Home » Consumer Information » Food Safety » General Information » Harmful Bacteria

Harmful Bacteria

Most bacteria are harmless and some are even helpful to man. But a small important proportion can infect some foods, and when conditions are suitable they grow, produce toxins, and cause food poisoning. One of the best ways to stop these bacteria from reaching harmful levels is to inhibit their growth. They grow best between 5ºC and 63ºC. So foods should be kept either cold (below 5ºC) or hot (over 63ºC) to prevent growth.

Common Food Poisoning Bacteria:

Campylobacter:

Origin: These bacteria come from the gut of warm-blooded animals where they can live without causing any harm to their host. Foods of animal origin therefore act as routes of infection to man e.g. unpasteurised milk and raw meat and poultry.

Symptoms: Diarrhoea 1-7 days after eating contaminated food. May also have fever, abdominal pain and nausea.

Control: Campylobacter cannot grow at refrigeration temperature so numbers can be controlled by storing foods at low temperatures (less than 5ºC). It is also important to avoid drinking unpasteurised milk, and to use good hygiene to prevent cross-contamination between raw and cooked meat.

Salmonella:

Origin: Like Campylobacter these bacteria come from the gut of warm-blooded animals including humans. Some strains also cause disease in their host. Humans who harbour the bacterium without showing any symptoms of disease are called 'carriers' and should not work within food manufacturing, preparation or retailing. Foods which can contain Salmonella include raw poultry, poultry products, eggs and egg products, unpasteurised milk, raw meat and meat products.

Symptoms: Nausea, vomiting and diarrhoea 12-24 hours after eating contaminated food.

Control: Salmonella cannot grow at refrigeration temperature so numbers can be controlled by storing foods at low temperatures (less than 5ºC). Since eggs have been implicated in many cases it is advisable to cook eggs until the yolk is hard and avoid using cracked or broken eggs. It is also important to avoid drinking milk that has not been pasteurised, and to use good hygiene to prevent cross-contamination between raw and cooked meat and poultry.

Clostridium perfringens:

Origin: Again these bacteria come from the gut of warm-blooded animals and can also be found in soils and water. Like Campylobacter and Salmonella the bacterium can get into meat and meat products during processing.

Symptoms: Acute abdominal pain and diarrhoea with nausea 6-24 hours after eating contaminated food.

Control: Because Clostridium perfringens can produce very heat resistant forms (spores) control measures include adequate cooking (70ºC for 2 minutes), followed by fast and adequate cooling for large joints of meat. Also adequate reheating is important. Foods left standing at room temperature for long periods allows Clostridium to grow and produce toxins within the food. It is the toxin which causes the food poisoning. Again it is important to use good hygiene to prevent cross-contam i nation between raw and cooked meats.

Escherichia coli:

Origin: Verocytotoxin-producing E.coli (VTEC) - sometimes referred to as enterohaemorrhagic E.coli (IEHEC) originates in the gut of warm-blooded animals and can get into meat and meat products during processing. Can also be found in unpasteurised milk.

Symptoms: Not a very common illness, however, serious infections particularly in children may result. The 0 157-1-17 type is the predominant cause of human infections. Symptoms include a mild diarrhoea, with as few as 10 cells causing infection.

Control: adequate cooking of meat (70ºC for 2 minutes internal temperature) and pasteurisation of milk will protect consumers from infection. Hygienic food handling and good chilled storage conditions (less than 5ºC) are also essential to ensure that other foods do not become contaminated.

Staphylococcus aureus:

Origin: These bacteria can be found on the skin and within the moist lining of the nose, eyes and throat in humans. They are also present on cuts and boils. From here they can be transferred to foods by poor hygienic practices.

Symptoms: Nausea, vomiting, abdominal cramps and diarrhoea 1-6 hours after eating contaminated food.

Control: Good personal hygiene and high standards of hygiene when handling foods. Adequate cooking, reheating and good temperature control of foods during storage.

Viruses

Although the number of cases of food poisoning which are caused by the presence of viruses in food is easy to determine, food and water are recognised as important vectors for the transmission of viruses.

Chemicals

Occasionally chemical poisons can get into food. These can come from cooking utensils (especially with acid foods), and residues from pesticides, and insecticides which may have been used in cereal crops, fruit and vegetables. To minimise the risk from chemical food poisoning it is advisable to:

• Remove foods from cans once they have been opened.
• Wash fruit and vegetables before consumption.

Allergies:
Some people may suffer symptoms as a result of eating certain foods because they have an allergy. For example shellfish, strawberries and cheese are foods to which some people are allergic. These reactions are uncommon and are not due to contamination of the food.