We live in a world that is dominated by bacteria, which inhabit every conceivable nook and cranny including on us, and inside us. Usually, this is not a problem, but when the balance is disturbed it causes illness

We have evolved to live in harmony with most of the bacteria that we are surrounded by. Helpful bacteria, such as those found in live yoghurt and sauerkraut, are our friends and support good health.

However, there are still a whole host of unfriendly, or pathogenic, bacteria which cause infections and food poisoning. Bacterial food poisoning symptoms typically appear within an hour or up to 72 hours (or sometimes longer).

The delay in timing depends on circumstances, and happens because the bacteria multiplies to a point where it causes illness.

Symptoms can include nausea, vomiting, stomach cramps, diarrhoea (sometimes bloody), or fever. If the food poisoning has come from a restaurant or other food supplier it should always be notified to your doctor who is meant to report it to the health authorities to prevent further outbreaks.

The best way to avoid most of these pathogenic bacteria causing problems is via careful food sourcing, storage and preparation. It also helps to keep your immune and digestive health in tip-top balance so that your healthy bacteria, which colonise your body (mainly in your bowels) are able to fight the fight for you and keep pathogenic bacteria from getting too much of a foothold.

If you contract food poisoning your doctor will probably prescribe antibiotics to fight any serious bacterial infection and recommend that you drink sufficient water to stay hydrated if you have diarrhoea. The following are the most common bacterial infections:

Campylobacter

Campylobacter is the most common bacterial causes of diarrhoeal illness with 40,000 cases each year in the UK.

The organism can cause diarrhoea (including bloody diarrhea), cramping, abdominal pain and fever as well as nausea but does not usually cause vomiting. The illness may last one week. Rarely, it is linked to triggering arthritis or Guillain-Barre syndrome, an autoimmune disease which can lead to paralysis.

Campylobacter tends to strike in single, sporadic cases rather than large outbreaks. Most cases are associated with handling raw poultry or eating raw or undercooked poultry meat. It is also found in unpasteurised milk and untreated water.

Cooking poultry thoroughly is essential. It is important to keep separate chopping boards for meat, bread and vegetables. People often also don't realise that if they touch, for instance, contaminated poultry (which is later cooked properly) that they can still spread the bacteria via chopping boards and utensils.

Salmonella

Salmonella, the second most common food bacterial infection, can cause bloody diarrhea in humans. Some 13,000 cases of salmonellosis are reported in the UK each year, although because milder cases are not diagnosed or reported, the actual number of infections may be several times greater.

A rare form of salmonella comes from reptiles, such as snakes, kept as pets who harbour it on their skin.

The risk of infection is greater in the summer than winter because the bacteria multiply in the warmth. Children, the elderly and those with compromised immune systems are most at risk of serious complications.

Infection comes from eating contaminated foods, usually undercooked minced beef, eggs, improperly pasteurised dairy products, undercooked pork and poultry products. In the UK, Lion Mark eggs are all from flocks that are vaccinated against salmonella.

Prevention methods include cooking poultry and meat thoroughly, with the added caution not to eat raw eggs or anything containing raw eggs (such as fresh mayonnaise, lightly boiled eggs and home made ice-cream). Soft whipped ice cream from touring vans can also be a source. Breastfeeding infants can also help to prevent infection in the babies as it helps their immune health.

E. Coli 0157:H7

There are many strains of the bacteria known as Escherichia coli, or E. coli. Most are harmless, four or five strains can cause disease, and one, in particular, can be serious or even fatal.

Usually infection with E. coli 0157:H7 results in bloody diarrhea lasting two to eight days. But sometimes there is kidney failure. The UK incidence is about 700 cases annually.

E. Coli 0157:H7 has been implicated in several deadly outbreaks making it fairly high-profile compared to other more common infections. Most human infections result from eating undercooked minced beef (cattle carry the pathogen in their intestines).

It can also be acquired from consuming unpasteurised or contaminated dairy products, vegetables, or unpasteurised juice which might have been contaminated with manure (manure needs to be properly composted to make it a harmless fertiliser), person-to-person contact, and swimming in or drinking water contaminated with sewage.

The bacteria also lives in deer, goats and sheep and is a permanent resident of many petting zoos which is why they always emphasise washing hands after touching the animals.

There are ways to prevent transmission of the bacteria, namely good food hygiene and cooking meat thoroughly.

Listeria

Listeria infection is caused by eating food contaminated with the bacterium Listeria monocytogenes.

Pregnant women, newborns and adults with compromised immune system are more vulnerable to this infection, characterised by fever, muscle aches and sometimes nausea or diarrhea. The infection can spread to the nervous system, resulting in headache, confusion, loss of balance or convulsions.

About 130 people in the UK are diagnosed each year with listeriosis. It is particularly dangerous for pregnant women as it can affect the unborn baby.

Listeria is usually killed by cooking and pasteurisation but can be present in certain ready-to-eat foods such as pates and fast-food hot dogs. Pregnant women are advised to avoid unpasteurised cheeses, mould ripened cheeses such as Brie and Camembert, blue cheeses, pates of all descriptions, all of which can be sources of listeria.

Botulism

Botulism is a disease caused by the bacterium Clostridium botulinum. The organism produces a nerve toxin that can cause paralysis, including respiratory paralysis.

The organism thrives in environments lacking in oxygen, such as improperly canned goods, and botulism can be found in home-canned foods with low acid content, such as asparagus, green beans, and beets. When canned food doesn't reach the proper heat or pressurisation, there is a danger.

However, there is a low prevalence in the UK as bottling of produce at home is not common these days.

Another source of botulism is honey which is a risk for infant botulism. UK health authorities warn against giving honey to infants under the age of one as this can be a source of infection, and raw honey is a particular risk. Babies do not have sufficiently mature bowel bacterial colonies to fight the organism whereas an adult is less at risk.

Clostridium Perfringens

Mainly found in meat and poultry, but also in soil, sewage and manure. It causes diarrheoa, cramping and, sometimes, nausea. The spores (which are bacteria 'seedlings') are not destroyed by cooking even at high temperatures.

This means that bacteria can multiply in food left at room temperature. If the food is not then thoroughly reheated at high enough temperatures (heat can kill bacteria but not spores) then the bacteria remain to cause infection.

Shigella

Shigella is a bacteria found naturally in the intestinal tracts of humans. But people who eat food or drink water contaminated by Shigella can become ill with shigellosis. Food contaminated with Shigella usually comes from water polluted by human sewage or if handled by a person infected with Shigella, such as restaurant workers.