Two classes of bacteria, Bacillus and Clostridium, will not die, like “normal” bacteria, if adverse conditions are encountered. They enter a “Resilient Resting Phase”. They produce an endospore. The spore forms inside the bacterial cell when the going gets tough and the rest of the cell disintegrates. Think of a spore as a dry, ungerminated seed. Without moisture, the spore will remain dormant. Provide moisture and the spore will germinate into a bacterial cell. Provide nutrients and a warm temperature and the cell will multiply. As they multiply, they release exotoxins, which are heat stable. We ingest spores daily, without any harm or consequence, since our digestive process is a very hostile environment for spores and they do not germinate, but pass directly through our system and are expelled with our feces. They can germinate and contaminate after defecation.
bacillus cereus it is a troublesome spore in rice. Rice is purchased as a dry product. Any spores present will remain as spores in the dry environment. If the rice is cooked and served hot, the spores will not have time to germinate due to the high temperature. If the rice is subsequently eaten, the acidic conditions of the stomach will prevent the spores from germinating and being processed with the rice to be expelled as faeces. If the rice is cooked and quickly cooled for use the next day, the spores will not have time to germinate. After cooking the rice, it should be placed under cold running water until it feels cool to the touch, then refrigerated until use.
Some restaurants, cafes, and take-aways have, and still do, prepare rice for use the next day by letting it cool on the stove. Look at this scenario. The rice has been cooked and placed in a colander to drain. Up to this point, the spores are still intact. As the rice slowly cools on the hot stove, it will reach an ideal temperature for the spores to germinate (body temperature). The spores germinate, the bacteria grow and produce toxins, yes, two different toxins, type A and type B. The longer the rice is left, the more toxins are produced. When the rice is served cold the next day, perhaps in a rice salad, the customer is poisoned. If the rice is reheated to provide a hot dish, perhaps egg fried rice, food poisoning will result. Cooking will convert any bacteria present into spores, but heating will not inactivate the toxins, which cannot be detected through smell or taste.
60 people out of 200 who attended a local authority function in November 2009 fell ill with symptoms of stomach ache and nausea. The main symptom was vomiting. The buffet meal included ham quiche, sausage rolls, egg mayonnaise, risotto, ham and chicken sandwiches, chicken thighs, mixed seafood pizza, shrimp and mushroom vol-au-vents, fruit trifle, and crème fraiche. The buffet had been prepared the day before by the councilors and their wives at their homes and transported at 10:00 am on the day of the performance in non-refrigerated vehicles to the Civic Center. The buffet was left unrefrigerated in a room until it was required for consumption at 7:30 p.m. The first person got sick at 9:00 p.m. and most people got sick between 9:00 p.m. and 11:00 p.m. All the people had eaten the risotto.
bacillus cereus it was isolated from the fecal samples of those people who had been ill and also from the remains of the risotto. The risotto was therefore the vehicle and the rice the original source of the bacteria. The rice had been cooked at 12:00 noon the day before the performance. After cooking it was allowed to cool to room temperature overnight. It was then shipped unrefrigerated. It was reheated in a microwave oven just before service.
The rice contained spores of Bacillus cereus. Normal cooking is unable to destroy the spores; in fact, the heat activates the spores so that, after long and slow cooling, they germinate and produce a large number of vegetative bacteria. Bacteria multiply and produce toxins (this is the main danger).
The main control is to serve the rice immediately after cooking or to keep the rice above 63°C before serving or to quickly cool it, for example, under cold running water. The rice should then be refrigerated to below 5°C. The rice should then be fully reheated and only left at room temperature for a short period of time (maximum 30 minutes), during subsequent preparation or while waiting to be served. Even if you have some rice left over from a dinner plate, do not leave it out of the fridge, if you are going to eat it the next day, it will poison you.