Bacillus cereus is often present in rice, dried potato flakes and powdered dairy products. This bacteria can make people sick if these foods aren't safely handled after being cooked or rehydrated. Find out how Bacillus cereus can make you ill and how to avoid infection.
Symptoms of Bacillus cereus infection
Bacillus cereus infection can cause nausea, vomiting and diarrhoea. Illness usually occurs 1 to 6 hours after eating contaminated food.
How you can be exposed to the bacteria?
Most illnesses from Bacillus cereus are caused by eating contaminated rice or starchy foods such as potato flakes and pasta. Powdered dairy products are also a source of Bacillus cereus. The bacteria grow to dangerous numbers when these foods are cooled too slowly, or are not stored in a fridge.
Further cooking or reheating will not get rid of this toxin, which can withstand heating for 90 minutes at 126 degrees Celsius.
Bacillus cereus can also survive in dried raw rice by producing resistant spores. If rice is cooled too slowly after cooking. For example, if you have too much rice in a very large pot, the spores germinate, and the bacterial cells multiply and produce a toxin.
In dried potato flakes
Bacillus cereus occurs naturally in most foods, but usually not in high enough numbers to make people sick. Bacillus cereus survives the drying process by producing resistant spores. When potato flakes are rehydrated, the spores can germinate and bacteria multiply. These can produce a toxin if the food is not eaten immediately, and is left sitting at room temperature for a few hours.
Again, further cooking or reheating will not get rid of this toxin.
How to avoid infection
Always follow safe practices when cooking and storing rice and dried potato flakes. Don't cook and cool rice in large quantities – separate into smaller amounts so that it will cool quickly.
Make sure the cooked product is eaten immediately or either:
- kept hot at above 60 degrees Celsius, or
- cooled and stored in the fridge until used.
If rice has been cooked for sushi or egg-fried rice, cool it in the fridge until it is ready to use. Sushi rice usually contains sushi vinegar and a mixture of sugar and salt, which helps to prevent the growth of the Bacillus cereus.