CAUSATIVE ORGANISMS OF FOOD-BORNE

Clostridium perfringens Vibro parahaemolyticus Clostridium butulinum Outline Salmonella Clostridium perfringens Staphylococus aureus Vibro parahaemolyticus Bacillus cereus Clostridium butulinum Escherichia coli Shigella Vibro chorelae

Salmonella Salmonella are Gram negative, motile rods with a facultative anaerobic type metabolism. Salmonella typhi and S. paratyphi cause the typhoid fevers. The disease has a mortality rate of around 10%. Salmonella typhimurium, S. agona, S. panama are just a few of the many species which cause classical gastroenteritis type food poisoning. Mortality rates are less than 1% but increase with young, old or infirmed people.

Salmonella food poisoning is mainly associated with freshly cooked meat and poultry products which have in some way been undercooked and mishandled before consumption. The cycle of Salmonella food poisoning transmission may be summarised as follows: A knowledge of this cycle is important in controlling spread of Salmonella food poisoning.

Clostridium perfringens Clostridium perfringens is a Gram positive, spore forming, rod shaped bacterium which is non-motile and anaerobic. Clostridium perfringens multiplies very rapidly in the temperature range 37O- 55OC with a cell division occuring every 10-15 minutes. .The presence of this organism in a product is often considered as an index of faecal pollution. Meat and poultry products are frequently contaminated with this organism.

Staphylococcus aureus Cells of Staphylococcus aureus are Gram positive cocci which are generally arranged in grape like clusters. They are non-motile, facultative anaerobes and may grow in products containing up to 16% NaCl. Staphylococcus aureus food poisoning is mostly associated with cooked food products - in particular those which have been subject to human handling such as cooked meats and chicken, cooked peeled prawns, hams, bacon, lunch meats, and dairy products such as cream cakes, custard pies and cheeses.

Vibrio parahaemolyticus These are small Gram negative, motile rods, which are facultatively anaerobic. They have an obligate requirement for salt and are essentially marine in habitat Symptoms of Vibrio parahaemolyticus food poisoning develop around 12-30 hours after consumption and include diarrhea, vomiting and fever. Symptoms last 2-5 days and the infective dose is around 106 cells.

Bacillus cereus These are Gram rods, motile, and which form spores. They are faciltative anaerobes and occur widely in soils and waters. Surveys in the incidence of this organism in foods show a high frequency of insidence in dried foods such as cereals, spices and powdered milk.

Clostridium botulinum Clostridium botulinum is a Gram positive, anaerobic, spore forming rod. It occurs in soils, waters and marine sediments and may combinate a wide variety of products such as fruits, vegetables, meats and seafoods. Clostridium botulinum food poisoning (botulism) is largely associated with processed foods, in paricular heat processed foods, where processing has failed to eliminate the spores of the organism.

Escherichia coli Escherichia coli is a normal inhabitant of the intestinal flora of man and animals. It is a Gram negativee, motile, facultatively anaerobic rod and belongs to the family Enterobacteriaceae. The organism enters kitchen and food preparation areas in many raw foodstuffs and readily passes to cooked foods by the usual means of hands, surfaces, containers, and other equipment. The incubation period is 1-3 days and the symptoms may resemble those of Salmonella food poisoning or dysentery.

Shigella Shigella belongs to the family Enterobacteriaceae. There are four species Sh. sonnei , Sh. boydii, Sh. flexneri and Sh. dysenteriae and the cells are Gram negative, non-motile, facultatively anaerobic rods. The shigellae produce an acute intestinal infection characterized by diarrhea associated with fever and vomiting. The incubation period ranges from 1-7 days.

Vibrio cholerae Vibrio cholerae is a Gram negative, polarly flagellated aerobic rod. It has simple nutritional requirements and is quite insensitive to alkaline conditions, being able to grow at pH 9.0-9.6. Vibrio cholerae is an intestinal pathogen causing cholera which is chacarterized by a sudden onset of profuse, watery diarrhea and vomiting.