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Microbial contamination of food is almost inevitable owing to the ubiquity of microorganisms – which are found everywhere and even where life rarely exists. When food becomes contaminated, it will lead to food spoilage, and such food will no longer be fit for consumption. The soil, air, water, animals and animal products, plants and plant products, food handlers, food processing equipment and food storage vessels or platforms are some typical examples of various sources of microbial contamination of food and food products; and this is possible because these surfaces and sites harbour some significant amount of microorganisms. Microbial contamination of food and food products are major sources of human infections including food-borne diseases and food intoxifications or food poisoning; and these health conditions have caused significant morbidity and mortality amongst human populations. Owing to their nutritive constituents, foods and food products are suitable substrates for the growth of microorganisms inclusive of bacteria and fungi that cause food spoilage and food borne illnesses.   


The soil is ubiquitous with microorganisms; and this includes microbial normal flora of the soil and other microbes that contaminate it either from sewage or animal dung’s. The soil contains a huge diversity of microorganisms including bacteria, fungi and algae; and majority of these microbes play significant industrial roles including their usage for the production of antibiotics and other food products, vitamins and amino acids. However, the soil also harbours some dangerous microbes that could contaminate food and food products during and after production or processing. Most of the raw materials for food production are sourced from the soil; and when these materials are not properly washed and processed, they could serve as route via which foods and food products become contaminated. And contaminated foods and food products portend danger and other health problems to the consumers.    


The gastrointestinal tract (GIT) of animals is inundated with enteric bacteria and coliforms which are key indicator organisms for assessing the microbiological quality of food and food products as well as other materials and environments. When raw materials of animal origin are not well processed or washed in the course of food production, they could serve as potential sources of microbial contamination of food and food products. This normal flora of animal gut or GIT could also contaminate food when animal dung’s or their products come in contact with food or food products during production. 


The atmosphere or air that we breathe is also inundated with enormous diversity of microbes inclusive of those that are spore forming microorganisms. The air is naturally antagonistic to the survival of microorganisms owing to its dry nature. However, some microbes are capable of forming spores which allows them to withstand the dry nature of the atmosphere until they find a suitable environment (e.g. food) where they can thrive. The atmosphere is the major source of airborne pathogenic microorganisms inclusive of bacteria and fungi that cause food spoilage and foodborne diseases or infection. Air is a good medium for the dispersal of microbes to suitable environments such as food where they can colonize and begin to multiply. Maintaining good air quality is thus a critical factor in most food processing plants or industry due to the role they play in food contamination.    


Water is another environment that is inundated with different diversity of microorganisms including bacteria and fungi. Some foods especially sea foods such as crayfish, lobsters, oysters, fishes and shellfish amongst others could serve as route via which food borne diseases and pathogens can be transmitted in human populations; and this is usually the case when these foods are sourced from sewage- and faecally-contaminated water environments.     


Food handlers are humans that handle food and food products; and they play critical roles in the processing of food and the serving of food either at homes, in the restaurants, hotels or market places. The body surfaces of humans and even their internal body environment like other animals are inundated with a huge diversity of microbes that are either resident or transient in nature. It is advisable for food handlers to wear protective clothing’s during food processing because their direct body contact with raw materials for food production and even the equipment used in these processes could serve as possible sources of microbial contamination of food and food products.   


Equipment used for food processing and production constitute significant level and/or source of contamination in the finished food products. Unsterilized food processing equipment are potential sources of food contamination especially when they are not sterilized or cleaned properly before and after usage.


Plants are important raw materials for food production. However, plants could serve as medium of microbial contamination of food and food products since they contain filamentous fungi as normal flora on their surfaces. Plants originate from the soil – which is ubiquitous with a variety of microorganisms and other contaminating particles. It is vital to properly wash these materials to reduce their microbial load and remove soil particles that may serve as sources of contaminants to the production processes.  

Further reading

Bushell M.E (1998). Application   of   the   principles   of   industrial   microbiology   to   biotechnology (ed. Wiseman, A.) Chapman and Hall, New York.

Byong H. Lee (2015). Fundamentals of Food Biotechnology. Second edition. Wiley-Blackwell, New Jersey, United States.

Frazier W.C, Westhoff D.C and Vanitha N.M (2014). Food Microbiology. Fifth edition. McGraw-Hill Education (India) Private Limited, New Delhi, India.

Jay J.M (2005). Modern Food Microbiology. Fourth edition. Chapman and Hall Inc, New York, USA.

Bushell M.E (1998). Application   of   the   principles   of   industrial   microbiology   to   biotechnology (ed. Wiseman, A.) Chapman and Hall, New York.

Farida A.A (2012). Dairy Microbiology. First edition. Random Publications. New Delhi, India.

Nduka Okafor (2007). Modern industrial microbiology and biotechnology. First edition. Science Publishers, New Hampshire, USA.

Roberts D and Greenwood M (2003). Practical Food Microbiology. Third edition. Blackwell publishing Inc, USA.

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