Food & Cookery

Unit 1 / Session 1

Different types of bacteria

As you learned on the previous page, food safety is all about preventing contamination and the spread or growth of bacteria in the cooking environment. When bacteria is allowed to grow or transfer from one food to another, then there is a risk that it can cause food poisoning.

Bacteria need certain conditions in order to grow. One of the main factors in the growth of bacteria is temperature. Bacteria grow rapidly at 37°C, which is usually room or body temperature. Between 5 and 63°C, they continue to grow, although the rate at which they grow changes. This is known as the danger zone. At very cold temperatures, bacteria become dormant – they are not killed, but they do not grow or multiply.

Click through the slide panel below to find out more about the different types of bacteria which can cause food poisoning and the typical signs/symptoms of illness that may be caused.

  • E.coli

    Escherichia coli (E.coli) is a type of bacteria commonly found in human and animal intestines. There are many different types of E.coli – most are harmless, but some can cause serious food poisoning and infection. Some types of E.coli can cause gastrointestinal infections and the common mode of infection is by eating food that is contaminated with E.coli bacteria. Examples of foods where E.coli may be present include:

    • Raw leafy vegetables (that have not been washed).
    • Raw or undercooked meat.
    • Raw milk products.

    Symptoms of E.coli depend on the site of the infection and the type of E.coli that is causing the infection. Symptoms can take between 12 and 24 hours (or longer) to appear. Typical symptoms include stomach ache, fever, diarrhoea, vomiting, cystitis (an infection of the bladder) and even kidney damage or failure in severe cases. Symptoms usually last for up to seven days, but can last longer and become more severe in some cases.

  • Salmonella

    Salmonella is one of the most common type of bacteria which leads to food poisoning. The main sources of this bacteria are eggs and poultry so particular care should be taken when using these ingredients. Other foods where salmonella may be present include raw or undercooked meat, shellfish, unpasteurised milk and cheese and also contaminated raw fruits and vegetables.

    Symptoms of salmonella can appear between 12 and 72 hours after becoming infected. Typical symptoms include stomach ache, fever, diarrhoea and vomiting. Symptoms usually last for around 4 to 7 days.

  • Campylobacter

    Campylobacter can also cause food poisoning and this can be found in raw meat, poultry and shellfish. It is important to ensure that all meats are cooked to a safe temperature. Meats should be cooked to an inner temperature of at least 70°C and held at this temperature for at least 2 minutes. This ensures that all bacteria has been “killed”.

    Symptoms of campylobacter can appear within 2 to 5 days after becoming infected, but can take as long as 10 days. Typical symptoms include stomach pains/cramps, fever, nausea and diarrhoea (which may be bloody). Symptoms usually last for around 7 days.

  • Clostridium perfringens

    Clostridium perfringens is often found in foods that are kept warm for a long time before being served. These infections are usually linked to institutions (such as hospitals, school cafeterias, prisons and nursing homes) or events with catered food. This bacteria is often found in meats particularly beef and poultry, but also gravies, especially when made using the juices from the meat.

    Symptoms of clostridium perfringens can appear within a short time of becoming infected (often 12 to 24 hours). Typical symptoms include stomach ache and diarrhoea. Symptoms usually last for around 24 hours.

  • Staphylococcus aureus

    Staphylococcus aureus is another type of bacteria. These bacteria are commonly found in the nose, throat and on the skin. Poor personal hygiene can easily spread the bacteria to food – for example:

    • Sneezing over food.
    • Not washing hands after blowing your nose.
    • Coughing without covering your mouth and washing your hands.

    Typical food sources of staphylococcus can include:

    • Foods that involve hand contact during preparation and require no additional cooking – such as salads, bakery products, sandwiches, etc.
    • Milk and dairy products.
    • Meat and poultry.
    • Eggs and related products (such as mayonnaise).

    Symptoms of staphylococcus aureus can appear very quickly (often 1 to 6 hours). Typical symptoms include stomach pain/cramp, vomiting and a low temperature. Symptoms typically last for around 24 hours.

  • Listeria

    Listeria is a family of bacteria that contains ten different types (or species). One of these, listeria monocytogenes causes an illness in humans called listeriosis. Listeriosis is rare but can be very dangerous, and fatal in some cases. It can be particularly dangerous in older people, pregnant women and people with weakened immune systems (such as new babies). Listeria can live in food products such as meat, milk, butter, cream, yoghurt and vegetables.

    The spread of listeria can be avoided by washing all fruit, vegetables and salad ingredients fully before serving, cooking food thoroughly and serving it immediately, storing food in the correct refrigerated temperatures and keeping cooked and raw food separate at all times.

    Symptoms of listeriosis can take weeks or even months to appear! Typical symptoms are often very similar to flu symptoms – a high temperature, aches and pains, chills, fever, nausea and diarrhoea. These symptoms may only last for a few days.

  • Bacillus cereus

    This is a type of bacteria that produces toxins. These bacteria can be present in food and will multiply quickly at room temperature. The toxins they produce can cause nausea, vomiting and diarrhoea in humans. Common sources of bacillus cereus include rice, sauces, soups and other prepared foods that have been left out too long at room temperature (leftover food is also a common source of this bacteria).

    Symptoms of bacillus cereus can appear very quickly – often between 1 and 16 hours after infection. Typical symptoms are nausea, vomiting and diarrhoea. These symptoms may only last for a couple of days.