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U.S. Department of Health and Human Services


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List of Terms: M

Return to Comprehensive List of Terms


Did You Know?

Microorganisms cannot grow on dry foods due to the lack of moisture. Most bacteria thrive in moist environments. That’s why dry foods like cereals or spices can sit out at room temperature.
However, if dry foods become contaminated - from infected hands or equipment, for example - bacteria can survive on the food and make people ill, but they can’t grow or multiply until the food is eaten.
Microorganisms like yeast, for example, are sometimes intentionally added to foods to cause fermentation, and mold is a micro- organism that is used to make penicillin, a powerful antibiotic.


It's easier for mold to permeate soft foods like jellies and soft cheeses. Discard these types of food if you see any signs of mold — it can easily spread through the entire product. With hard foods like some cheeses, you can cut away the moldy areas. However, discard them if mold growth is extensive or the food has lost its original color and texture.


> Methylene Blue  
A basic thiazine dye commonly used as a biological stain and an oxidation-reduction indicator.


> Microorganism
A microscopic life form that cannot be seen with the naked eye. Types of microorganisms include: bacteria, viruses, protozoa, fungi, yeasts, and some parasites and algae.


> Mold
A fungus-type Microorganism whose growth on food is usually brightly colored and fuzzy.

Food Safety Implication: Molds grow well on most types of food. Certain molds produce a toxin under the surface of the food. Toxins can cause foodborne illness.

Food Safety Precautions:

  • Discard most moldy foods. You can sometimes save hard cheese, salamis, and firm fruits and vegetables by cutting the mold out, but if mold growth is extensive, throw the food away.
  • Never taste food that looks or smells strange to see if you can still use it. When in doubt, throw it out.
  • Uncovered foods that are left out of the refrigerator are exposed to mold spores in the air. To help prevent mold contamination, cover foods. Remember, don't leave any perishables out at room temperature for more than 2 hours.
  • Clean the inside of your refrigerator with hot, soapy water regularly and discard any moldy foods. Mold spores from infected food can build up in your refrigerator, thus shortening the life of other foods.
  • Refrigerate canned and vacuum-packed items after opening. Air that gets in after you break the seal can promote mold growth.
  • Keep those great mold spreaders, such as dishcloths, dishrags, sponges, and mops, clean and fresh. A musty smell means they're moldy. Launder them frequently in the hot cycle of your washing machine.

Microscopic Mold
Photo: Eugene C. Cole DrPH; Dyncorp Health Research Services
Microscopic Mold
Molds may grow on many foods, including
bread and acidic foods like jams, jellies, and canned foods.

How It Grows: Mold requires only minimal moisture and air to grow. For the first 2 to 3 days, most molds look white. The surface mold you see is just the tip of the iceberg. The latter part of the mold plant is made up of threads that invade the food below the surface. These "roots" nourish the mold plant. In those few molds that produce poisons, the mycotoxins are contained in and around these threads.

Molds prefer higher temperatures, however, some can also grow in the refrigerator. Molds also can survive in salt and sugar better than most other food invaders. So you may find mold in refrigerated jams and jellies (high sugar content) and in cured, salty meats like ham, bacon, and salami.

Beneficial Molds: Many molds perform useful functions, such as:

  • Age and flavor cheeses;
  • Help in making bread and preparing soy sauce;
  • Produce penicillin;
  • Manufacture citric acid, which is used to flavor soft drinks.

Harmful Molds: Many molds are harmful to us and can:

  • Hasten food spoilage;
  • Cause allergic and respiratory problems;
  • Produce mycotoxins or poisons under the right conditions. Very few molds have this capability.


> Mutation
An alteration in the hereditary material of a cell, which is transmitted to the cell's offspring. Mutations take place in the genes, which are made up of deoxyribonucleic acid molecules.

During bacterial reproduction, genes may mutate, and occasionally a mutation may develop more harmful bacteria or help the bacteria become resistant to a specific antibiotic.


> Mycotoxins
Naturally-occurring toxins produced by fungi (molds) in food and animal feed. Some examples include: aflatoxins, fumonisins, deoxynivalenol, and patulin.