How does food become contaminated with harmful bacteria, and which bacteria cause food poisoning?
Bacterial contamination and the main food-poisoning bacteria (salmonella, E. coli, campylobacter, listeria, staphylococcus aureus), the sources and symptoms, and cross-contamination and how to prevent it.
A focused answer on bacterial contamination and food poisoning for OCR GCSE Food Preparation and Nutrition (J309), covering the main food-poisoning bacteria, their sources and symptoms, cross-contamination, and how to prevent it.
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What this dot point is asking
OCR wants you to know how food becomes contaminated with harmful bacteria, the main food-poisoning bacteria and their sources and symptoms, and what cross-contamination is and how to prevent it. This is among the most heavily examined parts of the course.
How food becomes contaminated
There are also physical contaminants (hair, glass, packaging) and chemical contaminants (cleaning products), but bacterial contamination is the main cause of food poisoning.
The main food-poisoning bacteria
Food poisoning is especially dangerous for high-risk groups: babies and young children, the elderly, pregnant women and people who are already ill, who can become seriously unwell.
Cross-contamination
To prevent cross-contamination:
- Separate raw and ready-to-eat foods; store raw meat below ready-to-eat food in the fridge so juices cannot drip onto it.
- Use separate, colour-coded chopping boards and knives (for example red for raw meat, green for salad).
- Wash hands thoroughly with soap and warm water after handling raw meat and before handling ready-to-eat food.
- Clean and sanitise surfaces and equipment between tasks, and use clean cloths.
- Prepare ready-to-eat foods first, or thoroughly clean down before switching.
Try this
Q1. Name the most common cause of bacterial food poisoning in the UK, found in raw poultry. [1 mark]
- Cue. Campylobacter.
Q2. Give two ways to prevent cross-contamination between raw meat and salad. [2 marks]
- Cue. Any two of: separate colour-coded boards and knives, store raw meat below ready-to-eat food, wash hands between tasks, clean and sanitise surfaces.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20186 marksExplain what is meant by cross-contamination and describe how a cook can prevent it when preparing raw chicken and a salad.Show worked answer →
A 6-mark free-response question.
Cross-contamination is the transfer of harmful bacteria from one food (usually raw, such as chicken) to another (often ready-to-eat, such as salad), directly or by way of hands, surfaces, equipment or cloths. It is dangerous because the salad is not cooked again to kill the bacteria.
To prevent it: use separate, colour-coded chopping boards and knives for raw chicken and for salad; prepare the salad first, then the chicken, or clean and sanitise surfaces and equipment in between; wash hands thoroughly after handling raw chicken; store raw chicken below ready-to-eat food in the fridge so juices cannot drip onto it; and use clean cloths.
Top-band answers (5 to 6 marks) define cross-contamination, explain why it is dangerous for ready-to-eat food, and give several clear prevention steps.
OCR 20204 marksName two bacteria that cause food poisoning and give a food source for each.Show worked answer →
A 4-mark question, two marks per bacterium-and-source pair.
Any two: salmonella (raw poultry, eggs); E. coli (undercooked beef, especially mince, and unwashed vegetables); campylobacter (raw poultry, unpasteurised milk); listeria (unpasteurised soft cheese, pate, chilled ready-to-eat foods); staphylococcus aureus (spread from the skin, nose and cuts of food handlers onto food).
Markers reward two correct named bacteria each with a sensible food source. A note that the symptoms are typically sickness, diarrhoea and stomach pain is a useful addition.
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