Food poisoning is an everyday problem and often times it is related to the food that we eat. The debate on food poisoning and its association with Bacillus cereus is not new. But not many people know about it. Only if the working of this bacterium Bacillus cereus is clear, it is easy to guess how Bacillus cereus is associated with food poisoning.
What is Bacillus cereus?
Bacillus cereus is a Gram-positive, spore-forming and toxin-producing bacterium. Bacillus cereus can grow aerobically and anaerobically as well.
It is one of the most common causes of food poisoning in the industrialized world. The food poisoning caused by this bacterium is also known as “Fried Rice Syndrome”.
The food poisoning caused by Bacillus cereus is of two different types which are followings:
- The diarrhoeal type
- The emetic type
In the diarrhoeal type of food poisoning is caused by complex enterotoxins. These complex enterotoxins are produced during the vegetative growth of Bacillus Cereus in the small intestine.
In the emetic type of food poisoning, the emetic toxin is produced by the growing cells of Bacillus Cereus in the food.
In both the types of food poisoning, the food involved has already been heated, and the surviving spores are the cause of food poisoning.
The heat treatment induces spore germination, and B. cereus grows in the absence of other competing flora.
Toxins Produced by Bacillus Cereus
Bacillus Cereus produces two types of toxins which are:
- Emetic toxin
One emetic toxin is produced by Bacillus Cereus. It is a ring-shaped structure and is made up of three repeats of four amino or oxyacids. The molecular mass of the ring structure is 1.2 kDa. The emetic toxin is chemically related to the potassium ionophore valinomycin. The emetic toxin causes emesis (vomiting) only. The emetic toxin is also named as named “cereulide”. The emetic toxin is resistant to proteolysis, heat, and ph.
Total of three enterotoxins is produced by Bacillus Cereus. Two out of three are found to be involved in food poisoning. Both toxins contain three different proteins that act together to cause poisoning.
The third enterotoxin is a haemolysin. This haemolytic enterotoxin is not known to be involved in food poisoning.
The experiments show that, in body, the enterotoxins are degraded on its way to the ileum. The enterotoxin can be performed, and the number of B. cereus cells in the food would be higher. This higher number is enough to cause food poisoning and such products should not be consumed.
Bacillus Cereus Outbreaks
Studies suggest that 63,000 cases of food poisoning are caused by Bacillus Cereus each year in the United States.
However, many cases are unreported. The type of disease caused by B. cereus differs from country to country. In Japan, the emetic type of food poisoning is reported 10 times more than the cases of diarrhoeal type food poisoning.
In North America and Europe, the diarrhoeal type of food poisoning is reported more frequently than others.
Bacillus Cereus was considered the cause of 33% in Norway, 22% in Finland, 47% in Iceland, 8.5% in the Netherlands, and 5% in Denmark.
The Bacillus cereus bacterium produces two types of toxins. One of the toxins causes diarrhea while the other toxin causes vomiting.
When the bacteria are ingested, the one type of toxin is released within the small intestine. The release of these toxins causes cramps, diarrhea, and nausea. It rarely causes vomiting. The symptoms usually begin six to fifteen hours after the consumption of contaminated foods. The foods contaminated with it can include meat, milk, vegetables or fish.
The second type of toxin is released by the Bacillus Cereus bacterium into the food before its consumption. This toxin can cause nausea and vomiting within the thirty minutes to six hours after the consumption of food. starchy foods, like rice, are most commonly affected by these toxins.
Diagnosis, Treatment, and Complications
Bacillus Cereus food poisoning can be diagnosed by testing and analyzing the patient’s vomit or feces. The presence of bacterium is an indication of bacterium-induced food illness. various culture media are available to culture this pathogen. Commercial kits are also available for the detection of diarrhoeal enterotoxin but are not available for the emetic toxin.
Bacillus cereus food poisoning can be treated easily. In most cases, rest and keeping the body well-hydrated is helpful. It allows the body to rid of infection-causing bacteria typically within a day.
If the condition requires medical treatment, then the doctors focus on the treatment of symptoms.
The main treatment for this purpose is the administration of intravenous fluids for dehydration. Antibiotics such as vancomycin can also be prescribed for serious conditions (prolong condition)
Some cases complications can also occur in people with compromised immune systems or those having surgical wounds or people using intravenous drugs.
Complications related to Bacillus Cereus food poisoning are aseptic meningitis, gangrene, and cellulitis.
Bacillus Cereus is present everywhere in the environment, therefore control measures should be taken to prevent the growth of Bacillus Cereus and the formation of emetic toxin in the food. Following measures can be taken to prevent the chances of illness associated with it:
- The scientific studies explain that keeping the cold foods cold (lower than 4 C, or 40 F) and hot foods hot (above 60 degrees Celsius, or 140 degrees Fahrenheit) can help in decreasing the risk of Bacillus Cereus
- One should ensure that the food is maintained either at a temperature below 4°C or above 60°C.
- The freezing or Reheating of any foods that have been left out in normal temperature for more than two hours increases the risk of illness.
- The studies explain that the reheating of food to a temperature at or above 165 F (74 C) for 15 seconds can kill the cells but not the toxins. The foods having chances of being contaminated should be thrown out.
- Experts say that Bacillus cereus naturally grows on the uncooked rice grains. The spores generated by the bacteria are resistant and can easily survive the cooking process.
- During reheating the food, one should ensure that the temperature of heating goes at least up to 74°C.
B. cereus is a toxin-producing bacteria and can contaminate food. Psychrotrophic strains of Bacillus Cereus has highly affected the dairy industry.
Food poisoning associated with Bacillus Cereus is highly underestimated in official statistics as it is not reportable generally. It can cause complications in only a few cases.
The minimum infective dose for diarrhoeal type food poisoning is 105 to 107 Bacillus Cereus cells
Bacillus Cereus causes two different types of food poisoning. These are one diarrhoeal due to enterotoxins and emetic due to a preformed cyclic peptide.