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Useful and Harmful Microbes

In this lesson, students will be introduced to four different types of microbes: bacteria, viruses, fungi, and protozoa/parasites. They will learn that microbes can be harmful (i.e., cause food poisoning) and useful (i.e., used to ferment food).

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Learning objectives
All students will:
  • Foodborne illness is caused by microbes, of which there are four different types
  • The difference between viruses, bacteria, parasites, and fungi
  • There are useful microbes in food
  • The importance of handling food correctly to avoid foodborne illness
Background Information

Food can contain useful and harmful microbes, as well as those associated with food spoilage. It is harmful microbes that can be associated with foodborne illness or ‘food poisoning’. The top five foodborne microbes in Europe account for about 70% of the health burdens related to foodborne illness and these include; Norovirus, Toxoplasma gondii, Campylobacter jejuni, Campylobacter coli. Salmonella enterica, and Listeria monocytogenes. Other microbes such as Bacillus cereus and Escherichia coli have also been associated with serious cases of foodborne illness.

These microbes can be found in raw meats, in eggs without a British Lion mark or equivalent quality marking outside of the UK, some dairy products, on the surface of fruits and vegetables, in dried food like pasta and rice or in ready to eat foods such as sandwiches and desserts.

Symptoms can include diarrhoea, stomach cramps, fever and vomiting and some foodborne illness may even result in death – though this is rare. The symptoms of foodborne illness usually start within a few days of eating the food that caused the infection and can usually be treated at home with rest and fluids.

Not all microbes associated with food are harmful. Useful microbes can be used to make food and drink, e.g., the yeast Saccharomyces cerevisae is used to make bread and beer. Lactobacilli bacteria are used in yoghurt and cheese making.

There are important steps you can take to prevent foodborne illness and spoilage that apply at all stages in the journey of food, from the shop to our plates:

  1. Keep clean: maintaining hand and surface hygiene is the best way for avoiding foodborne microbes entering our food
  2. Maintain the cold chain: keeping food in the fridge or freezer slows the growth of bacteria but does not stop it. Minimise the time food spends outside of the fridge or freezer
  3. Prevent cross-contamination: preventing harmful microbes found on food from spreading to other foods (for example via our hands or kitchen utensils) and causing illness when those foods are eaten
  4. Cook food such as meat thoroughly
  5. Follow the advice on labels: labels placed on foods are used to determine when it is safe to eat the food, or when the quality of the food is at its best

Main activity:
  • A matching activity to revise microbes
Main Activity video
Extension activities:
  • A case study to start a discussion about how microbes can cause foodborne illness
  • A research group task to allow students to work on a poster or fact file on one of the top five pathogens
Curriculum links


  • Health and prevention
  • Healthy eating

Supporting Materials
Teacher sheets
Useful and harmful microbes teacher guidance
Student worksheets
SW1 Useful and harmful microbes
SW2 Useful and harmful microbes
SW1 Useful and harmful microbes - answers


This resource was developed through the SafeConsume project, and funded by the European Union's Horizon 2020 research and innovation programme under grant agreement No 727580. Find out more about our partnerships on the Collaborating Projects page.

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