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Food-Borne Infections and Intoxications
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Food infections are those in which
microorganisms present in the food at the time
of eating grow in the host and cause disease.
Food intoxications are those diseases in which
microorganism grow in the food, producing a
substance therein which is toxic to man and
animals.
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Food poisoning is the toxicity introduced into
food by microorganisms and their products.
This does not include the toxications which
follow the consumption of noxious plants
(mushrooms),poisonous fish (mussels), or
decomposed foods containing certain chemicals
(arsenic, lead, fluorides, antimony, mercury
salts).
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The term food infection is used to describe diseases
like salmonellosis and enteritis caused by
Salmonella spp and Cl. perfringens, since these
diseases are caused by the ingestion of organisms.
Food poisoning is an acute illness of sudden
onset caused by th consumption of
contaminated food or food which may contain
some form of poisonous agent.
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Intoxication
Infections
Staphylococcal ntoxication (
Salmonellosis - endotoxin of salmonella
staphylococcal enterotoxicosis) an spp.
enterotoxin produced by
staphylococcus aureus
Botulism - a neurotoxin produced Clostridium perfringens illness - an
by Clostridium botulinum
enterotoxin released during sporulation
of clostridium perfringens type A in the
intestinal tract
Bacillus cereus gastroenteritis - an
exoenterotoxin released during lysis of
Bacillus cereus in the intestinal tract
Enteropathogenic Escherichia coli
infection - several serotypes of E.coli
some invasive and some
enterotoxigenic
Yersiniosis,Shigellosis,Vibrio
parahaemolyticus infection etc..
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Groups of Food borne Pathogens
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Fecal-oral routes of transmission of food borne intestinal
pathogens. The direction is from bottom to top.
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Staphylococcal Poisoning
It is the most common type of food poisoning.
Certain strains of Staphylococcus aureus produce
a potent enterotoxin.
Ingestion of food containing this toxin causes a
sudden onset of illness within 3 to 4 hours.
Symptoms include nausea, vomitting and
diarrhoea.
Recovery is rapid, usually within 24 to 48 hours.
Death rarely occurs.
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Foods most commonly involved include those
which are eaten cold, e.g. salads, bakery products,
hams, pressed meat, and dairy products.
A food having millions of Staphylococci may taste,
smell, and appear to be little different from that
in which none of these organisms have grown.
Staphylococcal enterotoxin is heat resistant and
can withstand boiling for 30 minutes.
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Botulism
Botulism is caused by the exotoxin of Clostridium
botulinum, an anaerobic spore-forming rod.
Botulism is a neuroparalytic disease affecting
humans and animals.
Sixty to seventy percent of, cases are fatal.
The foods frequently implicated are those which
have been smoked, pickled, or canned, allowed to
stand for a time and then eaten without cooking
or with insufficient cooking.
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Bacterial Food Infections
Bacterial food infections include salmonellosis,
Clostridium perfringens gastroenteritis, Vibrio
parahaemolyticus infection .
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Salmonellosis
Salmonellosis is an infection resulting from ingestion
of the vegetative cells of Salmonella and is the
most frequently occurring bacterial food infection.
These bacteria grow well in the food at room
temperatures and have a pH range optimum for
growth between 4.1 to 9.0. Thus, they can also
grow in low acid foods.
Both animals and human beings are directly or
indirectly the sources of contamination of food with
Salmonella. The organisms may come from either
actual cases of disease or from the carriers. The
organisms may also come from cats, dogs, chickens,
cattle and other animals.
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The incubation period usually is between 4-36
hours .
Typical symptoms of Salmonella gastrointestinal
infections are nausea, vomitting, abdominal pain
and diarrhoea that usually appear suddenly and
which may be preceded by headache and chills.
Usually symptoms persist for 2-3 days. Salmonella
out breaks can be prevented by avoiding
consumption of contaminated food, destruction of
Salmonella by heat or by the prevention of
Salmonella growth by refrigeration or by other
means.
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Infection - Enteropathogenic E.coli
Causative Agent - Escherichia coli,strains both
invasive and enterotoxigenic.
Incubation Period and Symptoms - 8-24 hr,
invasive type and 8-44 hr enterotpxigenic type .
Foods Involved - Cheese, Milk,Foods etc.
Control Measures - Cook foods well in hygenic
conditions, use protected water,prevent food from
recontamination, use low temperature for storage,
reheat left overs
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Infection - Vibrio porahaemolyticus infection
Causative Agent - V.parahaemolyticus
Incubation Period and Symptoms - 2-48 hr
( generally 12 hr) abdominal pain, Diarrhoea,
Nausea, Vomiting, Mild Fever, Chills,Headache.
Foods Involved - Fish Foods
Control Measures - Cook foods well in hygenic
conditions, use protected water,prevent food from
recontamination, use low temperature for storage,
reheat left overs
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AEROMONAS SPECIES
Aeromonas species are gram-negative, non-sporeforming, bacteria, many of which are psychrotrophic
(i.e. able to grow at low temperatures).
Aeromonas species have been isolated from the
following food commodities: fresh vegetables; salads;
fish; seafood; raw meats including beef, lamb, pork
and poultry; and raw milk as well as high-pH cheeses
produced from raw milk.
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It is thought that when ingested, these organisms can
cause gastrointestinal disease in healthy individuals,
and septicaemia in the immunocompromised.
Sources
Aeromonas species are ubiquitous, although the
main source of the organisms is generally
accepted as water.
Measures to reduce the likelihood of high numbers
occurring should include: using treated water
supplies in food processing; keeping foods chilled;
and the thorough, frequent cleaning of equipment
used to process foods, especially those that are not
later cooked by the consumer, e.g. salads and
vegetables.
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BACILLUS SPECIES
The Bacillus genus is a group of gram-positive, sporeforming bacteria some of which, notably Bacillus
cereus and more rarely Bacillus licheniformis, Bacillus
subtilis and Bacillus pumilus, have been implicated in
foodborne disease.
Bacillus species are found in many raw and
unprocessed foods. However, B. cereus is commonly
associated with dried foods, spices, cereals
(particularly rice and pasta), as well as milk and
dairy products.
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Bacillus cereus food poisoning is caused by toxins
produced during the growth of the bacteria and
these toxins cause two distinctly different forms of
food poisoning.
Sources
Bacillus species are ubiquitous and are widespread in
the environment, being found in dust, soil, water, air
and vegetable matter.
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CAMPYLOBACTER
Campylobacter spp. are gram-negative, non-sporeforming bacteria, some of which (C. jejuni, C. coli, C.
lari and C. upsaliensis) are associated with
gastroenteritis.
Campylobacter is most often associated with fresh
poultry meat and related products.
Symptoms can vary widely and usually start with
muscle pain, headache and fever. Most cases
involve diarrhoea, and both blood and mucus may
be present in stools. Nausea occurs, but vomiting is
uncommon.
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Sources
Campylobacters are found in the intestinal tract of
many warm-blooded animals,such as cattle, sheep,
pigs, goats, dogs and cats, although they are especially
common in birds, including poultry. Wild birds are
thought to be a reservoir for domestic and food animals.
Consumer education and domestic hygiene training
can help prevent the transfer of Campylobacter from
raw to ready-to-eat foods. Consumers should be
advised not to wash meat and poultry carcasses prior
to cooking to help prevent water splashes and aerosols
from contaminating kitchen surfaces. Any surfaces
that could be potentially contaminated, such as in
meat-preparation areas, as well as chopping boards,
should be thoroughly disinfected after use.
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LISTERIA
The genus Listeria are gram-positive, non-sporeforming rod-shaped bacteria.
The genus contains a number of species including L.
monocytogenes, L. innocua, L. welshimeri, L.
seeligeri, L. ivanovii and L. grayi.
Listeria monocytogenes has the potential to be
present in all raw foods. Cooked foods can also be
contaminated, usually as the result of post-process
contamination.
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Listeria monocytogenes causes one of the most
severe forms of foodborne infection and it is
fortunate that listeriosis is a relatively rare disease.
The incubation period is 1 to 90 days (mean 30
days). The onset of illness is typically marked by flulike symptoms (fever and headache), and
sometimes by nausea, vomiting and diarrhoea.
In some cases these symptoms can lead on to
meningitis and septicaemia. Symptoms in pregnant
women can lead to infection of the foetus, which
can result in miscarriage, stillbirth, or the birth of an
infected infant, although the mother usually
survives.
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Sources
Listeria is ubiquitous in the environment. It is found
in soil, where it can survive for extended periods and
leads to the contamination of plant material.
The control of Listeria in foods relies largely on a
HACCP approach and the establishment of effective
critical control points in the process.
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SHIGELLA
Shigella species are gram-negative, non-spore-forming
bacteria belonging to the group Enterobacteriaceae.
Humans are the main reservoir for Shigella and
almost any food can become infected if it is
contaminated with faecal material from infected
individuals, or with sewage-contaminated water.
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The infective dose can be very low – as few as 10
cells can cause illness. The incubation time for illness
ranges from 12 h to 7 days (usually 1–3 days).
Shigell species can cause an asymptomatic infection,
mild diarrhoea, or can cause acute dysentery.
Typical symptoms are abdominal pain and cramps,
fatigue, fever and diarrhoea with mucus and
sometimes blood occurring in the faeces.
Frequent bowel movements can lead to
dehydration. Typically, symptoms last for between
3–14 days although longer-term complications such
as Reiter’s disease, reactive arthritis and haemolytic
uraemic syndrome can occur as a result of infection.
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Sources
Humans and higher primates are the main reservoir
for Shigella species. Individuals recovering from
infection can continue to shed the pathogen for
weeks after the symptoms have ceased and the
organism can survive for some time in faeces.
Measures to prevent food becoming contaminated
with Shigella spp should focus on preventing faecal
contamination of raw and processed foods and using
safe or treated water supplies for irrigation of crops
and for food processing.
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VIBRIO CHOLERAE
Vibrio cholerae is a gram-negative, non-sporeforming bacterium.
Vibrio cholerae can be present on food if it is
contaminated by polluted water, or by food handlers
carrying the pathogen. Contaminated water used to
make ice can lead to the contamination of beverages.
Typically, symptoms start with mild diarrhoea,
leading to more severe diarrhoea typified by the
production of grey ‘‘rice water’’ stools.
Nausea, abdominal pains and low blood pressure
can also occur. If untreated, the infection can lead to
dehydration, and in severe cases this can result in
death.
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Sources
Humans are the main reservoir for V. cholerae.
Individuals suffering from
cholera excrete large numbers of the organism into
the environment.
Measures to prevent food becoming contaminated
with V. cholerae should focus on preventing faecal
contamination of raw and processed foods and
using safe or treated water supplies for irrigation of
crops and for food processing.
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