Microorganisms can cause a variety of effects in food products including spoilage which primarily affects product quality, and food poisoning, which is generally caused by pathogens, .

Bacteria can enter food products through different routes. In food processing, foodborne microbes can be introduced from infected humans who handle the food, or by cross contamination from some other raw material and/or the in-plant environment. For example, bacteria and viruses can be introduced by the unwashed hands of food handlers who are themselves infected.

Culture media for Processed Food Industry

Product that is fully cooked can become cross contaminated if it comes into contact with raw material containing pathogens or with food contact surfaces that are contaminated.

In the kitchen, microbes can be transferred from one food to another by using the same knife, cutting board or other utensil to prepare both without washing the surface or utensil in between.

The way that food is handled after it is contaminated can also make a difference in whether or not an outbreak occurs.