Bacteria: friend or foe? Part 7 of 11

Two classes of bacteria, Bacillus and Clostridium, will not die, like “normal” bacteria, if they are in adverse conditions. They enter a “Resilient Resistance 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 inactive. 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 instead 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 bought as a dry product. The 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 ingested, the acidic conditions of the stomach will prevent the spores from germinating and being processed with the rice for expulsion as feces. If the rice is cooked and cooled quickly for use the next day, the spores will not have time to germinate. After the rice is cooked, it should be placed under cold running water until cool to the touch and then refrigerated until used.

Some restaurants, cafes and takeaways prepare, and still do, rice for use the next day, letting it cool in the kitchen. Look at this scenario. The rice has been cooked and placed in a colander to drain. Until this time, the spores remain intact. As the rice slowly cools in the hot kitchen, 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 will become intoxicated. If the rice is reheated to provide a hot dish, perhaps egg fried rice, poisoning will result. Cooking will turn the bacteria present into spores, but heating will not deactivate the toxins, which cannot be detected through smell or taste.

60 people out of 200 who attended a local authority function in November 2009 became ill with symptoms of stomach aches and nausea. The main symptom was vomiting. The buffet meal included ham quiche, sausage rolls, egg mayo, risotto, ham and chicken sandwiches, chicken thighs, mixed seafood pizza, prawn and mushroom vol-au-vents, fruit trifle and fresh cream. The buffet had been prepared the day before by the local councilors and their wives in their homes and transported at 10:00 am on the day of the performance in unrefrigerated vehicles to the Civic Center. The buffet was left unrefrigerated in a room until it was required for consumption at 7.30pm. The first person became ill at 9:00 p.m. and most people became ill 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 specimens of people who had been ill and also from the remains of risotto. Therefore, risotto was the vehicle and rice the original source of the bacteria. The rice had been cooked at 12 noon the day before the performance. After cooking, it was allowed to cool to room temperature overnight. It was then transported without refrigeration. It was reheated with a microwave oven just before service.

The rice contained Bacillus cereus spores. Normal cooking is unable to destroy spores; in fact, the heat activates the spores so that, in slow and prolonged 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 cool the rice quickly, for example under cold running water. The rice should then be refrigerated below 5 ° C. The rice should then be fully reheated and should only be left at room temperature for a short period of time (maximum 30 minutes), during further preparation or waiting to be served. Even if you have some rice left over from a dinner plate, do not leave it out of the refrigerator, if you are going to eat it the next day it will poison you.