Food Bugs

How bacteria grow

Bacteria need warmth and moisture to grow. They reproduce by dividing themselves, so one bacterium becomes two and then two become four and so on. In the right conditions one bacterium could become several million in 8 hours and thousands of millions in 12 hours.


This means that if a food is contaminated with a small number of bacteria and you leave it out of the fridge overnight it could be seriously contaminated by the next day. Then just one mouthful could make someone ill. If you put food in the fridge it will stop bacteria from multiplying.


Since you can't see, taste or smell bacteria, the only way that you can be sure that food is safe is to follow good food hygiene at all times.


The Food Hygiene Campaign is part of the Agency's strategy to reduce food poisoning. Food poisoning is measured by the number of cases that can be confirmed in a laboratory. The success of the Agency’s strategy will be measured by monitoring the annual number of laboratory-confirmed cases of the following five bacteria: campylobacter, salmonella, listeria, E. coli O157, Clostridium perfringens.

Types of bug

Campylobacter

Campylobacter is the most common identified cause of foodborne disease. It has been found mainly in poultry, red meat, unpasteurised milk and untreated water. Although it doesn't grow in food it spreads easily, so only a few bacteria in a piece of undercooked chicken could cause illness.

Campylobacter infections don't usually cause vomiting, but diarrhoea can be severe and bloody with abdominal cramps.


Clostridium perfringens

Clostridium perfringens is found in low numbers in many foods, particularly meat and poultry and their products. It is also found in the soil, the intestines of humans and animals, in sewage and in animal manures.

Infection with Clostridium perfringens normally causes diarrhoea and severe abdominal pain. It may occasionally cause nausea but it rarely causes vomiting or fever.

Unlike many other types of bacteria that cause foodborne disease, Clostridium perfringens isn't completely destroyed by ordinary cooking. This is because it produces heat-resistant spores.

The bacteria are killed at cooking temperatures, but the heat-resistant spores they produce are able to survive and may actually be stimulated to germinate by the heat. If the food is not eaten at once but is allowed to cool slowly, the bacteria produced when the spores germinate multiply rapidly. Unless the food is reheated so that it is piping hot (at least to 60°C and preferably to 75°C), the bacteria will survive. After ingestion, if there are sufficient numbers present, the bacteria will produce toxins and the toxins will cause symptoms.

Foods most likely to be associated with Clostridium perfringens food poisoning are those that are cooked slowly in large quantities and left to stand for a long time at room temperature.


Salmonella

Salmonella is the second-most-common cause of food poisoning after campylobacter. It has been found in unpasteurised milk, eggs and raw egg products, meat and poultry. It can survive if food is not cooked properly.

Salmonella can grow in food. If a small number of bacteria are present in a food, they will multiply unless it is chilled.

People infected with salmonella should be particularly careful with personal hygiene because they could infect another person who comes into direct contact with them. For example, if a carrier doesn't wash their hands properly after going to the toilet, they could have bacteria on their hands.


Listeria

Listeria monocytogenes can cause illness in certain groups of people, such as pregnant women, unborn and newborn babies and people with reduced immunity, particularly those over 60 (these could include people who've had transplants, are taking drugs that weaken the immune system or with cancers affecting the immune system, such as leukaemia or lymphoma). Among these vulnerable groups, the illness is often severe and can be life-threatening.

Listeria has been found in certain chilled ready-to-eat foods, such as pre-packed sandwiches, butter, cooked sliced meats, smoked salmon, soft mould-ripened cheeses and pâtés. Eating food containing high levels of Listeria monocytogenes is usually the cause of illness.

Vulnerable people should avoid eating pasteurised and unpasteurised cheeses such as Camembert, Brie or chevre (a type of goats' cheese), or others that have a similar rind, soft blue cheeses, and all types of pâté, including vegetable.

Special care should also be taken to follow the storage instructions on the food label. Chilled foods should be kept out of the fridge for the shortest time possible and you shouldn't use food after its 'use by' date.
 

E. coli

Most strains of E. coli are harmless, but those that produce verocytotoxin (called verocytotoxin-producing E.coli, or VTEC) can cause severe illness. In the UK, the most common type is E. coli O157, but in other countries other types such as E. coli O111 and E. coli O26 are more common.

E. coli O157 and other VTECs have been transmitted most commonly through undercooked minced beef and milk that is unpasteurised, inadequately pasteurised or contaminated after pasteurisation.

It's also possible to become infected by direct contact with infected animals or people, and by contact with land contaminated with animal faeces.

Common symptoms of E. coli O157 and other VTECs include bloody diarrhoea and abdominal cramps. The illness can also have very serious complications, including kidney failure, severe anaemia and neurological problems. Sometimes infections can lead to death.

Source:  Eat Well Gov.UK