood via lymphatics (septicemic plaque), or Primary pneumonic plaque results from inhalation of infective droplets, usually from an infected coughing person • IP=2-6 days • Human Plaque: 3 types WALTER WAKHUNGU WASWA 147
  • • • • • • • • 1. Bubonic plague: Fever, vomiting, painful lymphadenitis(buboes) in the groin or axillae 2. Pneumonic plague: Ip is 1-3 days Profuse mucoid or bloody expectoration with signs of pneumonia 3. Septicemic plague Fever, vomiting, diarrhea, hypotension, altered • mentation, renal and heart failure, intra vascular • coagulopathy WALTER WAKHUNGU WASWA 148
  • • HUMAN INFECTION • Human infection results from ingestion of food and drinks contaminated by animal feces • Antigenic structure • . Inv (invasion) locus • . AIL (attachement invasion locus) • Pathogenesis and clinical feature: • Route of transmission: Contaminated food and drinks • Inoculum dose: 108-109 org • IP=5-10 days WALTER WAKHUNGU WASWA 149
  • Cont… • . Fever, abdominal pain, toxin and invasionmediated diarrhea • Usually self-limited disease • Post-diarrheal diseases • Arthritis • skin rash/nodules • Complication: Sepsis/ Meningiti WALTER WAKHUNGU WASWA 150
  • VIBRIO . Actively motile, gram-negative curved rods. . Species of medical importance: Vibrio cholerae • Characteristics: 1.Found in fresh water, shellfish and other sea food..Man is the major reservoir of V. cholerae-01, which causes epidemic cholera. 2. Readily killed by heat and drying; dies in polluted water but may survive in clean stagnant water, esp. if alkaline, or sea water for 1-2 weeks. WALTER WAKHUNGU WASWA 151
  • • CLINICAL FEATURES: • Route of infection is fecal-oral route. • After ingestion of the V.cholerae-01, the bacteria adheres to the intestinal wall with out invasion then produces an exotoxin causingexcessive fluid secretion and diminished fluid absorption resulting in diarrhea (rice water stool) which is characterized by passage of voluminous watery diarrhea containing vibrios, epithelial cells and mucus; and result in severe dehydration. WALTER WAKHUNGU WASWA 152
  • CAMPYLOBACTER • Characteristics: • Small, delicate, spirally curved gram-negative bacteria. • Motile bacteria with single polar flagellum. • . Stricly microaerophilic bactria requiring 510% o2 and 10% co2 enriched environment. WALTER WAKHUNGU WASWA 153
  • Clinical features: • Inoculum dose: 104 organisms • Source of infection is contaminated food, drinks,and unpasteurized milk • The organism multiply in small intestine, invade the epithellium and produce inflammation Campylobacter enteritis manifests with fever, headache, malaise, crampy abdominal pain and bloody mucoid diarrhea, and usually selflimited enteritis in a week period • Laboratory diagnosis: • Specimen: Stool WALTER WAKHUNGU WASWA 154
  • LISTERIOSIS • General characteristics: • . Widely present in plants, soil and surface water • . Zoonotic pathogen of domestic animals • . Non-sporulating, facultative anaerobe, intracellular. Gram positive rods WALTER WAKHUNGU WASWA 155
  • Pathogenesis and clinical features: • Transmitted to humans through ingestion of poorly coooked • meat and unpasteurized milk and milk products • 1. Perinatal human listeriosis: Granulomatous • infantisepticum • . Early onset syndrome: Intrauterine sepsis • . Late onset syndrome: Neonatal meningitis WALTER WAKHUNGU WASWA 156
  • Cont…… • In Adults • . Meningoencephalitis • . Bacteremia Prevention and control: • Proper cooking of animal souce foods • Pasteurization of milk and milk products/ WALTER WAKHUNGU WASWA 157
  • parasites • The animal parasites that can be contracted by eating certain foods belong to three distinct groups: protozoa, flatworms, and roundworms. • Animal parasites do not proliferate in foods. WALTER WAKHUNGU WASWA 158
  • PROTOZOA • Giardiasis Giardia lamblia is a flagellate protozoan that exists in environmental waters. • The protozoal cells (trophozoites) produce cysts, which are the primary forms in water and foods. • Upon ingestion, Giardia cysts excyst in the • gastrointestinal tract with the aid of stomach acidity and proteases and give rise to clinical giardiasis in some individuals. WALTER WAKHUNGU WASWA 159
  • • Excystation of the trophozoites occurs somewhere in the upper small intestine, and this step is regarded as being equivalent to a virulence factor. • The trophozoites are not actively phagocytic, and they obtain their nutrients by absorption. Occasionally, bile ducts are invaded, leading to cholecystitis. • ENVIRONMENTAL DISTRIBUTION • Water=waterborne WALTER WAKHUNGU WASWA 160
  • giardiasis • The incubation period for clinical giardiasis is 7-13 days, and cysts appear in stools after 3-4 weeks. Asymptomatic cyst passage is the most benign manifestation of G. lamblia infectionin humans, but when clinical giardiasis occurs, symptoms may last from several months to a year or more. Up to 9.0 x 108 cysts are shed each day by patients, and they may survive as long as 3 months in sewage sludge. WALTER WAKHUNGU WASWA 161
  • Clinical symptoms • • • • • • • Abdominal cramps Abdominal distention Weigh loss Diarrhoea Fatigue Vomiting Nausea WALTER WAKHUNGU WASWA 162
  • • Giardiasis is a highly contagious disease. It has been documented in daycare centers where unsanitary conditions prevailed. The human infection rate ranges from 2.4% to 67.5%.18 The minimum infectious dose of G. lamblia cysts for humans is 10 or less. WALTER WAKHUNGU WASWA 163
  • Giardiasis is diagnosed by the demonstration • of trophozoites in stool specimen by microscopic examinations using either wet mounts or stained specimens. G. lamblia can be grown in axenic culture, but this does not lend itself to rapid diagnosis. • Effective enzyme-linked immunosorbent assay (ELISA) tests have been developed. WALTER WAKHUNGU WASWA 164
  • The drug of choice for the treatment of giardiasis • is quinacrine, an acridine derivative. Also effective are metronidazole and tinidazole. WALTER WAKHUNGU WASWA 165
  • Incidence in Foods and Foodborne Cases • Giardia has been shown to occur in some vegetables, and it may be presumed that the organism occurs on foods that are washed with contaminated water or contaminated by unsanitary asymptomatic carriers. WALTER WAKHUNGU WASWA 166
  • Amebiasis • Amebiasis (amoebic dysentery), caused by Entamoeba histolytica, is often transmitted by the fecal-oral route, although transmission is known to occur by water, food handlers, and Foods. • In warm stools from a case of active dysentery, E. histolytica is actively motile and usually contains red blood cells that the protozoan ingests by pseudopodia. WALTER WAKHUNGU WASWA 167
  • • Although generally outnumbered in stools by Entamoeba coli, the latter never ingests red blood cells. • Although the trophozoites do not persist under environmental conditions, the encysted forms can survive as long as 3 months in sewage sludge. • The possible transmission of cysts to foods becomes a real possibility when poor personal restroom hygiene is practiced. WALTER WAKHUNGU WASWA 168
  • • • • • • In its trophozoite stage, the organism induces infection in the form of abscesses in intestinal mucosal cells and ulcers in the colon. It reproduces by binary fission in the large intestine. It encysts in the ileum, • and cysts may occur free in the lumen. The • organism produces an enterotoxic WALTER WAKHUNGU WASWA 169
  • • Syndrome, Diagnosis, and Treatment The incubation period for amebiasis is 2-4 weeks, and symptoms may persist for several • months. Its onset is often insidious, with loose • stools and generally no fever. Mucus and blood • are characteristic of stools from patients. Later • symptoms consist of pronounced abdominal • pain, fever, severe diarrhea, vomiting, and lumbago, • and somewhat resemble those of shigellosis. WALTER WAKHUNGU WASWA 170
  • • Amebiasis is diagnosed by demonstrating trophozoites • and cysts in stools or mucosal • scrapings. Immunological methods such as indirect • hemagglutination, indirect immunofluorescence, • latex agglutination, and ELISA are • useful. WALTER WAKHUNGU WASWA 171
  • • This syndrome can be treated with the amebicidal drugs metronidazole and chloroquine. WALTER WAKHUNGU WASWA 172
  • • Toxoplasmosis • This disease is caused by Toxoplasma gondii, • a coccidian protozoan that is an obligate intracellular • parasite. WALTER WAKHUNGU WASWA 173
  • • Domestic and wild cats are the only definitive hosts for the intestinal or sexual phase of this organism, making them the primary sources of human toxoplasmosis. Normally, the disease is transmitted from cat to cat, but virtually all vertebrate animals are susceptible to the oocysts shed by cats. As few as 100 oocysts can produce clinical toxoplasmosis in humans, and the oocysts can survive over a year in warm, moist environments. WALTER WAKHUNGU WASWA 174
  • • Symptoms, Diagnosis, and Treatment • In most individuals, toxoplasmosis is symptomless,but when symptoms occur, they consist of fever with rash, headache, muscle aches and • pain, and swelling of the lymph nodes. The • muscle pain, which is rather severe, may last up • to a month or more. WALTER WAKHUNGU WASWA 175
  • cycle • The disease is initiated upon the ingestion of • oocysts (if from cat feces), which pass to the intestine • where digestive enzymes effect the release • of the eight motile sporozoites. WALTER WAKHUNGU WASWA 176
  • • Fresh meats may contain toxoplasma oocysts. • Undercooked meat was suspected to be the source of human toxoplasmosis. WALTER WAKHUNGU WASWA 177
  • • Control • Toxoplasmosis in humans can be prevented by avoiding environmental contamination with cat feces and by avoiding the consumption of meat and meat products that contain viable tissue cysts. The cysts of 7. gondii can be destroyed by heating meats above 600C or by irradiating at a level of 30 krad (0.3 kGy) or higher. The organism may be destroyed by freezing. WALTER WAKHUNGU WASWA 178
  • • Sarcocystosis • Of the more than 13 known species of the genus Sarcocystis, two are known to cause an extraintestinal disease in humans. One of these is obtained from cattle (S. hominis) and the other from pigs (S. suihominis). Humans are the definitive hosts for both species; the intermediate host for S. hominis is bovines, and pigs for S. suihominis.When humans ingest a sarcocyst, bradyzoites are released and penetrate the lamina propria of the small intestine, where sexual reproduction occurs that leads to sporocysts. WALTER WAKHUNGU WASWA 179
  • • Since most of the above cases have been traced to meats, the consumption of raw or undercooked meats carries the risk of this infection. WALTER WAKHUNGU WASWA 180
  • Cryptosporidiosis • The protozoan Cryptosporidiunparvum was first described in asymptomatic mice, and for decades now it has been known to be a pathogen of at least 40 mammals and varying numbers of reptiles and birds. Although the first documented human case was not recorded until 1976, this disease has a worldwide prevalence of 1-4% among patients with diarrhea,96 and it appears to be increasing. WALTER WAKHUNGU WASWA 181
  • • The prevalence of C. parvum in diarrheal stools is similar to that of Giardia lamblia. In humans, the disease is self-limiting in immunocompetent individuals, but it is a serious infection in the immunocompromised, such as AIDS patients. The protozoan is known to be present in at least some bodies of water and thus exists the potential for food transmission.The fecal-oral route of transmission is the most important, but indirect transmission by food and milk is known to occur. WALTER WAKHUNGU WASWA 182
  • • C. parvum carries out its life cycle in one host. Following ingestion of the thick-walled oocysts, they excyst in the small intestine and free sporozoites that penetrate the microvillous region of host enterocytes, where sexual reproduction leads to the development of zygotes. They invade host cells by disrupting their own membrane as well as that of the host. WALTER WAKHUNGU WASWA 183
  • • Symptoms, Diagnosis, and Treatment • The clinical course of cryptosporidiosis in • humans depends on the immune state, with the • most severe cases occurring in the immunocompromised. • In immunocompetent individuals, • the organism primarily parasitizes the intestinal epithelium and causes diarrhea. WALTER WAKHUNGU WASWA 184
  • • FLATWORMS • AU flatworms belong to the animal phylum • Platyhelminthes, WALTER WAKHUNGU WASWA 185
  • • Fascioliasis • This syndrome (also known as parasitic biliary • cirrhosis and liver rot) is caused by the digenetic • txQmdXo&t Fasciola hepatica. The disease • among humans is cosmopolitan in distribution, • and the organism exists where sheep and cattle WALTER WAKHUNGU WASWA 186
  • • in humans results • from eating raw Fflsczo/fl-ladedbovine liver • where young flukes become attached to the buccal • or pharyngeal membranes, resulting in pain, • hoarseness, and coughing.18 WALTER WAKHUNGU WASWA 187
  • • Symptoms, Diagnosis, and Treatment • Symptoms develop in humans about 30 days • after the infection; they consist of fever, general • malaise, fatigue, loss of appetite and weight, and • pain in the liver region of the body. WALTER WAKHUNGU WASWA 188
  • • Fasciolopsiasis • Fasciolopsiasis is caused by Fasciolopsis buski, and the habitat of this organism is similar to that of E hepatica. • Humans serve as definitive host, • Snails serve as first intermediate hosts, and water plants (watercress nuts) as second intermediate hosts. WALTER WAKHUNGU WASWA 189
  • • no symptoms • occurring when only a few parasites exist In the body. When symptoms occur, they develop within 1-2 months after the initial infection and consist of violent diarrhea, abdominal pain, loss of weight, and generalized weakness. WALTER WAKHUNGU WASWA 190
  • • Paragonimiasis • This parasitic disease (also known as parasitic • hemoptysis) is caused by Paragonimus spp., especially P. westermani. WALTER WAKHUNGU WASWA 191
  • Diphyllobothriasis • Contracted from the consumption of raw or undercooked fish, • Causative organism, Diphyllobothrium latum, fish tapeworm. • Definitive hosts are humans andother fisheating mammals; • Intermediate hosts are various freshwater fish and salmon, where plerocercoid (or metacestode) larvae are formed. WALTER WAKHUNGU WASWA 192
  • • Symptoms, Diagnosis, and Treatment • Although most cases of diphyllobothriasis are • asymptomatic, victims may complain of epigastric • pain, abdominal cramps, vomiting, loss of • appetite, dizziness, and weight loss. Intestinal • obstruction is not unknown. WALTER WAKHUNGU WASWA 193
  • • Prevention • Diphyllobothriasis can be prevented in humans • by avoiding the consumption of raw or • undercooked fish. WALTER WAKHUNGU WASWA 194
  • • Cysticercosis/Taeniasis • This syndrome in humans is caused by two • species offlatworms: Taeniasaginata (also Taeniarhynchus • saginatus; beef tape) and Taenia • solium (pork tape). WALTER WAKHUNGU WASWA 195
  • • The adult worm consists • of a scolex (head) that is about 1 mm in size • and lacks hooks but has four sucking discs. Behind • the scolex is the generative neck, which • segments to form the strobila composed of proglottids. WALTER WAKHUNGU WASWA 196
  • • fully developed embryos, and may survive for • months. When the eggs are ingested by herbivores, • such as cattle, the embryos are released, • penetrate the intestinal wall, and are carried to • striated muscles where they are transformed • into larval forms designated cysticerci. WALTER WAKHUNGU WASWA 197
  • • Symptoms, Diagnosis, and Treatment • Most cases of taeniasis are asymptomatic regardless • ofthe Taenia species involved, but symptoms • differ when humans serve as intermediate • host. WALTER WAKHUNGU WASWA 198
  • • ROUNDWORMS • The disease-causing roundworms of primary • importance in foods belong to two orders ofthe • phylum Nematoda. WALTER WAKHUNGU WASWA 199
  • • • • • • • Phylum Nematoda Class Adenophorea (= Aphasmidia) Order Trichinellida Genus Trichinella Class Secernentea (= Phasmidia) Order Rhabditida WALTER WAKHUNGU WASWA 200
  • • Trichinosis • Trichinella spiralis is the etiological agent of • trichinosis (trichinellosis), the roundworm disease • of greatest concern from the standpoint of • food transmission. WALTER WAKHUNGU WASWA 201
  • • the trichinae are transmitted from host • to host; no free-living stages exist. In other words, • both larval and adult stages of T. spiralis are • passed in the same host. It is contracted most • often from raw or improperly cooked pork • products. WALTER WAKHUNGU WASWA 202
  • • Although they • may remain in the intestines for about a month, • no symptoms are produced. WALTER WAKHUNGU WASWA 203
  • • As the larvae burrow into muscles several weeks later, severe pain, fever, and other symptoms occur, which sometimes lead to death from heart failure (see below). WALTER WAKHUNGU WASWA 204
  • Symptoms and Treatment One to 2 days after the ingestion of heavily encysted meat, trichinae penetrate the intestinal mucosa, producing nausea, abdominal pain, diarrhea,and sometimes vomiting. WALTER WAKHUNGU WASWA 205
  • Diagnosis • Because the trichinae exist as coiled larvae in • ovoid capsular cysts in skeletal muscles, biopsies • are sometimes performed on the deltoid, biceps, • or gastrocnemius muscles. WALTER WAKHUNGU WASWA 206
  • Prevention and Control • Trichinosis can be controlled by avoiding the • feeding of infected meat scraps or wild game • meats to swine and by preventing the consumption • of infested tissues by other animals. WALTER WAKHUNGU WASWA 207