|Cheese is considered to be a safe food due to its acidity, salt content and low water activity. Enormous quantities are made and eaten each year without problems. The greatest risk of food poisoning comes from three types of bacteria, although others have been implicated in cases throughout the world. |
Salmonellae can grow in cheese during manufacture and storage, but they are unlikely to be present if the cheese has been made from pasteurised milk. Most cases of illness have been due to the cheese being contaminated due to poor hygienic practices.
Listeria monocytogenes is more likely to be found in soft, mould ripened cheeses which are still made with raw milk in some countries. This bacterium does not generally affect healthy people, but the young, elderly, immuno-compromised and pregnant women are at risk. The bacteria can cause flu-like symptoms, blood poisoning or meningitis and can harm unborn babies.
E. coli O157 is acid tolerant, unlike most coliforms, and may be found in cheese that has been badly handled or has been made from raw milk. It can cause severe illness in the young, elderly or immunocompromised.
Control of unwanted microbes in cheese is achieved by good manufacturing practice and attention to hygiene. Sometimes preservatives are added to cheese. Storage and packaging are also important.