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Food-Borne Infections and Intoxicat ions. Food infections are those in which microorganisms present in the food at the time of eating grow in the host and cause disease.
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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.
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).
The term food infection is used to describe diseases like salmonellosis and enteritis caused by Salmonella sppand 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.
Fecal-oral routes of transmission of food borne intestinal pathogens. The direction is from bottom to top.
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.
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.
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.
Bacterial Food Infections Bacterial food infections include salmonellosis, Clostridium perfringens gastroenteritis, Vibrio parahaemolyticus infection .
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.
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.
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
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
AEROMONAS SPECIES Aeromonas species are gram-negative, non-spore-forming, 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.
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.
BACILLUS SPECIES The Bacillus genus is a group of gram-positive, spore-forming 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.
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.
CAMPYLOBACTER Campylobacter spp. are gram-negative, non-spore-forming 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.
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.
LISTERIA The genus Listeria are gram-positive, non-spore-forming 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.
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 flu-like 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.
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.
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.
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.
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.
VIBRIO CHOLERAE Vibrio cholerae is a gram-negative, non-spore-forming 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.
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.
