Food and Nutrition

Food Hazards (Microbiological)

Microbial hazard in food

Microorganisms in food

Organisms too small to be seen with the naked eye are called microorganisms. Microorganisms live everywhere: air, dirt, fresh and salt water, skin, hair, animal fur and plants. Microorganisms are classified into various groups and few of them important in foods include yeasts, molds, bacteria, viruses and protozoa.

Many microorganisms are beneficial. Addition of microorganisms in food is done intentionally in many cases e.g. Use of yeast in making beer, wine and other fermented beverages. Cheese, sour cream, yogurt and other fermented dairy products are produced by using different microorganisms. Although thousands of kinds of microorganisms exist, only a few pose hazards to humans. Therefore, when foods are processed and preserved, food processors and regulators need only be concerned with some microorganisms, particularly pathogens.

When microorganisms grow, they often produce by-products. More the growth, more the by-products.  Some by-products are desirable in the right foods e.g. when yeasts grow in dough, they produce carbon dioxide, acids and flavors. The dough rises and bread is produced by this method.

However, when the same yeasts grow and produce the same by-products in another food, such as fruit juice, it may not be desirable.  Then we call it spoilage. Such spoilage is undesirable, and processors strive to avoid it in food. In addition, some by-products produced by pathogens are toxic and can cause disease.

Spoiled food may not look, smell or taste good, but only food spoiled by pathogens or contaminated by toxic microbial by-products can make a person sick.  During processing of foods, amounts and types of microorganisms can be increased, held constant, reduced or destroyed.


Microbial spoilage of food


Even though processing can be used to destroy harmful microorganisms, many microorganisms can survive the treatment and continue to live.  E.g. Milk is pasteurized, or heat-treated, to destroy pathogens. After pasteurization, milk is safe to drink even though nonpathogenic microorganisms survive.

Some preservation methods such as drying or smoking, controls the water or nutrients in food making these essential elements unavailable to microorganisms.

Microbiological hazards

Hazard refers to anything present in food with the potential to harm the consumer, either by causing illness or injury. It can be biological, physical and chemical. Biological hazards mainly involves microbial hazards involving the microorganisms.

Microbiological hazard occurs when food becomes contaminated by microorganisms found in the air, food, water, soil, animals and the human body. Many microorganisms are beneficial, however under certain conditions, some microorganisms may cause food-borne illness. Microbiological hazards include bacteria, yeasts, molds, viruses, parasites and worms etc.

Microbiological hazards are considered to be a major factor in food safety and acceptability as microbiological criteria are used to assess the acceptability of food.  When a particular food is tested for a particular microorganism (toxin or metabolite) the results can indicate if:

  • Food is safe to eat or not.
  • Food is of acceptability quality.
  • Hygiene standards in the food establishment are satisfactory or unsatisfactory.

Microbiological risk assessment (MRA) is an emerging tool for the evaluation of the safety of food and water. World Health Organization suggests that microbiological risk assessment should be carried out so that appropriate remedial measures can be adopted to curtail the episodes of foodborne illness as a result of consumption of these foods.  Microorganisms commonly associated with foodborne illnesses include bacteria, viruses and parasites.

Contaminated food is a common source of human infections.


Among the groups of microorganism only bacteria, viruses and protozoa include the kinds of microorganisms that can make food unsafe. Generally, yeast and molds do not pose a biological hazard in food. Some molds produce hazardous toxins, but these toxins are considered chemical hazards.

Major microbiological hazards in food includes:

  • Bacterial hazards
  • Viral hazards
  • Parasitic hazards