Food poisoning caused by Gram positive microrganisms.

Food poisoning caused by Gram-positive microorganisms :

Various microorganisms cause the food poisoning such as Gram-positive microorganisms like Staphylococcus aureus and Bacillus cereus, which is also a spore-forming microorganism causes the severe type of food poisoning. These both microorganisms cause food poisoning mediated by exotoxin (enterotoxin is released).

Food poisoning caused by Staphylococcus aureus :

Staphylococcal food intoxication is one of the commonest types of food poisoning and is caused by the ingestion of enterotoxin formed in food during the growth of certain strains of Staphylococcus aureus . The enterotoxin produced by Staphylococcus aureus is termed as enterotoxin because it causes gastroenteritis i.e. inflammation of the epithelial lining of the intestinal tract.

Organism :

Staphylococcus aureus is the causative agent of Staphylococcal food intoxication. It is the small, Gram-positive microorganisms which are motile and non-spore formers. It has the spherical shape and typically occurs in grapes like cluster or in pear form or in the short chain.Most enterotoxin producingStaphylococcus aureus is coagulase positive and facultative anaerobes. Important characteristics of Staphylococcus aureus is the ability to tolerate high salt concentration as they can grow in media containing salt up to10-20% . They grow rapidly between the temperature range of 20-45*C.

Food involved:

The human carrier is mainly responsible for contamination of food with the enterotoxigenic strains of Staphylococcus aureus. These carriers harbour organisms in their nose, skin and mucous lining of their cells as normal flora and food may get contaminated during handling. For example, nasal secretion during sneezing is the main way of contamination in the food industry.Staphylococcus aureus growth is significantly reduced at the temperature below 4*C, Food kept in the refrigerator after preparation usually remains safe. However if not refrigerated and stored for the longer time, Staphylococci may multiply and produce enterotoxins. When this contaminated food is consumed may get food poisoning. Cooking does not necessarily destroy the toxin and enterotoxin are produced which are heat stable and can resist boiling for 30min or above. The food most commonly encountered are cream-filled baked food, meat and meat products, meat salad, eggs, etc.

Pathogenesis and disease:

Staphylococcus aureus produces seven different types of enterotoxins i.e. A, B, C₁, C₂, C_3, D and E. Among them, enterotoxin A which is a superantigen and is most frequently associated with Staphylococcal food intoxication. A superantigen functions by stimulating a large number of T- lymphocytes / T cells which in turn release cytokines. These cytokines activate a general inflammatory response in the intestine and results in gastroenteritis, including massive loss of fluid from the intestine.

The important characteristics of Enterotoxin are their stability towards heat. The condition most favour for toxin production is similar to the condition requiredStaphylococcus aureus for their growth. The toxin is produced at the temperature range of 15-46*C. The production of toxin is based at 40*C, the incubation period (time between consumption of food and appearance of first sign of symptoms.) The incubation period for Staphylococcal food poisoning is 2-4 hours. The duration of the infection is usually one or two days and is a self-limiting disease. The mortality rate is extremely low. The most common symptoms include:

• The patients may have nausea,retching(dry heaving), vomiting after production of enterotoxin.
• The patients may also have the abdominal cramp, loss of appetite, vomiting, mild fever, diarrhoea, etc.
• Blood and mucous may be present in stool and in vomitus in severe cases.
• Excessive loss of water from the body may cause dehydration.

Lab diagnosis:

The isolation of Staphylococcus aureus stool specimen (sample) may not be significant. General assay based on the selection ofStaphylococcus aureus in suspected food. To obtain quantitative data and to determine the extent bacterial contamination, the bacterial plate count is required. ForStaphylococcuscount is generally done in media containing the high concentration of salt.

Prevention and treatment:

A Staphylococcal food poisoning can be prevented by following methods :

• The good personal hygiene and proper sanitation in both preparation and production stage.
• Contamination of food can be reduced by heat treatment , by using the bacterial static agent and by changing pH (usually in acidic pH) of food.
• Mostly no treatment is given as it is a self-limiting disease and resolved within 24-48 hours.
• In severe cases, a saline situation may be given to restore electrolyte balance and to counter dehydration.
• Treatment with antidote may be useful.

Food poisoning caused by Bacillus cereus:

Bacillus cereus is becoming one of the most important causes of food poisoning. There are two types of Bacillus cereus food poisoning. The first type is caused by the Emetic toxin, resulting in vomiting, while the second type is caused by Enterotoxin which gives the diarrhoeal type of symptoms. In a small number of cases both types of symptoms are recorded, probably due to the production of both type of toxins.

Bacillus cereus

↓ (types of toxins)

1. Emetic toxin (Emesis -vomiting)
2. Enterotoxin (Diarrhoeal type disease)

• Enterotoxin T
• Three component Haemolysin (HBL)
• Non-haemolysin Enterotoxin (NHE)

Organism:

Bacillus cereus is Gram-positive, the spore-forming organism which is motile, aerobic as well as anaerobic and of rod shape.Bacillus cereus is not a competitive organism but grow well after cooking (less than 48*C) and cooling. The heat treatment will cause spore germination in the absence of competing for floral, vegetative cells ofBacillus cereus and grow well. The dominant type of disease caused byBacillus cereus differs from country to country. For example, in Japan, the emetic type is reported about ten times more frequently than diarrhoeal type, while in Europe and North America the diarrhoeal type is most frequently reported.

Food involved:

Bacillus cereus is a common soil saprophyte and is easily spread to many types of food especially of plant origins (fried and cooked rice, pasta, and noodles) but is also frequently isolated from meat and meat products, soup, milk and milk products.

Pathogenesis and disease:

The two types ofBacillus cereus of food poisoning caused by different types of toxin. The emetic toxin causing vomiting has recently been isolated and characterized while diarrhoeal type is caused by at least three different types of enterotoxin.

1. Emetic toxin: The emetic toxin causes emesis (vomiting ) only and is resistant to heat, pH, and proteolysis but not antigens. The biosynthesis of the emetic toxin still has to be elucidated (clarified). Although it has recently been reported that it stimulates vagus afferent through binding to the receptor. Vagus sensory neurons detect toxins that enter the gastrointestinal lumen and transmit information to the hindbrain, leading to nausea and vomiting.
2. Enterotoxin : There are three different types of enterotoxin produced byBacillus cereus which causes food poisoning i.e.

• Enterotoxin T
• Three component Haemolysin (HBL) which include 3 protein component i.e B. L₁ and L₂.
• Non-haemolysin Enterotoxin (NHE)

Characteristics of two types of disease caused byBacillus cereus :

Lab diagnosis:

Food poisoning caused by this organisms can be detected by the presence of toxin in the stool sample of infected individuals. The confirmatory test can be done with the isolation of causative agent from suspected food, coupled with symptoms.

Prevention and treatment:

The prevention can be done by:

1. Maintaining proper hygiene and sanitary condition farm to fork.
2. To prevent Bacillus cereus of food poisoning include eating food that has been canned properly with adequate heat treatment and adequate cooling.
3. Mostly no treatment is given as it is a self-limiting disease and resolved within 24-48 hours.
4. In severe cases, a saline situation may be given to restore electrolyte balance and to counter dehydration.
5. Treatment with antidote may be useful.

Reference:

1. Alexander, M. Introduction to Soil Microbiology. Academic Press, 1961.
2. Rangaswami, G and Bagyaraja PT. Agricultural Microbiology. 2nd. Prentice Hall of India, 1993.
3. RM, Atlas and R Bartha. Microbial Ecology : Fundamental and Applications. The Benjamin Cummins Publication Co. Inc., 1998.