Concise description on various aspects of Food Microbiology and importance in Medical Microbiolgy and healthcare for Medical PG Students, Medical UG Students, Nursing students.

1. Microbiology of Food
Dr.
Suprakash
Das

2. Food Microbiology-Introduction
 Food microbiology is specifically concerned with the desirable and
undesirable effects microbes can have on the quality and safety of food
products.
 Almost all foods harbor one or more types of microorganisms. Some of
them play desirable roles in food, such as in the production of naturally
fermented foods,
 whereas others cause food spoilage and food borne diseases.
 To study the role of microorganisms in food and to control them when
necessary, it is important to
 Isolate them in pure culture and
 Study their morphological, physiological, biochemical, and genetic
characteristics.
 The major developments of ideas on the possible roles of microorganisms
in foods and their scientific proof were initiated by Pasteur in the 1870s,
followed by many other scientists before the end of the 19th century.
 This paved the way for the establishment of early food microbiology in
the 20th century.

6. Food Microbiology: Current Status
 In the early 20th century, studies continued to understand the association
and importance of microorganisms, especially pathogenic bacteria in food.
 Their isolation and identification.
 The importance of sanitation in the handling of food
 Prevent growth as well as to destroy the spoilage and pathogenic bacteria.
 Isolating beneficial bacteria associated with food fermentation
 However, after the 1950s, food microbiology entered a new era.
 Diverse types of food; microbial interactions in food environments
 Microbial physiology, biochemistry, genetics, and immunology has helped
open new frontiers in food microbiology.
 Now, understanding the microbial community and microbial interaction in
a complex food environment through
 Microbiome analysis,
 Whole genome sequencing, and
 Development of novel and natural intervention technologies are at the
forefront of food microbiology.

7. Food Microbiology: Current Status
Food Fermentation/Probiotics-
 Development of strains with desirable metabolic activities by
genetic transfer among strains
 Development of bacteriophage-resistant lactic acid bacteria
 Metabolic engineering of strains for overproduction of desirable
metabolites
 Development of methods to use lactic acid bacteria to deliver
biologically relevant proteins or vaccines
 Sequencing genomes of important lactic acid bacteria and
bacteriophages for better understanding of their characteristics
 Food biopreservation with desirable bacteria and their antimicrobial
metabolites
 Understanding of important characteristics of probiotic bacteria and
development of desirable strains
 Effective methods to produce starter cultures for direct use in food
processing
 Bioengineered probiotics for health promotion and disease control

8. Food Microbiology: Current Status
Food Spoilage-
 Identification and control of new spoilage bacteria
associated with the current changes in food processing
and preservation methods
 Spoilage resulting from bacterial enzymes of frozen
and refrigerated foods with extended shelf life
 Development of molecular methods, including
nanotechnology, to identify metabolites of spoilage
bacteria and predict the potential shelf life of foods
 Importance of environmental stress on the resistance of
spoilage bacteria to antimicrobial preservatives
 Microbial community, ecology, and quorum sensing in
food

9. Food Microbiology: Current Status
Foodborne Diseases
 Methods to detect emerging foodborne pathogenic bacteria from
contaminated foods
 Application of molecular biology techniques, including
nanotechnology and biotechnology, for rapid detection of
pathogenic bacteria in food and the environment
 Effective detection and control methods of foodborne
pathogenic viruses
 Transmission potentials of prion diseases from food animals to
humans
 Importance of environmental stress on the detection and
destruction of pathogens
 Factors associated with the increase in antibiotic-resistant
pathogens in food
 Biofilm formation, microbial quorum sensing, and attachment of
foodborne pathogens to food and equipment surfaces

10. Food Microbiology: Current Status
 Mechanisms of pathogenicity of foodborne
pathogens
 Effect of food or environment-related stress on gene
regulation, pathogenicity, and survival
 Effective methods for the epidemiological study of
foodborne diseases: Genome-based approaches to
study epidemiology, including whole genome
sequence and molecular fingerprinting techniques
 Application of bacteriophages and other natural
antimicrobials for control of foodborne pathogens
Control of pathogenic parasites in food
Mold and mycotoxin detection and control
Fish and shellfish toxin detection and control
Foodborne disease control strategies in pre-harvest (on
farms) and postharvest food production.

11. Food Microbiology: Current Status
Foodborne Diseases
 The discipline also includes basic information of microbial
ecology, physiology, metabolism, and genetics.
This information is helping to develop methods for-
 Rapid and effective detection of spoilage and pathogenic
bacteria,
 To develop desirable microbial strains by recombinant DNA
technology, to produce fermented foods of better quality,
 To develop thermostable enzymes in enzyme processing of
food and food additives,
 To develop methods to remove bacteria from food and
equipment surfaces, and
 To combine several control methods for effective control of
spoilage and pathogenic microorganisms in food.

13. Important Bacterial Groups in Foods
 Among the microorganisms found in foods, bacteria constitute major
important groups BECAUSE -
 many different species can be present in foods
 rapid growth rate,
 ability to utilize food nutrients, and
 ability to grow under a wide range of temperatures,
 aerobiosis, pH, and water activity as well as
 survive adverse situations, such as survival of spores at high
temperatures.
 For convenience, bacteria important in foods have been arbitrarily divided
into several groups on the basis of similarities in certain characteristics.
Lactic Acid Bacteria
• These bacteria produce relatively large quantities of lactic acid from
carbohydrates. Species mainly from genera
• Lactococcus,
• Leuconostoc,
• Pediococcus,
• Lactobacillus, and
• Streptococcus thermophilus are included in this group.

14. Important Bacterial Groups in Foods
Acetic Acid Bacteria
• These are bacteria that produce acetic acid, such as Acetobacter aceti.
Propionic Acid Bacteria
• These bacteria produce propionic acid and are used in dairy fermentation.
Species such as Propionibacterium freudenreichii are included in this
group.
Butyric Acid Bacteria
• These bacteria produce butyric acid in relatively large amounts. Some
Clostridium spp., such as Clostridium butyricum, are included in this
group.
Proteolytic Bacteria
• These bacteria can hydrolyze proteins because they produce extracellular
proteinases. Species in genera Micrococcus, Staphylococcus, Bacillus,
Clostridium, Pseudomonas, Alteromonas, Flavobacterium, Alcaligenes,
some in Enterobacteriaceae, and Brevibacterium are included in thi
group.
Lipolytic Bacteria
• These bacteria hydrolyze triglycerides because they produce extracellular
lipases. Species in genera Micrococcus, Staphylococcus, Pseudomonas,
Alteromonas, and Flavobacterium are included in this group.

15. Important Bacterial Groups in Foods
 Saccharolytic Bacteria- hydrolyze complex carbohydrates. Species in genera
Bacillus, Clostridium, Aeromonas, Pseudomonas, and Enterobacter are included
in this group.
 Thermophilic Bacteria- grow at 50°C and above. Species from genera Bacillus,
Clostridium, Pediococcus, Streptococcus, and Lactobacillus are included in this
group.
 Psychrotrophic Bacteria- grow at refrigerated temperature (≤5°C). Some species
from Pseudomonas, Alteromonas, Alcaligenes, Flavobacterium, Serratia,
Bacillus, Clostridium, Lactobacillus, Leuconostoc, Carnobacterium, Brochothrix,
Listeria, Yersinia, and Aeromonas are included in this group.
 Thermoduric Bacteria- survive pasteurization temperature treatment. Some
species from Micrococcus, Enterococcus, Lactobacillus, Pediococcus, Bacillus
(spores), and Clostridium (spores) are included in this group.
 Halotolerant Bacteria- survive high salt concentrations (≥10%). Some species
from Bacillus, Micrococcus, Staphylococcus, Pediococcus, Vibrio, and
Corynebacterium are included in this group.
 Aciduric Bacteria- survive at low pH (<4.0). Some species from Lactobacillus,
Pediococcus, Lactococcus, Enterococcus, and Streptococcus are included in this
group.

16. Important Bacterial Groups in Foods
 Facultative Anaerobes- These are bacteria that are able to grow in
both the presence and absence of oxygen. Lactobacillus,
Pediococcus, Leuconostoc, enteric pathogens, and some species of
Bacillus, Listeria, Salmonella, Serratia, and coliforms are included
in this group.
 Coliforms- Species from Escherichia, Enterobacter, Citrobacter,
and Klebsiella are included in this group. They are used as an index
of sanitation.
 Fecal Coliforms- Mainly Escherichia coli is included in this group.
They are also used as an index of sanitation.
 Enteric Pathogens- Pathogenic Salmonella, Shigella,
Campylobacter, Yersinia, Escherichia, Vibrio, hepatitis A, and
others that can cause gastrointestinal infection are included in this
group. Because of the importance of these bacterial groups in food,
many laboratory methods are designed to detect a specific group
instead of a specific genus or species. Similarly, control methods are
sometimes designed to destroy or prevent growth of a specific
group.

18. Factors Affecting Microbial Growth
Like all other living organisms, bacteria require
favorable environment to live and grow.
There are six basic environmental factors that
impact bacterial growth. An easy way to
remember these conditions is to use the memory
device FAT TOM
F= Food composition
A= Acidity
T= temperature
T=Time
O= Oxygen
M= Moisture

19. Factors Affecting Microbial Growth
 Food Composition
 A suitable supply of nutrients is the most important condition affecting
growth of bacteria.
 These include solutions of sugars or other carbohydrates, proteins, and
small amounts of other materials such as phosphates, chlorides and
calcium.
 Acidity
 The pH of a meat or poultry product can have a profound effect on the
growth and viability of microbial cells. Each species of microbe grows
within an optimal range of pH values.
 Most microbes thrive when the pH is near neutral or slightly acidic, but
there are exceptions.
 Most bacteria will not grow at pH levels below 4.6 because the
environment is too acidic.
 Many molds and yeasts can grow at a lower pH than do bacteria.
 Meat with a pH in the 6.0 to 6.4 range spoils faster than meat in the lower
pH range of 5.3 to 5.7, because spoilage microbes are more active in the pH
range of 6.0 to 6.4.

21. Factors Affecting Microbial Growth
Temperature
 All bacteria, molds, and yeasts have an optimum, maximum, and minimum
temperature for growth.
 These temperatures can vary among different species of microbes.
Therefore, environmental temperature not only impacts the rate of growth
of microbes but can determine which microbial species thrive.
 A temperature difference of only a few degrees may favor the growth of an
entirely different population of microbes.
 Below approximately 41°F proliferation of spoilage microbes is slow,
and growth of most pathogenic microbes stops.
 Listeria monocytogenes (Lm), a bacterial pathogen of concern in many
ready-to-eat products, is a notable exception. While Lm grows optimally
at temperatures in the range of 86 to 98.6°F, it is capable of growing at a
temperature as low 31.3°F.
 At temperatures above 140°F most microbes begin to die,
 In food processing, the temperature range of 41 – 140°F is commonly
referred to as the danger zone, because the optimum, maximum, and
minimum temperature for growth of most microbes will fall somewhere
within that range.
 However, it is important to note that time is a major factor associated with
the rate of growth at a particular temperature.

22. Factors Affecting Microbial Growth
Time
 Permitting sufficient time for microbes to adapt to their
environment (lag phase) is necessary before they can enter
the rapid growth phase (log phase).
 The doubling time for most bacterial species is between 10-
30 minutes under optimal conditions for growth.
 Bacteria would grow much more slowly in meat and poultry
products, especially if those products are properly handled
and stored.
 Allowing the temperature of meat and poultry products to
remain in the danger zone for a sufficient period of time
will promote significant proliferation of microbes and
microbial toxins.

23. Factors Affecting Microbial Growth
Oxygen
 Similar to temperature, oxygen availability can determine which microbes
will be active.
 Microbes that have an absolute requirement for oxygen are called obligate
aerobes.
 Those that require the total absence of oxygen are called obligate
anaerobes.
 Some microbes are called facultative anaerobes, because they can grow in
the presence or absence of oxygen.
 Molds require oxygen for growth.
 Yeasts grow best under aerobic conditions, but some can grow slowly
under anaerobic conditions.
 The kinds of bacteria that cause food spoilage tend to be aerobes, but those
that cause foodborne illness are anaerobes or facultative anaerobes.

24. Factors Affecting Microbial Growth
Moisture
 The availability of water in a food (referred to as water activity, or
aw) is an important factor for microbial growth.
 Nutrients for microbial growth must be in a soluble form for
microbes to utilize them.
 Generally, bacteria have the highest aw requirements,
 molds have the lowest, and yeasts are intermediate.
 Most moist food products will have greater water availability to
support microbial growth than dryer food products, but there are
exceptions.
 For example, some processing methods might incorporate certain
chemical ingredients (e.g., salt) that bind to free water and in
sufficient concentrations significantly reduce aw limiting the growth
of some microbes.

25. Microbes and Food Spoilage
 Spoilage is caused by physical and chemical changes in food products that
result in undesirable odors, flavors, textures, or colors.
 There are three primary mechanisms that can result in spoilage of meat and poultry
products
 Autolytic enzymatic spoilage,
 Lipid oxidation,
 Microbial spoilage.
Microbes can cause food spoilage by two basic mechanisms.
 The most important mechanism is related to the growth of spoilage microbes
and their active metabolism of food components.
 As microbes die, they can release various enzymes that react with and change
properties of food components, leading to spoilage.
 Bacteria and yeasts typically result in slime formation, bad odors, rancid flavors,
and discoloration (grey, brown, or green).
 Anaerobic spoilage bacteria, which can be an important in vacuum packaged
products, can produce a distinctive souring.
 Molds often result in a stickiness of the product surface and eventually the
formation of creamy, black, or green colonies with a fuzzy appearance.

26. Important Facts in Foodborne Diseases
1. Ingestion of toxins naturally present in many foods. This includes
certain mushrooms, some fruits and vegetables, and some seafoods.
2. Toxins formed in some foods. Examples are some biological amines
(e.g., histamine) that form in some fish, cheeses, and fermented
meat products as a result of breakdown of proteins by bacterial
proteases.
3. The presence of toxic chemicals in contaminated food and water,
such as heavy metals and some pesticides.
4. Allergy to some normal components of a food. There are individuals
who are allergic to gluten in cereals and develop digestive disorders
(celiac disease) following consumption of food containing gluten.
5. Genetic inability to metabolize normal food components. The
inability of some individuals to hydrolyze lactose in the small
intestine because of the lack of production of enzyme lactase results
in digestive disorders (lactose intolerance).
6. Nutritional disorders, such as rickets from calcium deficiency.
7. Indigestion from overeating or other reasons.

35. Foodborne Intoxications
 Foodborne intoxication or food poisoning of microbial origin occurs
from the ingestion of a food containing a preformed toxin from
bacteria, such as Staphylococcus aureus, Bacillus cereus, and
Clostridium botulinum, and mycotoxin from mold. Some genera
characteristics of food poisoning include the following:
1. The toxin is produced by a pathogen while growing in a food.
2. A toxin can be heat labile or heat stable.
3. Ingestion of a food containing an active toxin, not viable microbial
cells, is necessary for poisoning (except for infant botulism or
hidden botulism, in which viable spores need to be ingested).
4. Symptoms generally occur quickly, as early as 30 minutes after
ingestion.
5. Symptoms differ with the type of toxin ingested; enterotoxins
produce gastrointestinal symptoms, and neurotoxins produce
neurological symptoms.
6. The febrile symptom is not present.

36. Staphylococcal Intoxication
 Staphylococcal food poisoning (also known as staphylococcal
gastroenteritis, staph food poisoning), caused by toxins of
Staphylococcus aureus,
 is considered to be one of the most frequently occurring foodborne
diseases worldwide.
 Enterotoxigenic strains of Sta. aureus produce 21 different
enterotoxins: A, B, C1, C2, C3, D, and E through V (also
designated as SEA, SEB, etc.).
 Toxins are produced when the food, primarily protein-rich food, is
left at room temperature for long periods. The toxins vary in heat
stability.
 Upon consumption, the toxin stimulates the vagus nerve in the
stomach and induces severe vomiting.
 The symptoms occur within two to four hours with a range of 30
minutes to eight hours and are directly related to the potency and
amounts of toxin ingested and an individual’s resistance.
 The disease lasts for about one to two days and is rarely fatal.

38. Botulism by Clostridium botulinum
 Foodborne botulism results following consumption of food
containing the potent botulinum toxin of Clostridium botulinum.
 It is a neurotoxin and produces neurological symptoms along with
some gastric symptoms.
 Unless prompt treatment is administered, it is quite fatal.
 The botulinu neurontoxin (BoNT) is a 150 kDa protein toxin
produced by Clo. botulinum. It is an A-B type toxin consisting of
two subunits: A subunit is 50 kDa, and B is 100 kDa.
 In general, toxins associated with food intoxication in humans
(types A, B, E, and F) are extremely potent,
 A subunit has endopeptidase (metalloprotease) activity that cleaves
syneptobrevin, a protein that controls the release of
neurotransmitter acetylcholine in the neuromuscular junction,
thereby interfering with the flow of nerve impulses.
 This results in irreversible flaccid paralysis of all involuntary
muscles. The toxin moves slowly through the body.

42. Pathogenic Escherichia coli
They are subdivided into six groups based on
their ability to produce toxins and to adhere to
and to invade epithelial cells. They are
enterotoxigenic Esc. coli (ETEC),
enteropathogenic Esc. coli (EPEC),
enteroinvasive Esc. coli (EIEC),
enterohemorrhagic Esc. coli (EHEC),
enteroaggregative Esc. coli (EAEC), and
diffuse-adhering Esc. coli (DAEC).

43. Shigella Species
 Shi. dysenteriae is responsible for a brisk but deadly epidemic
outbreak,
 Shi. flexneri and Shi. sonnei cause endemic disease, and Shi. boydii
causes rare disease.
 Only humans and some primates serve as their hosts.
 The organisms are either transmitted directly through fecal-oral
routes or indirectly through fecal-contaminated food and water.
 Once engulfed by the epithelial cells, they produce an exotoxin that
has an enterotoxigenic property- Shiga toxin (Stx).
 The symptoms occur in 12 hours to seven days but generally in one
to three days.
 In case of mild infection, symptoms last for five to six days, but in
 severe cases, symptoms can linger for two to three weeks.
 Abdominal pain,
 Diarrhea often mixed with blood, mucus and pus,
 Fever,
 Chills, and headache.

44. Salmonella enterica
 Foodborne salmonellosis is characterized by gastrointestinal disorders
manifested predominantly by diarrhea and abdominal cramp.
 A dose of >102–3 cells is needed to be consumed to initiate infection.
 Following ingestion, the pathogen colonizes in the small and large
intestines, and most of the pathological lesions are reported to be found in
the large intestine rather than in the small intestine.
 Bacteria can also enter through M cells in Peyer’s Patch, a localized
lymphoid tissue in the small intestine.
 Salmonella multiplies inside epithelial cells and macrophages, neutrophils,
and eventually lyses the cells.
 As a result, inflammation and severe edema occur in the site of infection
and lead to mucosal damage.
 The symptoms appear within eight to 42 hours, generally in 24–36 hours.
 The symptoms last for about two to three days but, in certain individuals,
can linger for a long time.
 An individual remains in a carrier state for several months following
recovery.

46. Listeria monocytogenes
 Listeria monocytogenes causes two forms of diseases:
(1) febrile gastroenteritis and
(2) invasive systemic diseases.
 Febrile Gastroenteritis- This form is mostly associated with healthy
individuals, and the infectious dose is in the range of 108–1010 cells.
 Most often, the symptoms appear within one to seven days
following ingestion and include mild flu-like symptoms with
slight fever, abdominal cramps, and diarrhea. The symptoms
subside in a few days, but the individual sheds Lis. monocytogenes
in the feces for some time.
 Invasive Systemic Disease. This form of disease is associated with
immunologically challenged populations.
 These groups include
 pregnant women,
 unborn fetuses,
 infants, elderly people
 steroids and chemotherapeutic agents.

47. Listeria monocytogenes
 The infective dose in these people is considered to be about 100–1000 cells.
 The incubation period for invasive disease is about two to three weeks before the
symptoms are visible.
 Symptoms include bacteremia (septicemia) resulting in fever and headache,
meningitis, encephalitis, endocarditis, liver abscess, and others.
 The fatality rate among fetuses, infected newborn infants, and
immunocompromised individuals is very high.
 Foodborne listeriosis in humans is mainly sporadic; however, outbreaks were
reported from the consumption of
 contaminated coleslaw,
 pasteurized milk,
 raw milk and dairy products, soft cheeses (Mexican style, Brie, and
Liederkranz),
 meat pate, turkey franks,
 cold cut meats,
 improperly cooked chicken, and smoked mussels.
 Fruits and vegetables, including celery and cantaloupes.

49. Campylobacter Species
 The infective dose for campylobacteriosis is considerably low, only
approximately 500 cells.
 Following ingestion, motile bacteria reach the mucus layer.
 Toxin production causes cell damage (death), inflammation, and
fluid loss resulting in diarrhea that appears in two to five days.
 Symptoms generally last for two to three days but can linger for two
weeks or more
 The main symptoms are enteric and include
 abdominal cramps,
 profuse diarrhea, nausea, and
 vomiting.
 Other symptoms include
 fever,
 headache, and chills.
 In some cases, bloody diarrhea.
 Guillain-Barre syndrome, a debilitating generalized paralysis.
 Reiter’s syndrome.

50. Campylobacter Species
 Cam. jejuni has been isolated at a very high frequency from
 raw meats (beef, lamb, pork, chicken, and turkey),
 milk,
 eggs,
 vegetables,
 mushrooms, and
 clams.
 In heat-processed food, their presence has been related to cross-contamination
following heat treatment or to improper heating.
 The use of animal feces as fertilizers was found to contaminate vegetables.
 Outbreaks of campylobacteriosis result from the consumption of raw milk,
 improperly cooked chicken,
 dairy products,
 bakery products,
 turkey products,
 Chinese food,
 eggs, and others.
 Consumption of raw milk and chicken were implicated in many outbreaks.

51. Yersinia enterocolitica
 Foods that are incriminated for yersiniosis are generally cycled
through refrigeration.
 Generally, a high dose (>104 cells) is required for the disease.
 In the intestine, the enterotoxin Yst promotes fluid secretion,
resulting in diarrhea.
 Young children are more susceptible to foodborne yersiniosis.
 Symptoms are
 severe abdominal pain at the lower quadrant of the abdomen
mimicking appendicitis,
 diarrhea,
 nausea,
 vomiting, and
 fever.
 Symptoms generally appear 24–30 hours following consumption of
a contaminated food and last two to three days.

52. Yersinia enterocolitica
Immunocompromised hosts
 septicemia,
 pneumonia,
 meningitis,
 endocarditis, and so forth.
 Long-term sequelae of yersiniosis is manifested as
 reactive arthritis and erythema nodosum.
It has been isolated from
 raw milk,
 processed dairy products,
 raw and improperly cooked meats,
 chitterling,
 fresh vegetables, and
 improperly chlorinated water.
Foods implicated in yersiniosis include
 raw and pasteurized milk,
 ice cream, and
 improperly cooked meats.

53. Vibrio parahaemolyticus
 Generally, an individual has to consume 105–7 cells of a Kanagawa-positive
strain for symptoms to develop.
 Symptoms appear 10–24 hours following ingestion of live cells and last for two
to three days.
Symptoms include
 nausea,
 vomiting,
 abdominal cramps,
 watery diarrhea,
 headache, fever, and chills.
 Sometimes, bloody diarrhea.
 Systemic spread of the organism in blood may lead to septicemia resulting in
organ failure, shock, and death.
The outbreaks, as well as sporadic cases -consumption of
 raw, improperly cooked, or post-heat-contaminated seafoods, including
 fish (mackerels, sardines, codfish),
 oysters, crabs, shrimp, clams, octopus, and lobsters.

54. Clostridium perfringens
 Once the enterotoxin (CPE) is produced in the intestinal lumen, it binds to
claudin protein (receptor) in the tight junction on intestinal epithelial cells,
resulting in loss of water, Na+, and Cl–.
 The enterotoxin causes only gastroenteritis.
 CPE also causes epithelial cell death and leads to damage in microvilli, epithelial
sloughing, and necrosis, further triggering fluid and electrolyte loss.
 The symptoms appear 8–24 hours following ingestion of a large number of viable
cells (≥5 × 105/g) through a food.
The main symptoms are
 diarrhea and
 abdominal pain.
 Nausea, vomiting, and fever
 Symptoms generally disappear within 24 hours.
 The foods commonly incriminated with the outbreaks include
 meat stews (beef and poultry), roasts, meat pies,
 casseroles, gravies, sauces,
 bean dishes, and some Mexican foods (tacos and enchiladas).

56. Bacillus cereus
 In general, a large number of cells (106–108/g) need to be ingested to
produce gastroenteritis.
 Two types of enterotoxins produce two types of symptoms.
 Emetic toxin is also called cereulide and is responsible for severe
vomiting resembling staphylococcal food poisoning.
 The mode of action for the diarrheagenic toxin is not well understood, but
it induces diarrhea by stimulating the cAMP system.
 In the diarrheal form, symptoms occur 6–12 hours following consumption
of a food containing the viable cells.
Symptoms include
 abdominal pain,
 profuse watery diarrhea, and perhaps nausea,
 but no vomiting or fever.
 Recovery is usually within 24 hours.
In the diarrheal outbreaks, a variety of foods, including
 vegetables, salads,
 meats, pudding, casseroles, sauces, and soups, has been implicated, mostly
because of their improper cooling.
 However, in the emetic form, outbreaks mostly involve rice, pasta, and
sometimes other starchy foods.

60. Control of Access of Microorganisms: Cleaning, Sanitation,
and Disinfection
 The main objective of sanitation is to minimize the access of microorganisms in food from
various sources at all stages of handling.
 Because the microbial sources and level of handling vary with each food of plant and animal
origin and fabricated foods, the methods by which microorganisms contaminate foods differ.
 Proper sanitation helps reduce the microbial load to desired levels in further processed food.
 Finally, proper sanitation helps reduce the incidence of foodborne diseases.
Factors to Consider-
 Plant design
 Quality of Water, Ice, Brine, and Curing Solution
 Quality of Air
 Training of Personnel
 Equipment
 Cleaning of Processing Facilities
Sanitation of Food-Processing Equipment
 Chlorine-Based Sanitizers
 Iodophores
 Quaternary Ammonium Compounds
Decontamination and Sanitization of Fruits and Vegetables
 Chlorine
 Ozone

61. Control by Physical Removal
Microorganisms can be physically removed from
solid and liquid foods by several methods.
In general, these methods can partially remove
microorganisms from food, and by doing so,
they reduce the microbial level and help other
antimicrobial steps that follow to become more
effective.
They are generally used with raw foods before
further processing.
Centrifugation
Filtration
Trimming
Washing

62. Control by Heat (Thermal Processing)
 The main objective (microbiological) of heating food is to destroy
vegetative cells and spores of microorganisms that include molds,
yeasts, bacteria, and viruses (including bacteriophages).
 Most foods are heated to destroy specific pathogens and some
spoilage microorganisms, which are important in a food.
 This is necessary in order to retain the acceptance and nutritional
qualities of a food.
 To control growth of surviving microorganisms in the food, other
control methods are used following heat treatment.
 Heating of foods also helps destroy undesirable enzymes (microbial
and food) that would otherwise adversely affect the acceptance
quality of food.
 Heating (warming) of ready-to-eat foods before serving is also
usually used to prevent growth of pathogenic and spoilage
microorganisms.
 A temperature above 50°C (122°F), preferably 60°C (140°F), is
important to control growth of many microorganisms in such foods
during storage before serving.

63. Control by Low Temperature
The main microbiological objective in low-temperature
preservation of food is to prevent or reduce growth of
microorganisms.
Low temperatures also reduce or prevent catalytic
activity of microbial enzymes, especially heat-stable
proteinases and lipases.
Germination of spores is also reduced.
Low-temperature storage, especially freezing (and
thawing), is also lethal to microbial cells,
Freezing is also used to preserve starter cultures for use
in food bioprocessing.
Ice Chilling
Refrigeration
Freezing

64. Control by Reduced Water Activity and Drying
 The main objective of reducing A W in food is to prevent or reduce
the growth of vegetative cells and germination and outgrowth of
spores of microorganisms.
 Prevention of toxin production by toxigenic molds and bacteria is
also an important consideration.
 Microbial cells (not spores) also suffer reversible injury and death in
foods with low A W although not in a predictable manner as in heat
treatment.
 Finally, reduced A W is also used to retain viability of starter-culture
bacteria for use in food bioprocessing.
 Natural Dehydration
 Mechanical Drying
 Freeze Drying
 Foam Drying
 Smoking
 Intermediate Moisture Foods

65. Control by Low pH and Organic Acids
The major antimicrobial objective of using weak
organic acids is to reduce the pH of food to control
microbial growth.
As the pH drops below 5.0, some bacteria become
injured and die.
However, the death rate in low pH is not predictable as
in the case of heat.
Acetic Acid
Propionic Acid
Lactic Acid
Citric Acid
Sorbic Acid
Benzoic Acid
Parabens (Esters of p-Hydroxybenzoic Acid)

66. Control by Modified Atmosphere (or Reducing O-R
Potential)
The objectives of MAP are to control or reduce the
growth of undesirable microorganisms in food.
The technique also helps retard enzymatic and
respiratory activities of fresh foods.
The growth of aerobes (molds, yeasts, and aerobic
bacteria) is prevented in products that are either
vacuum packaged or flushed with 100% CO2, 100%
N2, or a mixture of CO2 and N2.
However, under these conditions, anaerobic and
facultative anaerobic bacteria can grow unless other
techniques are used to control their growth.
Vacuum Packaging
Gas Flushing

67. Control by Antimicrobial Preservatives and Bacteriophages
 Antimicrobial chemicals are used in food in relatively small doses
either to kill undesirable microorganisms or to prevent or retard their
growth.
 They differ greatly in their abilities to act against different
microorganisms- (broad spectrum) or (narrow spectrum).
 Similarly, some compounds are effective against either gram-
positive or gram-negative bacteria or bacterial spores or viruses.
 Those capable of killing microorganisms are designated as
germicides (kill all types), fungicides, bactericides, sporicides, and
viricides, depending on their specificity of killing actions against
specific groups.
 Those that inhibit or retard microbial growth are classified as
fungistatic or bacteriostatic.
 However, under the conditions in which most antimicrobials are
used in foods, they cannot completely kill all the microorganisms or
prevent their growth for a long time during storage.

71. Control by Irradiation
 A food is irradiated because of the destructive power of ionization
on the microorganisms a food harbors.
 Depending on the method used, it can either completely or partially
destroy molds, yeasts, bacterial cells and spores, and viruses.
 In addition, irradiation can destroy worms, insects, and larvae in
food.
 It also prevents the sprouting of some foods, such as potatoes and
onions.
 However, irradiation cannot destroy toxins or undesirable enzymes
in a food;
 Irradiation is a cold sterilization process in as much as the
temperature of a food does not increase during treatment, and thus
irradiated foods do not show some of the damaging effects of heat
on food quality.
 However, irradiation can cause oxidation of lipids and denaturation
of food proteins, especially when used at higher doses.

73. Control by Novel Processing Technologies
Microwave and Radio-Frequency Processing
Ohmic and Inductive Heating
Infrared Heating
Pulsed Electric Fields
High-Pressure Processing
Pulsed Light Technology
Oscillating Magnetic Fields
Ultrasound
High-Voltage Arc Discharge
Pulsed X-Rays
Plasma Technology
Pulsed Electric Field
Hydrostatic Pressure Processing