Bacteria – introduction

Urgh! Germs. Bacteria are tiny living organisms which are so small you can’t see them without a microscope. If you do see them through a microscope they are usually round or rod-shaped. They’re often called “germs” in everyday language.

Bacteria are everywhere – in the soil, dust, water, in the air, and on our bodies. Don’t worry too much – not all bacteria are harmful.

Most bacteria are harmless, and some are even beneficial to us. Some harmless bacteria are used to manufacture food such as cheese and yoghurt. But not all are so helpful.

Some of the bacteria bad guys cause food to smell, lose its texture, and decay. These are referred to as “food spoilage bacteria”. They may not actually damage your health, but they’ll spoil the flavour and the appearance your food, making it inedible.

Some bacteria ARE harmful, and you need to be sure to avoid them. Organisms – including bacteria which cause disease are called “pathogens”. Unfortunately, there’s often no sign that they’re present; they may not change the appearance, smell or taste of the food at all.

Usually they need to multiply to large numbers before they can cause illness – so be sure to store your food properly and don’t let the little bu99ers multiply!

There are some exceptions. Some are dangerous even in small numbers. Campylobacter, for example, a bacterium which can lead to gastroenteritis, only needs small numbers to cause infection. This can be dangerous for vulnerable groups such as young children and elderly people.

The good news is that campylobacter and many others can easily be destroyed by heat. As long as your food is cooked through to 75°C/165°F, you’ve nothing to worry about from campylobacter. (But the fact that campylobacter is the biggest single cause of acute bacterial diarrhoea in the UK suggests that too many people are still ignoring this advice.)

Now we’ve got the real nasties. Some bacteria are capable of forming a protective covering for themselves – spores. (Technically, they’re endospores – see Mike K-H’s comment below.)

Spores enable bacteria to remain alive but inactive in conditions where you might expect bacteria to be killed. Then later, they can come back to haunt you! Change their conditions and they can turn back into the more usual type of bacteria and multiply rapidly.

Spores can stand high cooking temperatures and can survive situations where you’d not expect them to. Bacillus cereus, present in uncooked rice, is a particular danger. The spores can withstand boiling, even the prolonged boiling needed to cook rice. If the rice is allowed to stand at room temperature, the spores can then germinate and multiply. In this situation, reheating the rice won’t be enough to kill the bacteria – which can mean a nasty bout of vomiting later on.

If you are determined to go ahead and keep rice for reheating, then the advice given by food safety agencies is to cool it as quickly as possible, keep it in the fridge, and throw it away if it’s not eaten the next day.

But always stay aware that you cannot always see or smell bacteria, so the best way to stay safe is by following best procedures when preparing, handling, or storing food.

This is Chapter Two, Part One in a series of articles broadly similar to the course offered by the Royal Society for the Promotion of Health for its Food Hygiene Certificate.
Part Two: How bacteria grow

Chapter One: Food Poisoning
Chapter Three: Hygiene Control and Personal Hygiene
Chapter Four: Pest Control
Chapter Five: Kitchen Layout and Design
Chapter Six: Temperature Control
Chapter Seven: Cleaning the Work Area