Accepta Newsletter #8: Salmonella, Listeria, Legionella Control...

A Bug's Life - Part 2

This article follows on from "A Bug's Life" (Issue 7), taking a closer look at five of the most common bacteria that cause food poisoning: Salmonella, Listeria, E.coli O157, Clostridium Perfringens and Campylobacter.

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 is present all around in the environment. It has also been found in low numbers in many foods. In certain foods, such as soft mould-ripened cheeses and pâtés, it may be present in higher numbers. Eating foods containing high levels of listeria monocytogenes is generally the cause of illness.

Listeria monocytogenes usually causes illness in vulnerable groups such as pregnant women, babies, the elderly and people with reduced immunity. Among these groups, the illness is often severe and life threatening.

E. Coli O157

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.

E.coli O157 has been transmitted most commonly through undercooked minced beef and milk that is raw, 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 include bloody diarrhoea and abdominal cramps. The illness can also have very serious complications, including kidney failure, severe anaemia and neurological problems. Sometimes Ecoli O157 infections can lead to death.

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 60oC and preferably to 75oC), 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.

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.

©Crown copyright. This article was reproduced with the kind permission of the Food Standards Agency - www.foodstandards.gov.uk

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