Food Poisoning Bacteria: Campylobacter and Salmonella

This lesson covers two of the most important food poisoning bacteria in the UK — Campylobacter and Salmonella — as required by the AQA GCSE Food Preparation and Nutrition specification (8585), section 3.4. You need to know the sources, symptoms, onset times, and prevention methods for each bacterium. These are among the most commonly examined food poisoning organisms.

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Food Poisoning: An Overview

Food poisoning is an illness caused by eating food contaminated with pathogenic bacteria (or their toxins), viruses, or other harmful substances. In the UK, the Food Standards Agency (FSA) estimates that approximately 2.4 million cases of foodborne illness occur each year.

Food poisoning is caused by:

• Eating food contaminated with pathogenic bacteria
• Eating food containing toxins produced by bacteria
• Eating food contaminated with viruses (e.g., norovirus)

The severity of food poisoning depends on:

• The type of bacterium or toxin involved
• The amount of contaminated food eaten
• The health and age of the person affected

Vulnerable Groups

Some people are at greater risk of serious illness from food poisoning:

Group	Why More Vulnerable
Babies and young children	Immature immune systems
Elderly people	Weakened immune systems
Pregnant women	Altered immune response; risk to unborn baby
People with weakened immune systems	Those with HIV/AIDS, undergoing chemotherapy, or taking immunosuppressant drugs

These groups are sometimes referred to by the acronym YOPI (Young, Old, Pregnant, Immunocompromised).

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Campylobacter

Campylobacter is the most common cause of food poisoning in the UK. The Food Standards Agency estimates that Campylobacter causes approximately 500,000 cases of food poisoning in the UK each year.

Sources of Campylobacter

Source	Detail
Raw poultry	The primary source — present on about 50% of chicken sold in the UK
Unpasteurised milk	Can contain Campylobacter from infected cattle
Untreated water	Contaminated by animal faeces
Raw meat	Especially liver and offal
Pets	Dogs, cats and farm animals can carry Campylobacter

How Campylobacter Spreads

Campylobacter is most commonly spread through:

1. Eating undercooked poultry — especially chicken that is pink inside
2. Cross-contamination — raw poultry juices contacting ready-to-eat foods, surfaces or utensils
3. Washing raw chicken — this practice splashes contaminated water droplets onto surfaces, hands and nearby foods (the FSA advises never to wash raw chicken)
4. Drinking unpasteurised milk or contaminated water

flowchart TD
    A["Raw Poultry<br/>(primary source)"] --> B["Undercooked<br/>chicken eaten"]
    A --> C["Cross-contamination<br/>via surfaces/utensils"]
    A --> D["Washing raw chicken<br/>splashes bacteria"]
    E["Unpasteurised Milk"] --> F["Consumed without<br/>heat treatment"]
    G["Contaminated Water"] --> H["Consumed without<br/>treatment"]

    B --> I["CAMPYLOBACTER<br/>FOOD POISONING"]
    C --> I
    D --> I
    F --> I
    H --> I

    style I fill:#e74c3c,color:#fff
    style A fill:#e67e22,color:#fff
    style E fill:#e67e22,color:#fff
    style G fill:#e67e22,color:#fff

Symptoms of Campylobacter Food Poisoning

Feature	Detail
Onset time	2–5 days after eating contaminated food
Duration	Usually 5–7 days, sometimes up to 10 days
Main symptoms	Diarrhoea (often bloody), severe abdominal pain and cramping, nausea, vomiting, fever, headache
Serious complications	Reactive arthritis (joint inflammation), Guillain-Barré syndrome (rare nerve damage)

Exam Tip: Campylobacter has a relatively long onset time (2–5 days), which is a distinguishing feature. If an exam question describes symptoms appearing several days after eating chicken, Campylobacter is likely the answer.

Prevention of Campylobacter

Prevention Method	Explanation
Cook poultry thoroughly	Ensure core temperature reaches at least 75°C — no pink meat, juices run clear
Do not wash raw chicken	Washing splashes bacteria onto surfaces; cooking kills bacteria
Prevent cross-contamination	Use separate chopping boards, utensils and storage for raw poultry
Store raw poultry correctly	Keep on the bottom shelf of the fridge in a covered container to prevent drips
Wash hands thoroughly	After handling raw poultry, use hot soapy water for at least 20 seconds
Use pasteurised milk	Avoid unpasteurised (raw) milk
Clean surfaces	Disinfect all surfaces and equipment that have been in contact with raw poultry

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Salmonella

Salmonella is the second most common cause of food poisoning in the UK. There are over 2,500 different strains (serotypes) of Salmonella bacteria. It causes approximately 33,000 confirmed cases per year in the UK, though the actual number is thought to be much higher.

Sources of Salmonella