Food Intoxication caused by Staphylococcus aureus

Food Intoxication caused by Staphylococcus aureus


  • 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.

About Organism

  • Typical growth of Staphylococcus is in masses that resemble clusters of grapes or in short chains or pairs.
Microscopic image of S. aureus
Microscopic image of S. aureus
  • 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.

About Enterotoxin

  • 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.

Food Involved:

  • 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:
    • Nausea
    • Vomiting
    • Diarrhea
    • Abdominal cramps
  • 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.

References and Sources


Also Read:

Leave a Comment

Exit mobile version