Bacteria, molds, parasites, and viruses are types of microorganisms that can cause food spoilage and/or food-borne illnesses. The food substrates each of these types prefers vary from one to another. Consequently, the care of food during storage and preparation varies with the type of food and its likely contaminants.

Bacteria are the type of microorganism most commonly causing food-borne illnesses. These microscopic organisms are single-celled and vary in shape, being possibly filament-like, rod-shaped, round, or spiral. When live bacterial cells are consumed, they may create symptoms ranging from general discomfort to nausea, vomiting, and even death. Although many bacteria grow well in a wide range of foods, sugar and salt concentrations that create an unfavorable osmotic pressure can destroy bacteria by dehydration.

Classification of bacteria may be done on the basis of adaptability to oxygen requirements or temperature levels. On The Former Basis, bacteria are aerobic or anaerobic, depending  on their need for oxygen for survival. Aerobic bacteria will die if they lack an adequate supply of oxygen.

Conversely, anaerobic bacteria flourish in an oxygen-free system. Bacteria That Are Able to reproduce  rapidly at temperatures well above room temperature are classified as    thermophilic (heat loving), and those thriving at cold temperatures are cryophilic (cold loving). Clearly, there are some bacteria capable of adapting to many of the conditions employed in storing foods.

Molds are usually multicellular  and often form a filament  topped by a head with spores that scatter when food containing a colony of mold is moved.

Molds can be seen sometimes on cheeses and some other foods, such as loaves of breads made without preservatives and stored at room temperature. The moisture level maintained in a tightly wrapped loaf of bread is just right for molds to flourish. However, molds can remain viable even if a food has been stored at moisture levels also was 13 percent, a characteristic that makes molds the most troublesome of the microorganisms to control in the storage of dried foods.

The visibility of molds on foods helps to avoid the problem of food poisoning from them. However, a few molds produce  mycotoxins that are poisonous. Perhaps the most familiar example is aflatoxin, mycotoxin sometimes found in stored moldy peanuts, a problem particularly in some parts of Africa.

Viruses that can be food- and water-borne are rather small, spherical viruses that contain single-strand DNA (deoxyribonucleic acid) or RNA (ribonucleic acid). The two that have been particularly  prominent problems in foods are hepatitis A and noroviruses.  The virus  particle is inactive in a food until ingested by a receptive host.

Replication of the virus occurs in the host’s cells, not in the  food, but viruses can survive in foods for very long times. Contamination of food by these viruses can be from fecal origin or from vomit. Control of viral food-borne illness requires elimination of any possible contamination from fecal matter or vomit.

Professional Cooking OSC Microbio 01 03 Sizes

The relative sizes of various microscopic and Nonmicroscopic objects. Note that a typical virus measures about 100 nm, 10 times smaller than a typical bacterium (~1 µm), which is at least 10 times smaller than a typical plant or animal cell (~10–100 µm). An object must measure about 100 µm to be visible without a microscope.

How big is a bacterium or a virus compared to other objects? Check out this
interactive website to get a feel for the scale of different microorganisms.


Examples of potential food hazards during production have received worldwide press coverage and generated considerable efforts to minimize identified risks in the future. For example, mad cow disease (actually named bovine spongiform encephalopathy, or BSE), a fatal disease in cattle, has been linked to new variant  Creutzfeldt–Jakob disease (CJD) in humans. This is classified as a  prion disease; a prion is an abnormal agent characterized by abnormal folding of prion proteins in the brain and if transmitted results in a fatal condition in the host  Outbreaks of mad cow disease have resulted in huge economic losses to cattle farmers in Britain and several other countries.


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Infected herds had to be destroyed in 1986 and subsequent years to prevent continuing spread of the disease to animals  throughout the world. The infection originally spread through the sale of animal feed containing animal tissue from infected sheep whose BSE did not produce immediate symptoms. International efforts are being made to prevent the spread of the disease by regulating the sources of cattle feed. The United States has been able to mostly avoid contamination by BSE due to a ban on feeding scrapie-infected tissue as far back as 1932 & the important ruminant feed restrict that has been in effect since 1997. Additionally, the United States has been proactive in putting up necessary firewalls to protect the U.S. food supply and its exports.

  • BACTERIA : Round red-shaped, or spiral single-celled microorganisms in soil, water, or organic matter.
  • AEROBIC: Requiring air for survival.
  • ANAEROBIC: Living without air.
  • THERMOPHILIC:   Thriving in warm temperatures.
  • CRYOPHILIC Cold loving
  • MOLDS Filamentous, often wooly fungi that can thrive on damp surfaces, such as cheeses.
  • MYCOTOXINS Toxic substances produced by some molds.
  • AFLATOXIN Mycotoxin   produced by molds (Aspergillus flavus or Aspergillus parasiticus) in some food crops, for  example, peanuts grown in mold-contaminated soil or stored in a damp place.
  • VIRUS Submicroscopic molecules composed of genetic material surrounded by a protein coat; some can cause diseases in their host.
  • MAD  COW DISEASE Fatal disease of the central    nervous system sometimes occurring in cows caused by eating feed containing infected meat and bone meal; another name for bovine spongiform encephalopathy  (BSE).
  • CREUTZFELDT–JAKOB DISEASE Fatal brain    disease in humans that can be contracted by eating beef from cattle with mad cow disease.
  • PRION Abnormal agent that is transmitted to cause a fatal condition    characterized by abnormal folding of prion proteins in the brain, as in BSE.


Photo by Chokniti Khongchum from Pexels
— Information on prion diseases, including BSE.
— FDA site for BSE information.



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