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U.S. Department of Health and Human Services


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List of Terms: B

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   Did You Know?  Photo of Anton van Leeuwenhoek
Anton van


Anton van Leeuwenhoek used his development of good-quality microscopes to discover bacteria in 1674.




A single bacterium can grow to millions in 10 to 12 hours! See photo of a bacterium multiplying below.
 Photo of a bacterium multiplying
Photo: James A. Sullivan/Cells Alive


>Bacteria (plural) or Bacterium (singular)
Single-cell, independently-replicating microorganisms that lack a membrane-bound nucleus and other organelles.

Food Safety Implication: Most bacteria are harmless and can even be beneficial, such as those used to make yogurt. However, harmful bacteria can cause foodborne illness in humans. In fact, out of all the micro-organisms of concern for food safety, bacteria pose the greatest threat to human health. Food can become contaminated with foodborne bacteria mainly from:

  • Animals - manure or saliva, or disease microorganisms within the animals. For example, if meat contains harmful bacteria, and it is not thoroughly cooked to kill the bacteria, foodborne illness may result once the food is eaten.
  • Soil - contaminated by animal droppings, which can be transferred to the crops that we eat and also by normal soil residents.
  • Water - contaminated by animal droppings, which can be transferred to humans when the water is consumed or sprayed on crops.
  • Humans - from infected hands that touch the food we eat.

Where They Live: Bacteria are found everywhere. They live on and in the human body. For example, about 600 types of bacteria live on the skin, and saliva contains about 6 different kinds of bacteria. Water, wind, insects, plants, and animals can carry bacteria. They also live on clothes, human hair, room-temperature foods, and surfaces in our homes, schools, and workplaces.

How They Grow: Most bacteria multiply through a process called binary fission, a form of asexual reproduction in which the deoxyribonucleic acid (DNA) that holds all of the cell's genetic information doubles, the cell splits, and two independent cells are formed. One cell can double within 20 to 30 minutes.

You can't see, taste, or smell bacteria in food, but they can be present in food and multiply rapidly under the right conditions. That's why it's important to properly handle all foods.

To Survive and Reproduce, Bacteria Need:

  • Nutrients - Bacteria need many of the same nutrients as humans in order to thrive, such as glucose, amino acids, and some vitamins and minerals. For example, bacteria grow rapidly in high-protein foods, such as meat, poultry, eggs, dairy, and seafood.
  • Moisture - Most bacteria thrive in moist environments. Dry foods, such as sugar, flour, dry cereal, rice, cookies, and biscuits do not have enough moisture to allow bacteria to grow. On the other hand, 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.
  • pH - Most bacteria will not grow at pH levels below 4.6. Microorganisms thrive in a pH range above 4.6. That's why acidic foods like vinegar and fresh fruits (especially citrus) seldom provide a favorable climate for pathogenic bacteria. (Also see pH.)
  • Temperature - Bacteria can multiply at temperatures between about 33.34° F (1° C) and 125° F (52° C). They divide rapidly at 80° to 105° F (27° to 41° C). Proper cooking kills bacteria in food and chilling foods slows the growth of bacteria. Both methods decrease the risk of foodborne illness.
  • Time - Bacteria can double their numbers in 20 minutes under optimal conditions. Foodborne pathogenic bacteria grow best at human body temperature (98.6° F, 37° C) and can divide 2 to 3 times per hour. Food that's left out at room temperature for long periods of time creates an inviting environment for bacterial growth.

How to Control Bacteria in Foods: One way is to keep cold food cold, meaning below the temperature where bacteria can grow. Usually, this is below 40° F (4° C), but some pathogenic bacteria can grow slowly at 32° F (0° C), the temperature at which water freezes.

Good Bacteria: Most bacteria are beneficial to us in our everyday lives, both inside our bodies and in other applications. Here are some examples of good bacteria:

  • E. coli (not the O157:H7 variety) plays an important role in our digestive system. It is present in the human small intestine. E. coli helps create vitamin K in the body and aids in digestion.
  • Streptomyces is soil bacteria used to make Streptomycin, an antibiotic used to treat infections.
  • Lactobacillus acidophilus turns milk into yogurt.

FAQSome people say that alcohol or vinegar can kill bacteria. Is this true?

Yes, ethanol and isopropyl alcohol and vinegar, which is an acetic acid, do kill bacteria.

Ethanol alcohol at 70% is more effective at killing bacteria than at 90 to 100% because the alcohol gets inside the cell better. Isopropyl alcohol is even more effective at killing bacteria because it is less volatile. While alcohol is a good disinfectant for inactivating many bacteria, it will not inactivate bacterial spores that are resistant. At acidic pH levels, many bacteria are inactivated by vinegar (acetic acid).

Bacteria also assist with the production of certain foods such as cheese, buttermilk, sauerkraut, vinegar, and pickles. In certain crop plants like legumes, bacteria can take nitrogen from the air to the roots and change it into ammonia, which is one of several important compounds required for healthy plant growth.

Bacteria also play a role in recycling. They have the ability to decompose waste in the environment by breaking it down into nutrients that are useful to soil (also known as composting).

Harmful Bacteria: Pathogenic bacteria - those that are harmful - cause disease. They have the ability to cause disease by invading human tissue or producing toxic substances that can alter normal body functions. (See Pathogen for a list of the 12 Most Unwanted Bacteria that cause foodborne illness.)

Diseases Caused by Pathogenic Bacteria Include: Foodborne illness, tuberculosis, cholera, bacterial meningitis, Legionnaire's disease, rheumatic fever, typhoid, tetanus, pneumonia, strep throat, stomach ulcers, tooth decay, and skin infections.

Three distinct bacteria shapes: cocci (round), bacilli (rod-shaped), or spirilla (spiral).

Bacteria typically have one of three distinct shapes: cocci (round), bacilli (rod-shaped), or spirilla (spiral). Bacterial cells differ from other cells in that they do not have a well-defined nucleus enclosing their genetic material. Instead, bacteria have a nucleoid, which is a circular loop of double-stranded helical DNA that carries the genes.


> Bacteriophage (also known as Bacterial Virus or Phage)
Any group of viruses that infect bacteria.

How It Works: Thousands of varieties of phage exist, each of which may infect only one type or a few types of bacteria. During infection, a phage attaches to a bacterium and injects its genetic material into the cell. The phage takes over the metabolic machinery of the bacteria and produces new phage particles, which cause the bacteria to lyse (break open). This process releases many new phage, which seek out other bacteria to invade and repeat the cycle.

Phage Uses: Soon after making their independent discoveries of phages in the early 1900s, scientists Frederick Twort and Felix d'Herelle tried to use phages in treating human bacterial diseases, such as the bubonic plague and cholera. However, phage therapy was not successful. After the discovery of antibiotics in the 1940s, phage therapy was virtually abandoned. But with the rise of drug-resistant bacteria in the 1990s, the therapeutic potential of phages is receiving renewed attention.

>"Best If Used By" Date
A calendar date on the packaging of a food product, which represents the recommended time limit a food should be used within for best flavor or quality. It is not a purchase or safety date. (Also see Expiration, "Sell By," and "Use By" Dates.)


>Binary Fission (see Bacteria)


> Binomial Nomenclature
The naming system for bacteria, which allows scientists to carefully name any newly found bacterium so that it won't be confused with known bacteria. (Also see Genus and Species.)

In binomial nomenclature, the names of bacteria have a first (the genus) and last (species) name. For example for the bacterium, Escherichia coli, Escherichia is the genus and coli is the species. The first letter of genera (plural of genus) names are always capitalized, while species names receive a lower-case first letter. Since names are always in Latin, the names are italicized, like all foreign terms.

>Biotechnology (also known as Food Engineering or Genetic Engineering)
The techniques used by scientists to modify deoxyribonucleic acid (DNA) or the genetic material of a bacterium, plant, or animal in order to achieve a desired trait.

Food Safety Implication: Biotechnology is used to improve the quality and quantity of food.

How It Works: To change a plant's traits, scientists use a gun-like instrument to insert 1, 2, or 3 genes into the plant to give it new, advantageous characteristics. For animal production, scientists can select the traits they want and "genetically engineer" or introduce those genes into the animals.

Some Advantages of Biotechnology:

  • Increases harvest yields of food.
  • Improves the taste, nutrition, texture, size, or color of produce. For example, biotechnology can cause a tomato to stay on the vine longer, which helps it develop more flavor and a brighter color.
  • Lengthens the season of fruits and vegetables and helps cows produce more milk.
  • Allows plants to absorb more nutrients from the soil, thus decreasing the need for fertilizers.
  • Increases the ability of plants to resist pests and disease.