Foodborne illness is mostly related to gastrointestinal problems, it may involve microorganisms themselves or microbial products such as toxins.
The term food intoxication involves toxins produced by microorganisms in food substances and causes illness when it is consumed.
One of the most common food intoxications is caused by Staphylococcus aureus, which we are going to discuss here.
The key toxin of Staphylococcus intoxication is enterotoxin, which is produced during the growth of the microorganisms in the food.
Typical growth of Staphylococcus is in masses that resemble clusters of grapes or in short chains or pairs.
On media, it may appear yellow or golden or it might be unpigmented in some strains.
S.aureus producing enterotoxins are coagulase-positive ( which play a key role in coagulating blood plasma in staphylococcus infected patients) and also produce nuclease which is thermal-stable.
Facultative anaerobes in complex glucose medium, but usually grow better in aerobic conditions.
Some toxigenic S. aureus strains are salt-tolerant up to 10-20 % and also nitrites tolerant and also are dissolved sugar tolerant up to 50-60%.
They are proteolytic and fermentation in nature and don’t produce odors in foods.
Different six serological types are A, B, C1, C2, D & E that vary in toxicity, type A is a potent one mostly causing food poisoning.
Factors involved in Toxin Production by S. aureus in Foods
Different parameters are involved in toxin production such as type of food and its medium such as liquid or solid consistency, temperature, pH, and temperature.
Generally, the temperature range is about 4- 46 C, which actually depends on food , fo e.g., in condensed milk, custard , minimal temperature is 6.7-7.8 C, toxin production is slow at these temperatures range even can be extended at refrigeration storage period of time.
At aerobic conditions, growth is less as compared to anaerobic at minimal pH, for instance, minimal pH for aerobic condition is 4.8, and for anaerobic it is 5.5 pH.
Under aerobic & anaerobic conditions minimal water activity aw is 0.86 and 0.90.
Sources of Food poisoning Staphylococci
Nasal passage of humans have abundant amount of staphylococci present, which cause sinus infection.
Human Skin or animal sources.
Boils and wounds might be source of infection.
Staphylococcus produces enterotoxins in the food , which is a primary cause of food intoxication.
These are simple proteins with mol wt. between 26000- 30,000.
Cysteine loop is formed when single polypeptide chains are crossly linked through a disulfide bridge.
Mostly A and D types of enterotoxins are associated with outbreaks of food- poisoning.
The enterotoxins is produced only at abundant growth of Staphylococcus in food, for instance, population should be at least more than millions per ml or gram.
Best temperature of toxin production is 40 C , and range vary from 15.6 – 46.1C.
In suitable conditions, toxin production usually takes 4- 6 hrs.
Usually food contaminated after heat treatment is more likely to produce enterotoxins.
Food which contains proteins or starch enhance the production of toxin by staphylococcus for instance meat products and bakery products.
Enterotoxins are seen to be stable towards heat, mostly enterotoxin type B.
Various kinds of foods are involved, such as ham, poultry, bakery goods etc.
75% of staphylococcal food poisoning cases is caused by not sufficiently allowing food to cool.
The filling used in bakery goods are good source of microbial growth at room temperature.
Staphylococcus growth and toxin production mostly occurs in steam tables of cafeteria & restaurants or may be food vending which keeps the food heated for longer period of time.
Clinical Symptoms of Staphylococal Food Poisoning
Incubation period of Staphylococcus food intoxication, is short up to 2-4 hrs also may range between 1-7 hr.
Symptoms may vary in individual, in some people symptoms are minor , in others it can make them really ill.
Some common symptoms includes:
In severe cases, blood & mucus can be spotted in vomit and stools
It may also include sweating, chills, headache, weak pulse, and may be shallow respiration.
Mortality rate is low.
Treatment: In most cases no treatments is given, in severe cases, saline solutions is parenterally given to deal with dehydration.