Salmonella Revision: Source, Symptoms and Control

Salmonella is an important example of a food poisoning bacterium for GCSE Food Preparation and Nutrition. In this revision guide, you will learn where salmonella comes from, how it can spread, the symptoms it may cause and how food handlers can control the risk. The key idea is to prevent contamination, stop bacteria multiplying and destroy bacteria through safe preparation and cooking. These points link directly to practical work, such as handling raw chicken, preparing egg dishes and storing leftovers. Food safety guidance can change, so always check current advice from the Food Standards Agency and the official AQA specification before relying on specific procedures.

What is salmonella?

Salmonella is a type of pathogenic bacterium. Pathogenic means capable of causing disease. If salmonella gets into food and is then eaten, it can cause food poisoning, known as salmonellosis.

Salmonella cannot usually be seen, smelt or tasted in food. This is why a food looking fresh does not prove that it is safe. Good food safety practice is needed at every stage, from buying ingredients to serving a finished dish.

Where does salmonella come from?

Salmonella may be present in the intestines of animals and can contaminate food during slaughter, collection, processing or preparation. Common food sources include:

• raw poultry, such as chicken and turkey
• raw meat
• raw or lightly cooked eggs and dishes made with them
• unpasteurised milk and products made from it

Raw ingredients are not automatically unsafe, but they need careful handling. For example, raw chicken juices could contaminate a salad, bread or a cooked dish if the same chopping board, knife or work surface is used without effective cleaning between tasks.

How salmonella spreads

Cross-contamination is the transfer of harmful microorganisms from one food, person or surface to another. Salmonella can spread when:

• raw poultry is stored above ready-to-eat food in a refrigerator
• raw meat is prepared on a board that is then used for cooked food
• hands are not washed after handling raw eggs or meat
• cloths, utensils or equipment are dirty
• cooked food is placed on a plate that held raw ingredients
• raw food touches food that will not be cooked again

Ready-to-eat food is food that will be eaten without another step that kills bacteria, such as cooking. Examples include salad, fruit, bread and a cooked dish that has cooled ready for serving. These foods need particular protection from raw ingredients.

Conditions that allow bacteria to multiply

Bacteria need suitable conditions to grow and multiply. In food safety, remember the main factors as:

Food safety controls work by removing or limiting one or more of these conditions. A refrigerator slows bacterial multiplication, but it does not make food sterile. This is why storage times and use-by dates still matter.

Symptoms of salmonella food poisoning

Symptoms can include:

• diarrhoea
• vomiting
• stomach cramps or abdominal pain
• fever
• nausea

Symptoms may not start immediately after eating contaminated food. The person’s age, health and the amount of bacteria consumed can affect how ill they become. Food poisoning can be especially serious for young children, older people, pregnant people and anyone with a weakened immune system. Anyone who is seriously unwell should seek appropriate medical advice.

How to control salmonella

Prevent contamination

• Wash hands thoroughly before preparing food and after handling raw meat, poultry or eggs.
• Keep raw ingredients separate from ready-to-eat food.
• Use suitable equipment and clean work surfaces between preparation tasks.
• Store raw meat and poultry in sealed containers and follow current refrigerator-storage advice.
• Keep pets and unnecessary items away from food preparation areas.
• Do not prepare food for others if you have symptoms of food poisoning. Follow current official guidance about returning to food handling.

Control bacterial growth

• Follow storage instructions and use food by the date shown.
• Keep chilled foods chilled and avoid leaving high-risk foods at room temperature for longer than necessary.
• Cool leftovers safely and promptly, following current Food Standards Agency guidance.
• Keep food covered to protect it from contamination.

Destroy bacteria by cooking

Thorough cooking can destroy salmonella. For example, poultry and dishes containing egg need to be cooked properly so that the centre is not undercooked. Do not rely only on the outside colour of meat. Use the current official guidance for cooking and reheating, because food-safety recommendations can be updated.

Cooking will not make food safe if it becomes contaminated again afterwards. For instance, cooked chicken placed on the plate used for raw chicken could be recontaminated. This is why hygiene, separation, cooking and safe storage must work together.

Exam-ready summary

• Salmonella is a pathogenic bacterium that can cause food poisoning.
• Important sources include raw poultry, raw meat, eggs and unpasteurised milk.
• It can spread by cross-contamination from hands, equipment, surfaces and raw food juices.
• Symptoms may include diarrhoea, vomiting, abdominal pain, nausea and fever.
• Control salmonella by preventing contamination, limiting bacterial growth and cooking food thoroughly.
• Protect ready-to-eat food because it will not receive another cooking stage.
• Explain the reason for each control rather than simply listing hygiene actions.

For specification revision, compare your notes with the official AQA Food Preparation and Nutrition specification. Food-safety guidance can change, so check current information from AQA, the Food Standards Agency, NHS or GOV.UK before practical work.

Quick retrieval questions

1. What does pathogenic mean?
2. Name three possible sources of salmonella.
3. What is cross-contamination?
4. Why are ready-to-eat foods vulnerable?
5. Give one control for contamination, one for bacterial growth and one for destroying bacteria.