Download Food Infections and Poisoning -UNIT-2-2012

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Bacterial Food Borne Diseases
To control and prevent the development of food poisoning and to prevent the spread of disease by foods is an
important aspect of food microbiology. All food borne diseases are classified as food infections or food
intoxications. These classifications are somewhat arbitary.
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. 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). At one time it was believed that the products of putrefaction were the cause of food poisoning. These were
called ptomaines, and were produced in putrefied meat and other proteinaceous foods.
These are amines and result chiefly from the decarboxylation of amino acids. It could be demonstrated that
ptomaines injected into animals were toxic, but when taken experimentally by mouth, they were not especially
toxic. The food poisoning, therefore, could not be due to ptomaines.
People generally do not eat foods that show visible spoilage, but sometimes if the appearance, flavour, and taste is
normal, they do eat them. On the other hand, certain foods may show no signs of spoilage and yet be responsible
for food poisoning.
The fact that organisms are present in food does not necessarily mean that they are harmful.
Most of the organisms that cause spoilage of foods are harmless saprophytes. However, there are some forms of
illness caused by organisms growing in foods. Staphylococcal food poisoning and botulism are defined as food
intoxications, since injestion of the toxin causes the disease symptoms.
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 injestion of organisms.
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Bacterial Food Borne Diseases
Intoxication
Infections
Staphylococcal ntoxication (
staphylococcal enterotoxicosis) an
enterotoxin produced by staphylococcus
aureus
Salmonellosis - endotoxin of salmonella spp.
Botulism - a neurotoxin produced by
Clostridium botulinum
Clostridium perfringens illness - an 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..
Staphylococcal Poisoning - It is the most common type of food poisoning. Certain strains of Staphylococcus
aureus produce a potent enterotoxin. Injestion 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.
The organisms are widely distributed upon the skin and mucous membranes of the human body. People who
handle foods contaminate them ignorantly of carelessly. 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. Secondly, staphylococcal enterotoxin is heat resistant and can withstand boiling
for 30 minutes.
So recooking the food does not help. Control is by preventing the entry of the bacteria to food, by destruction of
the bacteria by heat, and by restriction of their growth by refrigeration.
Botulism - Botulism is caused by the exotoxin of Clostridium botulinum, an anaerobic spore-forming rod. It is
one of the most potent exotoxins known to man. Botulism is a neuroparalylic disease affecting humans and
animals. Sixty to seventy percent of, cases are fatal. The foods frequently implicated are those which have been
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smoked, pickled, or canned, allowed to stand for a time and then eaten without cooking or with insufficient
cooking.
This means that the preservative treatment is inadequate and has failed to destroy the spores of Clostridium
botulinum. Most cases are associated with home canned vegetables, infected sausages, ham, preserved meats
fowl, or fish.
These foods have the common property of being high in protein, near neutral in pH, and have little residual
available oxygen, all of which are factors contributing to toxin production. Fortunately, the toxin is heat labile and
is destroyed very quickly by boiling. Home canned food should always be heated at the boiling point for several
minutes before use.
Bacterial Food Infections - Bacterial food infections include salmonellosis, Clostridium perfringens
gastroenteritis, Vibrio parahaemolyticus infection etc.
1) Salmonellosis is an infection resulting from ingestion of the vegetative cells of Salmonella and is the most
frequently occurring bacterial food infection. Salmonella infection can be caused by a large number of species
and serotypes of Salmonella. 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.
The lowest aw for growth varies with the food but varies from 0.93 to 0.95. These organisms can attain
considerable numbers causing detectable changes in appearance, odour or taste of foods in which they grow.
Infection follows consumption of the food.
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.
Individuals differ in their sensitivity to Salmonella infection but in general, morbidity is high in any outbreak.
Susceptibility varies with the species, strains and the total number of bacteria ingested. The incubation period
usually is between 4-36 hours compared to 2-6 hours in the case of staphylococcal poisoning. 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. Mortality is low and the severity and the duration
varies with the number of bacteria ingested. 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.
2) E. coli is generally regarded as a part of the natural flora of the human and animal intestinal tract. However, in
recent years, several serotypes of E. coli have been implicated in human and animal diarrhoeal diseases. The
organisms responsible for such food poisoning outbreaks have been designated as enteropathogenic E. coli (EEC)
. Some of these EEC produce an enterotoxin which causes cholera like or enterotoxigenic illness in humans. This
can be serious specially in children. Following ingestin of these organisms, the bacteria colonize the upper
intestine and produce an enterotoxin which apparently mediates the movement of water in the intestinal lumen.
Such fluid accumulation occurs in the absence of invasive bacteria.Groups of E. coli that cause colitis (dysentry
like syndrome) are nonenterotoxigenio but penetrate the epithelial cells of the colonic mucosa. For either the
enterotoxigenic or the invasive illness to occur a large dose of the EEC is required. Therefore, foods which are
highly contaminated or inadequately preserved allow the growth of these organisms. These organisms al e
relatively heat sensitive and can be readily destroyed by pasteurization or by proper cooking methods.
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3) Vibrio parahaemolyticus gastroenteritis is also a commonly occurring food intoxication. This organism
which is a Gram-negative, curved rod shaped and motile will grow at seven per cent salt concentration with an
optimum temperature of 35-37°C. This has been isolated from many sea foods but can be killed by proper
cooking.
Other organisms implicated in food borne disease outbreaks are species of Yersinia, Arizona, Streptococcus
pyogenes and S. faecalis. The food infections caused by these result from the growth and increase in the dosage of
the pathogen. Some of these organisms can tolerate a salt concentration of 5-6 per cent. However, no enterotoxin
production by these organisms has been so far demonstrated.
4) Clostridium perfringens and Bacillus cereus.:Among the spore forming bacteria that cause food infections
are the Clostridium perfringens and Bacillus cereus. Clostridium perfringens gastroenteritis is caused by C.
perfringens (welchii) which is a Gram positive, anaerobic, nonmotile spore former with an are optimal growth
temperature of 37-43°C. Spores of this organism are heat resistant and are' found in raw food, soil, sewage and
animal faeces. Most commonly, meat that has been cooked and allowed to cool slowly before consumption
permits the growth of these organisms. Cooking destroys only the vegetative cells and during cooling,
germination and growth of spores occurs, if the food is not adequately refrigerated.
Symptoms of the disease which appear following ingestion of the food in 8-24 hours are acute abdominal pain
and diarrhoea. Fever and nausea are rare. Ingestion of millions of viable cells ore required for symptoms to
appear. The enterotoxin is released in the gut during sporulation and results in excessive fluid accumulation in the
intestinal lumen. The enterotoxin is relatively heat sensitive and is inactivated at 60°C for 10 minutes. Prevention
of outbreaks includes rapid cooling of cooked meats and other foods and reheating of left overs before
consumption.
Bacillus cereus which is a Gram positive, aerobic spore forming rod-shaped organism has been reported as an
etiologic agent in numerous food poisoning outbreaks. The spores are heat resistant and survive considerable
degree of cooking. For symptoms to develop, large number of cells have to be ingested. The mechanism of
pathogenicity is believed to involve lysis of the bacterial cells in the intestinal tract and the release of enterotoxin
which appears to be a protein.
Bacterial Food Borne Infections
Infection - Salmonellosis
Causative Agent - Salmonella enteritidis serotypes
Incubation Period and Symptoms - 5-72 hours ( usually 12-36 hr)
diarrhoea,Vomiting,Dehydration,Headache,Duration several days
Foods Involved - Cooked Foods
Control Measures - Cook foods well in hygenic conditions, use protected water,prevent food from
recontamination, use low temperature for storage, reheat left overs
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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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
Food Poisoning
1) Staphylococcal Poisoning - It is the most common type of food poisoning. Certain strains of Staphylococcus
aureus produce a potent enterotoxin. Injestion 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.
The organisms are widely distributed upon the skin and mucous membranes of the human body. People who
handle foods contaminate them ignorantly of carelessly. 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. Secondly, staphylococcal enterotoxin is heat resistant and can withstand boiling
for 30 minutes.
So recooking the food does not help. Control is by preventing the entry of the bacteria to food, by destruction of
the bacteria by heat, and by restriction of their growth by refrigeration.
2) Botulism - Botulism is caused by the exotoxin of Clostridium botulinum, an anaerobic spore-forming rod. It is
one of the most potent exotoxins known to man. Botulism is a neuroparalylic 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.
This means that the preservative treatment is inadequate and has failed to destroy the spores of Clostridium
botulinum. Most cases are associated with home canned vegetables, infected sausages, ham, preserved meats
fowl, or fish.
These foods have the common property of being high in protein, near neutral in pH, and have little residual
available oxygen, all of which are factors contributing to toxin production. Fortunately, the toxin is heat labile and
is destroyed very quickly by boiling. Home canned food should always be heated at the boiling point for several
minutes before use.
3) Perfringens Poisoning - Another type of food poisoning is caused by strains of Clostridium perfringens
(formerly called Cl. welchii). Although this organism forms toxin during its growth, a filtrate of the growth
medium does not induce the poisoning. The development of food poisoning symptoms requires the growth of
organisms in the human intestine.
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Growth is very rapid and causes mild illness, with diarrhoea and abdominal pain, but rarely vomitting. The onset
of symptoms occurs between 8 to 22 hours after the food has been eaten. The organism is more important as a
cause of gas gangrene, which consistently involves the muscles. Perfringens poisoning has been caused by the
injestion of prepared meats or meat products and poultry.
These foods arc cooked, allowed to cool slowly, left overnight at room temperature, and eaten the next day. What
probably happens is that spores of the organisms survive the heating applied during cooking, and germinate into
vegetative cells when the food is kept at a temperature suitable for growth. The vegetative cells multiply and grow
to numbers which are infective.
4) Streptococcal Poisoning - It has been reported that food which appeared to be the cause of gastroenteritis in
humans contained large numbers of Streptococcus faecalis. These organisms are referred to as enterococci
because they are frequently found in the human intestinal tract. Poisoning is caused by inadequately refrigerated
food contaminated with organisms.
Food Borne Fungal Intoxications - Mycotoxins -Mycotoxins are fungal metabolites elaborated by fungi and
which are effective against both animals and birds. A variety of fungi are known to produce mycotoxins and these
include aspergilli, penicilli, Rhizopus and fusana. It now appears that most fungi have the potential to produce a
toxin under one set of conditions or the other. The syndrome that results from the ingestion of the toxin
containing food is referred to as mycotoxicosis.
The first documented case of mycotoxicosis is attributed to the consumption of food infected with the rye ergot
(Claviceps purpurea). Subsequently, several descriptions of mold poisoning such as the Aspergillus toxicity in
cattle in 1924, stachybotrytic toxicosis in 1931and moldy corn poisoning in 1940 have appeared. The Turkey 'X'
disease was first repotted in 1960 and Aspergillus fiavus was identified as the fungus producing aflatoxin. Since
then, aflatoxins have been recognized both as potential toxins as well as carcinogens and a major threat to public
health.
Mycotoxins - Mycotoxins are chemical substances produced by a variety of moulds in staple foods such as corn,
wheat, rice, and peanuts. These toxins produce illness or death in small animals and in many cases arc
carcinogenic. Aspergillus produced by Aspergillus fiavus and by some other moulds are now known to be health
hazards, not only for animals but for humans too.
Besides aflatoxins, various other mycotoxins arc also produced by certain moulds. These mycotoxins are
produced on rye or rye bread, corn, and other grains by Claviceps purpuria, Penicillium rubrum, Fusarium
sporotrichiella and other fungi.
Aflatoxins and Related Compounds
- Moldy feed toxicosis was recognized as a serious livestock problem in the 1950's but it was only in 1960 during
the investigations in the United Kingdom of moldy feed toxicosis which was called "Turkey X disease", that A.
flavus and A. parasiticus were identified as the organisms responsible for the elaboration of the toxin in the feed.
The earliest symptoms of the disease are lithargy and muscular weakness followed by death. The term aflatoxin
now refers to group of bisfuranocoumarin metabolites isolated from strains of A. flavus group of fungi.
These aflatoxins flurosece strongly in ultra violet light. The major members are designated as B1, B2, GI and G2.
B1 and B2 fluoresce blue, while Gl and G2 fluoresce green. In some animal species such as in dairy cattle,
aflatoxin B1 and B2 are partially metabolized to the hydroxylated derivates namely M I and M2, respectively.
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Aflatoxin PI is a urinary l11etabolite of Bl in monkeys. The structure of the four aflatoxins and lists the details of
these toxins
All aflatoxins absorb UV light in the range of 362-363 nm, a characteristic used in preliminary identification. The
growth of toxigenic molds and elaboration of the toxin Occurs if moisture conditions are ideal following harvest
and storage.
Although initially aflatoxin was detected in the peanut meal it is now known that a variety of cereals, and other
plant products are susceptible to fungal invasion and mycotoxin production. Because of the wide spread nature of
fungi producing aflatoxins in food materials, it has become almost impossible to lay down standards. As a result,
international agencies have now permitted the presence of 20 ppb of aflatoxin in food materials as the maximum
permissible level.
A large number of fungi are today known to produce different toxins and some of these are Patulin, Ochratoxin,
Sterigmatocystin, Penicillic acid etc. Patulin was first isolated in 1942 and described as an antibiotic but later
classified as a mycotoxin.
Today, several molds including aspergilli and penicilli. have been reported to produce this toxin which is
effective against bacteria such as E. coli and stapbylococci. It is also fungistatic and is toxic to seed and seedlings
of higher plants.
Oral and intravenous injection of patulin are fatal (0.3-2.4 mg/g of body weight) to mice and rats. Pathological
changes include brain edema, lung haemorrhage and capillary damage in the liver and kidneys. This toxin has
also been found to be a potenital carcinogen. Patulin has been detected in apple juice and cider, prepared from
apples infected with patulin producing strains of Penicillium expansum. Ochratoxin is another fungal metabolite
first isolated from the culture filtrates of Aspergillus ochraceus. Several types are known which differ in the type
of fluorescence. These are toxic to ducklings, chicks and rats and are heat resistant.
Citrinin was first isolated in 1937 from Penicillium citrinum as an antibiotic but later found to be a toxin. Many
species of Penicillium, Aspergillus terreus and Aspergillus niveus are now known to produce this mycotoxin.
Several fungi are known to produce toxins which cause sustained tremors, convulsion and death and these are
collectively called as tremorogenic mycotoxins. None of these have been found as naturally occurring
contaminants in feed material. However, toxigenic isolates have been obtained from conventional cattle feed,
peanuts, etc.
Species of Fusarium are widespread in nature. Mostly saprophytes although some cause plant diseases. In recent
years, these organisms have also been implicated in mycotoxicosis. Barley infected with F. saubinette has been
found to be toxic to swine. Several species of Fusarium are known to produce more than one type of toxin when
colonizing plants or cereal grains. These toxins include Zearalenone, a variety of Trichothecenes group of toxins.
These cause a hyperestrogenic syndrome, haemorrhage and in some cases even abortion in swine.
The list of mycotoxins is far from complete and the number of fungi producing toxins is steadily increasing. Some
of these metabolites may also be carcinogenic. The wide range of effects of different toxic metabolite has made
the establishment of a safe level in human foods difficult.
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Physical and Chemical Properties Some Aflatoxins and Derivatives
Fluorescence
Aflatoxin Molecular Formula Molecular Weight Melting Point emission at
(nm)
B1
C17H12O6
312
268-269
425
B2
C17H14O7
314
286-289
425
G1
C17H12O6
328
244-246
450
G2
C17H12O6
330
237-240
450
M1
C17H12O6
328
299
425
M2
C17H14O7
330
293
-
P1
C16H10O6
298
320
-
Viruses in Food
Several viruses are known to be carried through food and water and cause infection in humans and animals.
Poliomyelitis for example is known to be a food borne viral infection carried through milk.
The hepatitis virus (causing jauntice) is another virus that is transmitted through the oral route as a result of
consuming age contaminated water and sea foods. The onset of symptoms occurs long time after intake.
Some viruses are also known to survive low temperature storage although resistance to heat and resistance during
storage varies considerably among these viruses. Those resistant to cold storage can cause problems when food
stored is used without proper processing.
Algal Poisoning - Fish or shellfish such as scallops, clams, mussels, etc. consume algae, namely, Gymnodinium,
Gonyaulax and others. These algae are toxic and - may lead to fish poisoning in humans. Commercially harvested
shell fish are now routinely assayed for the presence of toxins.
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