Bacteria and food

By far the majority of food poisoning is caused by allowing bacteria to grow in foods to the point where they either make the food toxic (poisonous) by virtue of the by-products they secrete into the food, or because they grow to a population large enough to cause an infection in the consumer when the food is eaten.

In either case, the food has normally been "abused" in some way, perhaps leaving it in a car parked in the sun, or leaving food out on the kitchen table instead of putting it in the refrigerator.

Where do these bacteria come from? Well, bacteria are all around us - they help break down wastes, such as dead plant material or dead animals. If they didn't, life would soon become impossible on Earth, as all the organic matter would be locked up in these dead organisms. Bacteria are normal inhabitants of soil, the intestinal tract of man and animals and on the hides and hair.

Only a very small proportion of all the bacterial types on Earth are pathogens (organisms that can cause disease) and even fewer of those are transmitted in foods. In fact, the most important of these micro-organisms are members of just a few genera: Salmonella, Clostridium, Listeria, Escherichia, Campylobacter and Staphylococcus. There are others, but these will do for a start. Over time, this blog will contain lots of examples of these bacteria.

At first sight, the names of these groups are enough to put anyone off reading any further. But once you have seen them a few times, you'll recognize them (though only a microbiologist would think of calling them "Old friends"!)

I didn't really answer the question about where these things come from. Well, if they are in the environment, they'll get into food by many routes. They might get onto meat as the animal is slaughtered and butchered; careless food handlers might go to the toilet at break time and not wash their hands on their return - this could transfer bacteria from their own gut to the food when they handle it; flies and other insects may act as carriers or vectors to transfer bacteria from dirty places to food; vermin, such as rats and mice may also transfer bacteria around. Even birds may get into food premises and deposit droppings on surfaces, equipment or directly onto food. Sometimes the entry route is much less obvious, such as bird droppings on the roof getting washed by rain into a food premises through cracks in the roof.

All this comes down to keeping food clean, keeping it cold and not allowing it to be exposed to the environment for any longer than necessary. There is a lot to be said for cooking food and serving it straight from the pot.