Fish Microbiology and Quality Assurance

Unit 5 - Foodborne pathogens

5.3. Staphylococcus food intoxication
Staphalococcal food poisoning is caused by the ingestion of enterotoxin formed in food during growth of certain strains of Staphylococcus aureus. This bacterium produces an exotoxin called enterotoxin which causes gastroenteritis or inflammation of intestinal tract. S. aureus is a Gram positive cocci appearing as bunch of grapes.
Most of the entertoxin producing strains are coagulase positive (coagulate blood plasma), produce thermostable nuclease, facultatively anaerobic and grow better aerobically than anaerobic condition. However, some coagulase negative strain also produces entertoxin. These produce six neurologically distinct entertoxin (A, B, C, C2 D and E) which differ in toxicity. Most food poising involves types A or D. Grow in the temperature range of 4–40^oC with rapid growth taking placing in the temperature rage of 20-45^oC.

Source of staphylococcus to food
Source of staphylococci to foods are mainly from human and domestic animals (primary reservoirs). Commonly encountered in skin, hair, nasal passage, wound and throat. of humans. Food handlers are main source of food contamination with S. aureus. Besides, equipment and food contact surfaces also contribute for contaminatin with this organism.
Generally, conditions in foods that favour the growth of S. aureus (at about 40^oC) are more susceptible for food poisoning. Entertoxins are heat resistant and not inactivated at pasteurisation temperature. Normal cooking of food will not destroy toxin present in food. Seafoods support growth of S. aureus when contaminated. High salt tolerance and ability to grow at low water activity (0.86) helps this organism to have competitive advantage over other organisms especially in slat cured products such as smoked fish and salted fish.

Food involved in outbreaks
A variety of foods support the growth of S. aureus, and thus responsible for food poisoning outbreaks. The foods generally involved are Fish, meat, bakery products, salads etc.

Disease and symptoms
Individuals differ in their susceptibility to food poisoning and incubation period is more than 4 hrs. Symptoms of food poisoning is characterized by salivation, nausea, vomiting, abdominal cramps, diarrhoea, blood and mucus in stools, headache etc. Mortality is very low and infected persons recover except in extreme cases.

Condition necessary for outbreak

• Food must contain entertoxin producing staphylococci
• Food must support the growth and toxin production by staphylococci
• Temperature must be favorable for growth, and there should be enough time lapses since contamination for toxin production.
• Entertoxin bearing food must be ingested.

Prevention of food poising outbreaks

• Prevention of contamination of food with staphylococci
• Prevention of growth of staphylococci in foods.
• Avoiding consumption of contaminated food.