Bacterial Food
Infections
UNIT 11 BACTERIAL FOOD INFECTIONS
Structure
11.0 Objectives
11.1 Introduction
Zoonotic Diseases
11.2 Salmonellosis
11.3 Escherichia coli gastroenteritis
11.4 Bacillus cereus gastroenteritis
11.5 Cholera
11.6 Vibrio parahaemolyticus gastroenteritis
11.7 Shigella dysentery
11.8 Campylobacteriosis
11.9 Yersiniosis (Yersinia enterolytica infection)
11.10 Listeria monocytogenes infection (Listeriosis)
11.11 The Most Important Point to Remember to Wash you Hand
11.12 Let Us Sum Up
11.13 Key Words
11.14 Answers to Check Your Progress Exercises
11.15 Some Useful Books
11.0 OBJECTIVES
After reading this unit, you will be able to:
• describe major bacteria causes food born infections
• explain the mode of transmission of the food borne infection, symptoms
and preventive measures.
11.1 INTRODUCTION
Food infection occurs when a pathogen enters the gastrointestinal tract and
multiplies. Microorganisms can penetrate into the intestinal mucosa and grow
there, or they can pass through other systemic organs. Infections are
characterized by a delay in the appearance of gastrointestinal disturbance while
the pathogen increases in numbers or affects invaded tissue. There is also
usually a fever, one of the body’s general responses to an infective organism.
Foodborne infections remain a major public health problem. The Council for
Agricultural Science and Technology estimated in its 1994 report, Foodborne
Pathogens: Risks and Consequences, that as many as 9,000 deaths and 6.5 to
33 million illnesses in the United States each year are food-related.
11.1.1 Zoonotic Diseases
The World Health Organization defines Zoonoses (Zoonosis, sing.) as "Those
diseases and infections which are naturally transmitted between vertebrate
animals and man".
Mode of transmission: Feces, urine, saliva, blood, milk, via aerosol, oral,
contact with bedding or animals, etc.
39
, Food Poisoning
Approximately 150 zoonotic diseases are known to exist. Wildlife serves as a
reservoir for many diseases common to domestic animals and humans. Persons
working with wildlife should be alert to the potential for disease transmission
from animals. Generally, disease is more easily prevented than treated. Many
zoonotic diseases are so common in nature, so rare in humans, or so mild in
their symptoms, that wild animals pose a minimal health risk to people.
Zoonotic diseases include:
• Those which can be transmitted directly from animals to humans (e.g.
rabies).
• Diseases that can be acquired indirectly by humans through ingestion,
inhalation or contact with infected animal products, soil, water, or other
environmental surfaces which have been contaminated with animal waste
or a dead animal (e.g. salmonellosis, leptospirosis, anthrax). Campylobacter
infection is mainly found in chicken meat. Listeriosis and E.coli
gastroenteritis are two other common infections caused by zoonotic agents.
All these will be discussed one by one.
• A disease which has an animal reservoir, but requires a mosquito or other
arthropod to transmit the disease to humans (e.g. St. Louis encephalitis,
Rocky Mountain spotted fever).
11.2 SALMONELLOSIS
Salmonellosis is the most reported zoonotic disease in European countries.
Salmonellosis (Salmonella gastroenteritis) results from the ingestion of foods
that contain significant numbers of viable cells of the members of the genus
Salmonella. It is the most frequently occurring food borne infection.
Salmonella are small gram negative, motile, non-spore forming rods that
ferment glucose, usually with gas, but usually do not ferment lactose or
sucrose. They are widely distributed in nature, with humans and animals being
their primary reservoir. Generally large number of salmonellae typically 106 to
109 bacterium must be ingested to cause illness.
Occurrence: The initial source of the bacteria is the intestinal tract of animals
such as birds, reptiles, farm animals, humans and occasionally insects. As
intestinal form, the organisms are excreted in feces from which they maybe
transmitted by insects and other living creatures to a large number of places,
polluted water and contaminated food. The organism may get transferred from
actual infected cases of the disease or from carriers. A carrier is defined as a
person or an animal that repeatedly sheds bacteria, usually through feces,
without showing any signs or symptoms of the disease. Infected rodents, rats
and mice may contaminate unprotected foods with their feces and thus spread
Salmonella bacteria. Flies may play an important role in the spread of
Salmonella, especially from contaminated fecal matter to foods. Humans
acquire the bacteria from contaminated food such as beef products, poultry,
eggs, egg products or water.
Symptoms: The susceptibility of humans varies with the species and strains of
the organism and the total number of bacteria ingested. A longer incubation
period usually distinguishes salmonellosis from staphylococcus poisoning:
40usually 12-36 hours for the former and about 2-4 hours for the latter. The
Infections
UNIT 11 BACTERIAL FOOD INFECTIONS
Structure
11.0 Objectives
11.1 Introduction
Zoonotic Diseases
11.2 Salmonellosis
11.3 Escherichia coli gastroenteritis
11.4 Bacillus cereus gastroenteritis
11.5 Cholera
11.6 Vibrio parahaemolyticus gastroenteritis
11.7 Shigella dysentery
11.8 Campylobacteriosis
11.9 Yersiniosis (Yersinia enterolytica infection)
11.10 Listeria monocytogenes infection (Listeriosis)
11.11 The Most Important Point to Remember to Wash you Hand
11.12 Let Us Sum Up
11.13 Key Words
11.14 Answers to Check Your Progress Exercises
11.15 Some Useful Books
11.0 OBJECTIVES
After reading this unit, you will be able to:
• describe major bacteria causes food born infections
• explain the mode of transmission of the food borne infection, symptoms
and preventive measures.
11.1 INTRODUCTION
Food infection occurs when a pathogen enters the gastrointestinal tract and
multiplies. Microorganisms can penetrate into the intestinal mucosa and grow
there, or they can pass through other systemic organs. Infections are
characterized by a delay in the appearance of gastrointestinal disturbance while
the pathogen increases in numbers or affects invaded tissue. There is also
usually a fever, one of the body’s general responses to an infective organism.
Foodborne infections remain a major public health problem. The Council for
Agricultural Science and Technology estimated in its 1994 report, Foodborne
Pathogens: Risks and Consequences, that as many as 9,000 deaths and 6.5 to
33 million illnesses in the United States each year are food-related.
11.1.1 Zoonotic Diseases
The World Health Organization defines Zoonoses (Zoonosis, sing.) as "Those
diseases and infections which are naturally transmitted between vertebrate
animals and man".
Mode of transmission: Feces, urine, saliva, blood, milk, via aerosol, oral,
contact with bedding or animals, etc.
39
, Food Poisoning
Approximately 150 zoonotic diseases are known to exist. Wildlife serves as a
reservoir for many diseases common to domestic animals and humans. Persons
working with wildlife should be alert to the potential for disease transmission
from animals. Generally, disease is more easily prevented than treated. Many
zoonotic diseases are so common in nature, so rare in humans, or so mild in
their symptoms, that wild animals pose a minimal health risk to people.
Zoonotic diseases include:
• Those which can be transmitted directly from animals to humans (e.g.
rabies).
• Diseases that can be acquired indirectly by humans through ingestion,
inhalation or contact with infected animal products, soil, water, or other
environmental surfaces which have been contaminated with animal waste
or a dead animal (e.g. salmonellosis, leptospirosis, anthrax). Campylobacter
infection is mainly found in chicken meat. Listeriosis and E.coli
gastroenteritis are two other common infections caused by zoonotic agents.
All these will be discussed one by one.
• A disease which has an animal reservoir, but requires a mosquito or other
arthropod to transmit the disease to humans (e.g. St. Louis encephalitis,
Rocky Mountain spotted fever).
11.2 SALMONELLOSIS
Salmonellosis is the most reported zoonotic disease in European countries.
Salmonellosis (Salmonella gastroenteritis) results from the ingestion of foods
that contain significant numbers of viable cells of the members of the genus
Salmonella. It is the most frequently occurring food borne infection.
Salmonella are small gram negative, motile, non-spore forming rods that
ferment glucose, usually with gas, but usually do not ferment lactose or
sucrose. They are widely distributed in nature, with humans and animals being
their primary reservoir. Generally large number of salmonellae typically 106 to
109 bacterium must be ingested to cause illness.
Occurrence: The initial source of the bacteria is the intestinal tract of animals
such as birds, reptiles, farm animals, humans and occasionally insects. As
intestinal form, the organisms are excreted in feces from which they maybe
transmitted by insects and other living creatures to a large number of places,
polluted water and contaminated food. The organism may get transferred from
actual infected cases of the disease or from carriers. A carrier is defined as a
person or an animal that repeatedly sheds bacteria, usually through feces,
without showing any signs or symptoms of the disease. Infected rodents, rats
and mice may contaminate unprotected foods with their feces and thus spread
Salmonella bacteria. Flies may play an important role in the spread of
Salmonella, especially from contaminated fecal matter to foods. Humans
acquire the bacteria from contaminated food such as beef products, poultry,
eggs, egg products or water.
Symptoms: The susceptibility of humans varies with the species and strains of
the organism and the total number of bacteria ingested. A longer incubation
period usually distinguishes salmonellosis from staphylococcus poisoning:
40usually 12-36 hours for the former and about 2-4 hours for the latter. The
