FOOD MICROBIOLOGY
Microbial spoilage of foods – food borne
pathogens, food poisoning, food infection and
intoxication
Food borne diseases
 Safe, nutritious foods are essential to human health and well-
being.
 However, food-borne diseases pose a significant problem
worldwide.
 Food-borne diseases: are any illness resulting from the
consumption of food contaminated with one or more disease
producing agents.
 These include bacteria, parasite, viruses, fungi, and their
products as well as toxic substances not of microbial origin.
 These different diseases have many different symptoms, so
there is no one “syndrome” that is food borne illness.
 However, the microbe or toxin enters the body through the
gastrointestinal tract, and often causes the first symptoms
there, so nausea, vomiting, abdominal cramps and diarrhea is
common symptoms in many food borne diseases.
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Types of microbial food borne diseases:
 Foodborne
diseases in humans result from the
consumption of either food and water contaminated with
viable pathogenic bacterial cells (or spores in the case of
infant botulism) or food containing toxins produced by
toxigenic bacteria and molds.
 On the basis of mode of illnesses, Food borne diseases
can be divided into three groups:
 intoxication or poisoning,
 infection, and
 toxicoinfection.
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...Types of microbial food borne diseases
A. Intoxication
 Illness in this case occurs as a consequence of ingestion
of a pre formed bacterial or a mold toxin due to it
growth in a food.
 A toxin has to be present in the contaminated food.
 Once the microorganism have grown and produced toxin
in a food, there is no need of viable cells during the
consumption of the food for illness to occur. e.g,
Staphylococcal food poisoning and Botulism.
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...Types of microbial food borne diseases
B. Infection:
 Illness occurs as a result of the consumption of food and
water contaminated with enteropathogenic bacteria or
viruses.
 It is necessary that the cells of enteropathogenic bacteria
and viruses remain alive in the food or water during
consumption.
 Viable cells, even if present in small numbers, have the
potential to establish and multiply in the digestive tract to
cause the illness.
 Salmonellosis and hepatitis A are examples.
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...Types of microbial food borne diseases
C.Toxicoinfection:
 Illness occurs from ingesting a large number of viable cells of
some pathogenic bacteria through contaminated food and
water.
 Generally, the bacterial cells either sporulate or die and
release toxins to produce the symptoms.
 C. Perfringens gastroenteritis is an example.
 For toxicoinfection, viable cells should be consumed either in
very high numbers (for those that cannot multiply in the
digestive tract, such as C. perfringens) or in reasonable numbers
(for those that can multiply in the digestive tract, such as Vibrio
cholerae) so that toxins released by them in the digestive tract
can produce the symptoms.
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A. Foodborne Intoxications
INTRODUCTION

 Foodborne intoxication or food poisoning of microbial
origin occurs by ingesting a food containing a preformed
toxin.
 Two of bacterial origin, staphylococcal intoxication and
botulism, and mycotoxicosis of mold origin are briefly
discussed in this lecture.
 Although Bacillus cereus can also form a heat-stable toxin
and produce intoxication, this aspect is discussed under
toxicoinfection.
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... A. Foodborne Intoxications
Some general characteristics of food poisoning are:
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 active toxin, not viable microbial
cells, is necessary for poisoning (except for infant botulism, in
which viable spores need to be ingested).
4. Symptoms generally occur quickly, as early as 30 min after
ingestion.
5. Symptoms differ with type of toxin; enterotoxins produce
gastric symptoms and neurotoxins produce neurological
symptoms.
6. Febrile symptom is not present
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B. Foodborne Infections
 INTRODUCTION
 Foodborne infection occurs from the consumption of food
(and water) contaminated with pathogenic enteric bacteria
and viruses.
 The following are some characteristics of foodborne
infections:
1. Live cells of the enteric pathogens (bacteria and viruses)
have to be consumed through food.
2. The surviving cells (from gastric environment) penetrate
through the membrane and establish in the epithelial cells of
the intestines, multiply, and produce toxins (infection).
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... B. Foodborne Infections
3. Dose levels that cause infection vary greatly.
Theoretically, one live cell has the potential to produce
the disease. Experts estimate that consumption of 10 cells
(for an extremely virulent species and strain, such as
Escherichia coli O157:H7) to 105 cells or more (for a less
virulent species and strain, such as Yersinia enterocolitica)
might be required for the disease.
4. Symptoms generally occur after 24 h, which, depending
on the pathogen, and can be both enteric and nonenteric
in nature.
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... B. Foodborne Infections
5. Enteric symptoms are local and due to enteric infection
and the effect of toxins. Symptoms include abdominal
pain, diarrhea (sometimes accompanied with blood),
nausea, vomiting, and fever. Examples of pathogens include
Salmonella, Shigella, enteroinvasive E. coli (EIEC), Vibrio
parahaemolyticus, Campylobacter jejuni, and Y. enterocolitica.
6. Nonenteric symptoms (along with enteric symptoms)
result when the pathogens or their toxins pass through
the intestine and invade or affect other internal organs.
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C. Foodborne Toxicoinfections
 INTRODUCTION
 The
gastroenteritis caused by Clostridium perfringens,
Bacillus cereus, Vibrio cholerae, and enteropathogenic
Escherichia coli is described as toxicoinfection.
 The first two are Gram-positive sporeformers, and the
last two are Gram-negative small rods.
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... C. Foodborne Toxicoinfections
 The
following are some characteristics of foodborne
toxicoinfection:
1. For spore formers, ingestion of large numbers of live
vegetative cells is usually necessary.
2. Vegetative cells of spore formers do not multiply in the
digestive tract, but sporulate and release toxins.
3. For Gram-negative bacteria, live cells can be ingested in
moderate numbers.
4. Gram-negative cells rapidly multiply in the digestive tract.
5. Many cells also die, releasing toxins.
6. Toxins of both groups produce the gastroenteritis
symptoms.
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