Bacterial food poisoning

This is one of the biggest – if not the biggest cause of food poisoning. It is used as an umbrella term to include a wide range of infections caused by various bacteria.

These include salmonella, campylobacter and E coli.

These bacteria live inside certain foods, for example, chicken, which, once they are consumed by a person, trigger a range of symptoms which we know as food poisoning.

These bacteria and their effect upon the human body are discussed individually as follows:

You may be familiar with a few of these bacteria but others less so. But what we do know is that even though these bacteria have their own individual characteristics, they are all capable of causing the same, unpleasant symptoms.

It does not matter whether you have food poisoning caused by e coli, listeria or salmonella when they all result in a miserable experience!

How do they trigger a bout of food poisoning?

What happens is this: you eat a food product, for example a piece of chicken or a beef burger which has, unbeknown to you, a type of bacteria which is known to cause food poisoning.

As you consume this food, the bacteria enter your body via your digestive system: or to be more precise your gastrointestinal tract. This is the part of the body where the symptoms of food poisoning develop.

Note: your gastrointestinal tract refers to your stomach and intestines.

The bacteria pass through the lining of the stomach and then attach themselves to soft tissues which line the wall of the intestines. Once there they proceed to multiply and destroy the cells which live within these walls.

They do this either by overwhelming these cells or by releasing a toxin which in some cases, can spread into the bloodstream. If it does so then there is the risk of it causing damage to other areas of the body.

Basically, some bacteria will remain in the intestines; others will produce a toxin which is absorbed into the bloodstream but some may access deep tissues within the body.

You can have two situations here:

  • Food is contaminated by bacteria which release toxins and cause food poisoning after consumption.
  • Toxins are produced by bacteria inside food whilst it is growing.

So, you can either ingest bacteria which then proceed to release toxins inside your intestines. This will result in symptoms of food poisoning appearing within 24 to 48 hours;


You consume food which already contains toxins that have been produced whilst the food was still growing. If this happens then the symptoms of food poisoning will appear that much quicker.

Ideal conditions for bacteria to grow

Bacteria love warm, moist environments. They respond to this by reproducing themselves, e.g. a single bacterium divides into two, and two bacteria divide into four and so on.

So as you can imagine, these bacteria can multiply into millions within a very short space of time.

Lets relate this to food: if a piece of meat or chicken is left standing on a kitchen worktop overnight instead of being stored in the fridge then by the morning, it will have become contaminated by millions of bacteria.

Anyone who picks up this tainted food and eats it will develop food poisoning – even from just a single mouthful.

But, this can be prevented. Bacteria do not like cold, dry places, e.g. a fridge, so storing food in this cold environment and at the correct temperature will stop these bacteria from multiplying.

The role of friendly bacteria

What are ‘friendly bacteria?’ You may have heard of this term but are wondering what these types of bacteria are and how they function.

One example you may be familiar with is a series of television advertisements which talk about friendly bacteria in relation to a brand of yoghurt drink.

Friendly bacteria occur naturally inside the body, in the large intestine and a section of the small intestine which lies furthest away from the stomach.

The reason they are not usually found in the stomach, oesophagus and initial section of the small intestines is due to gastric acid plus enzymes. These deter any growth of bacteria.

Friendly bacteria are kind to the body. They aid with digestion but more importantly, they act as a form of protection against unfriendly or harmful bacteria – such as those which cause food poisoning. These harmful bacteria invade the lining of the intestinal walls, destroying the cells within which leads to an infection.

Examples of friendly bacteria include:

  • Bacteroides
  • Lactobacillus (used in probiotic yoghurt)
  • Fusobacteria

Another type of friendly bacteria is E coli. This surprises many people who think of it in terms of causing food poisoning, but, there is more than one type of E coli bacteria. Many of these are harmless and are considered friendly bacteria.

However, there is one strain of E coli which is anything but harmless and can cause a variety of illnesses which includes food poisoning. This is the ‘E coli 0157:H7’ strain of bacteria.

Find out more about this type of bacteria within this section of the guide.

These friendly bacteria can be thrown off balance. This results in a situation in which there is a high proportion of one type of bacteria as compared to the others. Antibiotics are a cause of this as they do not tend to discriminate between the different types of bacteria.

Certain medical conditions can reduce the number of friendly bacteria or cause one species to dominate at the expense of others.

An imbalance can be resolved by the person ingesting probiotic supplements, such as yoghurt, which will correct this imbalance as well as adding a layer of protection.

You may be interested to know that friendly bacteria can be found inside the mouth and on the surface of the skin.

Food Poisoning Guide

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