Sampling food for microbiological examination

Sampling food for microbiological examination

Officers from the Environmental Health Department undertake various routine sampling on a regular basis as detailed in the Division’s Food Sampling Policy.

There are four types of survey:

  • Walsall Local Initiatives
  • West Midland Food Surveys
  • National Food Surveys
  • European Food Surveys

Recent surveys have included meat products from manufacturers, burgers from street traders and takeaway meals.

Samples can be taken anonymously where an officer will purchase the food as an ordinary shopper unknown to the proprietor to check that the food is safe to eat.

Sometimes officers will identify themselves if further information such as storage conditions and temperatures are required. Samples can also be taken during routine inspections.

Samples of food and environmental swabs are submitted to an approved laboratory for examination.

Interpreting the results of food samples submitted for microbiological examination

Microbiological examination of food allows us to compare the levels of different bacteria found against those we expect to find in similar types of product. This helps us to assess whether the food was manufactured safely, handled hygienically, stored correctly or would be a risk to health if consumed.

Food is tested for some, or all, of the following bacteria:

  • Aerobic Colony Count
  • Eschericia coli
  • Enterobacteriaceae
  • Staphylococcus aureus
  • Clostridium perfringens
  • Bacillus cereus and Bacillus species
  • Listeria species
  • Salmonella species
  • Campylobacter species

The Aerobic Colony Count (ACC) is the total number of bacteria found in food. This examination is usually carried out on most foods, the exception being those foods that would naturally contain high levels of harmless bacteria e.g. salamis and milk products. A high ACC may indicate the product has been kept too long or that it has been left unrefrigerated. (Cold food) or not kept hot enough (Hot food)

Eschericia coli (E coli) is a bacterium, which is found in the gut of man and animals. It may be transmitted through faecal contamination at slaughter or through poor personal hygiene of food handlers. Their presence in cooked foods is indicative of poor personal hygiene – not washing hands after going to the toilet. There is a strain of E coli (EO157) which can cause serious illness, this bacteria is associated with meat e.g. burgers. The centre temperature of meats should reach at least 70ºC for two minutes, or equivalent temperature/time combination, or until the juices run clear.

Always ensure cooked foods are separated from raw.

Enterobacteriaceae includes bacteria that naturally inhabit the gut of man and animals but some are widespread in the environment. Enterobacteriaceae are useful indicators of hygiene and of post processing contamination of processed foods (i.e. from dirty machinery). Some of these bacteria are found in the environment and are therefore commonly found in salad/vegetable products or in cooked foods coming into contact with raw foods. It is essential therefore that salads are thoroughly washed, that all equipment be thoroughly cleaned and that cooked and raw foods are kept separate.

Staphylococcus aureus is bacterium that can produce a toxin in food that can cause food poisoning. This bacterium is found in the nose and mouth of humans and in uncovered wounds, cuts, spots, boils etc. The presence of these bacteria in food is usually due to poor personal hygiene combined with bad food handling practices. It is essential that hands are washed before handling food.

Clostridium perfringens is a bacterium that is found in the gut of animals and humans and in the environment. Some strains can cause food poisoning. Cooking rapidly for sufficient time will reduce its presence. It is also essential to prevent cross contamination from raw to cooked foods, especially uncooked meats.

Bacillus species and specifically Bacillus cereus, are food poisoning bacteria. Bacillus is widely distributed in the environment, and therefore found on grains, beans, pulses etc. It is essential that foods are cooked thoroughly, and if not being served immediately they must be cooled rapidly. This bacterium is usually associated with rice dishes where large volumes of food are produced in advance and may be cooled slowly over several hours. Refrigeration slows down growth.

Listeria species especially Listeria monocytogenes are found in the environment and is usually associated with salads, pates and soft cheese. Its presence in cooked foods can be an indication of insufficient cooking or contact with raw foods. This bacterium can grow well at refrigeration temperatures. It is essential that foods are cooked thoroughly and covered, and that all equipment and surfaces are cleaned thoroughly.

Salmonella species are food poisoning bacteria which can be found in the intestines of animals, humans and in polluted waters. Salmonella may be present in food due to insufficient cooking, cross contamination from raw food to cooked foods, the use of raw eggs in uncooked dishes or due to poor personal hygiene.

Some Campylobacter bacteria are known to cause food poisoning. This bacterium is found in the gut of some animals. Its presence in foods may be due to insufficient processing or cooking (e.g. unpasteurised milk, uncooked centre of rolled meat joints) or contamination by pets and other domestic animals. Food must be cooked thoroughly and once cooked not allowed to come into contact with raw foods or pets.

Reporting results to you

You will be notified of your results, usually in the following way:

Satisfactory : Means that the bacteria found were at acceptable levels;

Borderline of acceptability : There were higher than expected levels of bacteria. Proprietor must review systems of work to ensure that safe food is produced;

Unsatisfactory : This indicates problems with food handling. An urgent review of food handling procedures is required to ensure that food does not cause food poisoning;

Unacceptable / Potentially Hazardous : Consumption of this food may cause illness. Immediate action is required.

Follow these simple rules to help you to control the quality and safety of your food:

  • Identify all steps in your activities which are critical to food safety;
  • Put adequate safety controls in place;
  • Adequately train all staff in food hygiene;
  • Wash hands thoroughly before handling food, and again between handling raw and cooked foods, and after visiting the toilet;
  • Clean all equipment, utensils and preparation surfaces thoroughly;
  • Keep cooked and raw foods separate during preparation and storage;
  • Wash salads thoroughly;
  • Use food within its use-by-date and promptly use foods you have already prepared;
  • Keep food covered;
  • NEVER use raw eggs in food which is not going to be cooked e.g. mayonnaise, tiramisu;
  • Keep animals out of food preparation areas;
  • Use a thermometer to monitor temperatures and disinfect the temperature probe each time that it is used;
  • Cook food thoroughly (centre temperature more than 70ºC for 2 minutes) and serve. If hot-holding keep above 63ºC;
  • Re-heat food to at least 75ºC; only reheat food once;
  • Ensure any food requiring refrigeration is kept below 8ºC and not left out for long periods;
  • When preparing food in advance, ensure it is cooked thoroughly, cooled rapidly and stored in the fridge;
  • Avoid using left-overs

Contact us

Environmental Health
Civic Centre
Darwall Street

Telephone 01922 653010

This page was last updated on 18 July 2016