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What are Examples of Microorganisms?

Microorganism / March 8, 2018


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Micro-organisms, in relation to food, can have one of these 3 roles:

  1. Pathogenic micro-organisms can cause infections or intoxications
  2. Saprophytic micro-organism play a role in biodegradation and cause food spoilage
  3. Cultured micro-organisms like probiotic bacteria are used in food processing.

Pathogenic micro-organisms

Pathogenic micro-organisms cause food-borne infections or intoxication, and include bacteria, viruses, parasites and moulds. It is important to note that pathogenic bacteria and viruses usually do not cause food spoilage, their contamination cannot be seen nor tasted.

  • The main factors that contribute to occurrence of foodborne diseases are:
  1. The use of raw food and ingredients from unsafe sources
  2. Inadequate cooking or heat processing
  3. Improper cooling and storing, for example leaving cooked foods at room temperature for longer periods of time, or storing foods in large containers in the fridge
  4. Allowing several hours to pass between preparation and eating of food
  5. Inadequate reheating
  6. Improper hot holding, meaning below 65°C
  7. Food handling by infected persons or carriers of infection
  8. Cross contamination from raw to cooked food. For example by cutting vegetables for salad on a cutting board where you have cut raw meat before
  9. Inadequate cleaning of equipment and utensils


  • Campylobacter jejuni: Is a common cause of diarrhea humans as well as some animal species. The transmission can be by direct contact between humans and infected animals or their feces. More commonly, it is transmitted by the consumption of contaminated food or water, t person-to-person spread. The symptoms range from mild diarrhea to sever invasive disease which can include abdominal pain, fever, and blood and mucous in stools.
  • Non-typhi salmonellosis: There are more than 2000 serotypes of salmonella spp, of which only a few cause Salmonella gasteroenteritis in humans. The symptoms include acute watery diarrhea accompanied by nausea, cramps and fever. Blood in stool may occur. Animals are the main reservoir, and transmission occurs by ingestion of contaminated products. Foods especially at risk are poultry, meat, eggs and milk.
  • Salmonella typhi and paratyphi: Cause typhoid fever and paratyphoid fever respectively. Since the reservoir for both these bacteria are usually humans, transmission occurs mainly through person-to-person contact or contamination of food by food handlers.
  • Staphylococcus aureus: The source of this infection are humans. The bacteria are often found in smaller amounts in the nose and on the skin of clinically healthy people. Higher amounts can be found in lesions of skin such as infected eczema, psoriasis or any other pus draining lesion. These people should therefore not be handling food. Food poisoning caused by this bacteria is caused by heat resistant staphylotoxin, resulting in diarrhea, vomiting, cramps and fever. The symptoms start suddenly and usually disappear within 24 hours.
  • Escherichia coli: There are several serotypes, some of which are harmless to humans whereas others can cause gastroenteritis. Enterotoxigenic E.coli is the most common cause of traveller's diarrhea. The source is humans, and transmission usually occurs through contaminated food and water.

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