The gut is often in constant touch with food throughout one’s life. While the importance of this process is self-evident, it also serves as a major route for introducing microorganisms into the gut. Studies have shown that an individual’s gut microbiota undergoes a marked change in composition when the child stops breastfeeding and starts feeding on the family diet. This change is attributed to the introduction of additional species of microorganisms to the gut microbiota. 

Food affects the microbiota in at least two ways. The first is by promoting or hindering the growth of microbial species already present in the gut. The second is by introducing new species that were not present before. This second method occurs via food that was contaminated in itself or food consumed with contaminated utensils or hands. According to the Food and Drug Administration (FDA), there are 48 million cases of foodborne illness each year in the United States. 

Microorganisms that find their way into the gut via food may be beneficial or harmful to the host. The following are common types of microorganisms that cause foodborne infections. 

Bacteria. These are the commonest organisms that cause foodborne illnesses. Millions of bacteria exist around you and on your body. Many are not harmful in their natural habitat but can cause illnesses in immunosuppressed individuals or when they are carried to other sites in your body. 

Bacteria in food can be killed through cooking. Freezing food stops their growth but does not kill bacteria. 

Viruses. Not all viruses are foodborne. Those that are foodborne such as Hepatitis A and Norovirus are mostly passed to others via food contaminated by handlers carrying the virus who do not observe strict hygiene. Viruses cannot be killed by heat or cold.

Protozoa. Protozoa are mainly beneficial to humans but may cause illness in humans. Those which commonly cause illnesses in humans include giardia and entamoeba which cause giardiasis and amoebiasis respectively. 

They are spread through the washing of food in contaminated water or poor hand hygiene by food handlers. 

Fungi. Fungi that are commonly carried by food to the gut grow as the mold that grows on bread. Cutting off the part where the mold is growing does not make the food safe because the fungi may have produced toxins which spread to sites beyond where the mold was visible. 


Canadian Institute of Food Safety. 6 Types of microorganisms that cause food-borne illness. Retrieved from 

FDA. Foodborne pathogens. Retrieved from

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