Bacterial Contamination (AQA GCSE Food Preparation & Nutrition)

Revision Note

Naomi Holyoak

Written by: Naomi Holyoak

Reviewed by: Lára Marie McIvor

Bacterial contamination of food

  • Food that has been contaminated by harmful bacteria can cause illness

  • Examples of types of bacteria that can cause illness, and common sources of these bacteria, include:

    • campylobacter

      • Raw poultry and other meat, and untreated water and milk

    • e-coli

      • Raw beef, untreated water / milk and unwashed salad

    • salmonella

      • Raw poultry and untreated milk / eggs

    • listeria

      • Soft cheese, pâté and shellfish

    • staphylococcus aureus

      • Human / animal hair and skin

  • There are multiple ways in which food can become contaminated with harmful bacteria, as well as techniques that should be used to reduce the risk of contamination:

Source of contamination

Explanation

Prevention

Other food

Bacteria may be transferred directly from contaminated raw meat, eggs, seafood or vegetables

  • Separate raw food and cooked food during storage

  • Store defrosting raw food at the bottom of the fridge so that it does not drip onto other food

  • Wash raw vegetables thoroughly to remove soil bacteria

Surfaces or equipment

Bacteria may be transferred to food from improperly cleaned surfaces or equipment

  • Wipe surfaces thoroughly, e.g. with antibacterial spray, before preparing food

  • Clean equipment with hot water and soap after use

  • Use separate chopping boards for raw and cooked food

  • Use clean cloths every day

Person preparing food

People may have contaminated hands from touching other items, or they may have a bacterial infection that transfers to food from their hands or during coughing or sneezing

  • Wash hands before preparing food, in between preparing different foods and after touching the mouth/nose

  • Use a clean spoon every time food is tasted

  • Hold cooking utensils by the handles and not the part that touches food

  • Wear a hair net and clean gloves and cover cuts

Animal pests

Animals, such as rodents and insects, may transfer bacteria to food from their bodies, or via bodily waste such as urine or faeces

  • Prevent pests from entering the food preparation area by keeping doors and windows closed

  • Cover food waste bins and empty bins regularly so that pests are not attracted

  • Don't leave food out overnight

  • Cover food as it cools

Waste food and rubbish

Bacteria can be transferred to food from food waste bins and rubbish bins

  • Bins should have lids, and lids should be foot operated so that hands do not come into contact with bins and then with food

  • Bins should be emptied as soon as they are full

  • In addition to the contamination prevention methods described in the table, other risk-reducing procedures involve:

    • ensuring that food is heated to a high enough temperature during cooking to kill any bacteria

    • at-risk groups, such as the very young/old and pregnant women, avoiding high risk foods

    • food being served immediately after cooking or stored in a fridge / freezer

    • pasteurising milk, meaning that it is heated to a high temperature to kill bacteria, before it is sold in shops

    • vaccinating chickens against salmonella

Food poisoning

  • Eating food that has been contaminated by harmful bacteria can result in food poisoning

  • General symptoms of food poisoning include:

    • vomiting

    • nausea

    • diarrhoea

    • stomach pain

    • fever

  • Serious cases can result in death, especially in vulnerable individuals

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Naomi Holyoak

Author: Naomi Holyoak

Expertise: Biology

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.

Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.