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Environmental microbiology
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Environmental microbiology


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  • 2. Microbiology of Food  Transmission of gastrointestinal infections is usually a result of ingestion of contaminated food or water  Under usual conditions, the gut flora maintains a harmless relationship with the host  Gastrointestinal infections result from organisms that are able to survive the harsh conditions of the stomach and competition with the microbial flora and to produce damage to the tissues of the gastrointestinal tract Company LogoCompany Logo
  • 3. Microbiology of Food Food bacteriology is focused on :  spoilage  diseases transmission  Food and dairy products may be contaminated in a variety of ways and from a variety of sources:  Soil and water: Alcaligenes, Bacillus, Citrobacter, Clostridium, Pseudomonas, Serratia, Proteus, Enterobacter, and Micrococcus  Food utensils: depends on the type of food and the manner in which the utensils were handled Company LogoCompany Logo
  • 4. Microbiology of Food Enteric microorganisms of humans and animals: Bacteroides, Lactobacillus, Clostridium, Escherichia, Salmonella, Proteus, Shigella, Staphylococcus, and Streptococcus Food handlers: Staphylococcus, which is generally found on hands and skin, and in the upper respiratory tract Animal hides and feeds: Microorganisms found in water, soil, feed, dust, and fecal debris can be found on animal hides Company LogoCompany Logo
  • 5. Microbiology of Food Food poisoning :  is restricted to infection by enteric pathogen contaminating food, or  Ingestion of food containing exotoxins produced by bacteria Mycotoxins :  many fungi produce poisonous substances (mycotoxins)  cause serious or fatal diseases if ingested  The mycotoxins of important to human : • toxin of the poisonous mushroom • aflatoxin Company LogoCompany Logo
  • 6. Microbiology of Food Aflatoxins:  are produced by Aspergillus flavus  They are highly toxic and carcinogenic  May cause cirrhosis & cancer of the liver Control bacteria in food–prevention of spoilage :heating, sugar, drying, acids, Salting, low temperature, Smoking, irradiation, Chemical preservation Control of bacteria in food–prevention of diseases transmission :  Preventable only by rigid sanitation control and improve personal hygiene  Company LogoCompany Logo
  • 7. Microbiology of Food Organisms that can cause disease by means of a preformed toxin include Clostridium botulinum, Bacillus cereus, and S. aureus. The severity of disease ranges from a mild diarrhea to a rapidly fatal intoxication. Food poisoning by B.cereus and S. aureus is relatively common and is self- limiting. Botulism, caused by C. botulinum, although rare, can be life- threatening Company LogoCompany Logo
  • 8. Microbiology of Food A commonly seen cause of the diarrhea and intestinal infection is E. coli. This organism is a member of the intestinal flora; however, some strains of E. coli produce cytotoxins that cause alterations in the biochemical activity of the intestinal epithelial cells, resulting in problems with fluid and electrolyte control by the intestinal cells. Three strains of E. coli, referred to as enterotoxigenic, are a common cause of “traveler diarrhea” and other intestinal problems Company LogoCompany Logo
  • 9. Microbiology of Food the classic intestinal pathogen is Vibrio cholerae, the cause of cholera. This organism produces an enterotoxin that causes the outpouring of fluid from the cells into the lumen of the intestine. Massive amounts (up to 20 L per day) can be lost. Other intestinal pathogens are Clostridium difficile, Shigella spp., Aeromonas hydrophila, Campylobacter jejuni, and Salmonella spp Company LogoCompany Logo
  • 10. Microbiology of Food A number of viruses also cause diarrheal disease Viral agents in this category include hepatitis, rotavirus, adenovirus, coxsackievirus, and Norwalk-like agents Numerous parasites, such as Fasciolopsis buski, Giardia lamblia, Entamoeba histoyitica, and Balantidium coli, also infect the gastrointestinal Company LogoCompany Logo
  • 11. Microbiology of Food By enumerating microorganisms in milk and foods, the quality of a particular sample can be determined. Although the microorganisms cannot be identified, the presence of a high number suggests a good possibility that pathogens may be present. Even if a sample contains a low microbial count, it can still transmit infection. Company LogoCompany Logo
  • 12. Methods of Study Coliform analysis is carried out on food samples as well as on water and milk to determine whether fecal contamination has occurred. Meat: The surface, becomes contaminated from dust or from handling immediately upon dismemberment of the animal Ground Meat: The grinding process intro- duces the surface contaminants into the interior of the meat and may also warm the meat enough to encourage considerable bacterial multiplication Company LogoCompany Logo
  • 13. Methods of Study Fish: bacterial population will include many marine halophilic and psychrophilic forms Shellfish: gathered near a sewage outlet will contain numbers of sewage bacteria, including both pathogenic enterobacteria and viruses. Fruits and Vegetables: Most vegetables have a considerable surface contamination of soil organisms. Fruits acquire a surface flora through dust contamination and handling. Company LogoCompany Logo
  • 14. Methods of Study Eggs :The surface becomes contaminated immediately after laying, but penetration of the egg by bacteria is normally prevented by a dry, mucilaginous coating on the surface Bread : Baking kills most microorganisms, but spores of bacilli, clostridia, and fungi persist and will germinate to produce a new flora unless preservatives are added. Company LogoCompany Logo
  • 15. Microbiology of Water With increasing industrialization, water sources available for consumption and recreation have been adulterated with industrial as well as animal and human wastes Polluted waters contain vast amounts of organic matter that serve as excellent nutritional sources for the growth and multiplication of microorganisms The presence of pathogenic microorganisms in water indicates contamination Company LogoCompany Logo
  • 16. Microbiology of Water  These pathogens are responsible for intestinal infections such as bacillary dysentery, typhoid fever, cholera, and paratyphoid fever  Analysis of water samples on a routine basis would not be possible if each pathogen required detection. Therefore water is examined to detect Escherichia coli, the bacterium that indicates fecal pollution  Pathogenic microorganisms reach the water from :  Soil  Human excrement  Bodies/ animal who have died of infectious diseases Company LogoCompany Logo
  • 17. Microbiology of Water Waterborne diseases may be acquired by:  drinking contaminated water  washing utensil  eating shellfish Control of bacteria in water:  sanitation of drinking water  sanitation of swimming pool  purification of sewage Company LogoCompany Logo
  • 18. Microbiology of Water Sanitation of drinking water:  drinking water supplies may become contaminated  Can cause an epidemic of enteric diseases  Water supplies usually filtered & chlorinated Filtration of water supplies:  trough beds of sands  chlorinated by chlorine : 0,5 ppm will rid the water of enteric pathogen Company LogoCompany Logo
  • 19. Microbiology of Water Sanitation of swimming pools:  by chlorination, 0,5 ppm of free chlorine  Coliform bacteria are used as indicator of pollution  Staphylococcus of human origin persist longer than coliform in chlorine – treated water Sewage Purification  Screening-Bulky  nondecomposable material is screened and removed (bottles, paper, boxes, etc).  Sludge formation  The screened sewage is allowed to settle in large tanks. The sediment, containing much of the organic matter and microorganisms, is called sludge. Company LogoCompany Logo
  • 20. Microbiology of Water  Sludge digestion  The sludge obtained by either process described above consists of organic matter rich in bacteria and other microbes  Disposal of supernatant  The supernatant, after chlorination, may be pumped into a large body of water. Company LogoCompany Logo
  • 21. Methods of Study A. Quantitative Analysis the method employed is plate count (viable count) by a serial dilution of water Each dilution tube is plated in nutrient agar The resulting colonies counted Company LogoCompany Logo
  • 22. Example of a viable count Company LogoCompany Logo Dilution Plate Count* Undiluted Too crowded 10-1 To count 10-2 510 10-3 72 10-4 6 10-5 1 The 10The 10-3-3 dilution has a suitabledilution has a suitable number of colonies, the others beingnumber of colonies, the others being either too high or too low for accuracy.either too high or too low for accuracy. The original water sample is calculatedThe original water sample is calculated to have contained 72,000(72 x 10to have contained 72,000(72 x 1033 )) viable cells per mL.viable cells per mL.
  • 23. Qualitative analysis :  to obtain a picture of the aquatic bacterial population  The method are :  tube method  Dilutions of a water sample are inoculated into tubes of a medium which is selective for coliform bacteria and in which all co-liform bacteria but few noncoliform bacteria will form acid and gas.  membrane filtration method  A large measured volume of water is filtered through a sterilized membrane of a type that retains bacteria on its surface while permitting the rapid passage of smaller particles and water.  Both qualitative and quantitative methods are used to determine the sanitary condition of water Company LogoCompany Logo