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MICROORGANISMS

De Kruif, Paul. Microbe Hunters. New York: Pocket Books, 1964.

Harrigan, Wilkie F. Laboratory Methods in Food Microbiology. 3d

ed. London: Harcourt Brace, 1998.

Lechevalier, Hubert A., and Morris Solotorovsky. Three Cen- turies of Microbiology. New York: McGraw-Hill, 1965.

Mortimore, Sara, and Carol Wallace. HACCP: A Practical Ap- proach. 2d ed. Gaithersburg, Md.: Aspen, 1998.

Postgate, John. Microbes and Man. 3d ed. Cambridge: Cam- bridge University Press, 1992.

Reed, Gerald, ed. Prescott and Dunn’s Industrial Microbiology. 4th

ed. Westport, Conn.: AVI Publishing, 1982.

Stanier, Roger Y., John L. Ingraham, Mark L. Wheelis, and Page R. Painter. The Microbial World. 5th ed. Englewood Cliffs, N.J.: Prentice-Hall, 1990.

U.S. Food and Drug Administration, Center for Food Safety

and Applied Nutrition, Bacteriological Analytical Manual

Online. Available at http:/vm.cfsan.fda.gov/ebam/bam-toc .html.

U.S. Food and Drug Administration, Center for Food Safety

and Applied Nutrition, Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. Available at http://vm.cfsan

.fda.gov/mow/badbug.zip.

Vanderzant, C., and D. Splittstoesser, eds. Compendium of Meth-

ods for the Microbiological Examination of Foods. Washington,

D.C.: American Public Health Association, 1992.

Wood, Brian J. B., ed. Microbiology of Fermented Foods. 2d ed., 2 vols. London: Blackie Academic and Professional, Thom- son Science, 1998.

Susan Rodriguez Roy Thornton

MICRONESIA. See Pacific Ocean Societies.

MICROORGANISMS. Microorganisms are organ- isms (forms of life) requiring magnification to see and re- solve their structures. “Microorganism” is a general term that becomes more understandable if it is divided into its principal types—bacteria, yeasts, molds, protozoa, algae, and rickettsia—predominantly unicellular microbes. Viruses are also included, although they cannot live or reproduce on their own. They are particles, not cells; they consist of deoxyribonucleic acid (DNA) or ribonucleic acid (RNA), but not both. Viruses invade living cells— bacteria, algae, fungi, protozoa, plants, and animals (in- cluding humans)—and use their hosts’ metabolic and genetic machinery to produce thousands of new virus par- ticles. Some viruses can transform normal cells to cancer cells. Rickettsias and chlamydiae are very small cells that can grow and multiply only inside other living cells. Al- though bacteria, actinomycetes, yeasts, and molds are cells that must be magnified in order to see them, when cultured on solid media that allow their growth and mul- tiplication, they form visible colonies consisting of mil- lions of cells.

ENCYCLOPEDIA OF FOOD AND CULTURE

Many people think of microorganisms mainly in terms of “germs” causing diseases, but some “germs” are beneficial to humans and the environment. Disease- causing (pathogenic) microorganisms need to be con- trolled, and in many cases, beneficial microorganisms are also controlled in plant and food production.

For thousands of years, people had no concept or knowledge of organisms invisible to the naked eye. In fact, it is only within the last several hundred years that magnification systems (lenses, magnifiers, microscopes) were developed that enabled scientists to observe mi- croorganisms. In 1673 Antoni van Leeuwenhoek, a linen merchant in Delft in the Netherlands, was the first to ob- serve and study microorganisms, using single lenses that magnified objects fifty to three hundred times. The role played by microorganisms was not clarified until the 1830s, when Theodor Schwann in Germany demon- strated that yeasts were responsible for alcohol produc- tion in beer and wine fermentations.

In 1854, Louis Pasteur in France found that spoilage of wines was due to microorganisms (bacteria) that convert sugars to lactic acid, rather than the alcohol pro- duced by yeasts. He developed the process of “pasteur- ization,” in which the temperature of food materials is raised to about 140 to 158°F (60 to 70°C), thereby killing many spoilage organisms. Pasteur also discovered that certain bacteria are responsible for the souring of milk. Today, milk is generally pasteurized to reduce its con- tent of microorganisms, to extend its keeping quality, and to protect against pathogenic microorganisms that may be present.

Pasteur also discovered that each type of fermenta- tion, as defined by the end products, is caused by specific microorganisms and requires certain conditions of acid- ity or alkalinity. He discovered further that some mi- croorganisms, the aerobes, require oxygen and others, the anaerobes, grow only in the absence of oxygen. The lat- ter probably developed in the earliest days of the earth when there was no oxygen in the atmosphere.

Microorganisms are present in high populations in soil, and in varying numbers in the air we breathe, the water we drink, and the food we eat; they are on our skin and in our noses, throats, mouths, intestinal tracts, and other bodily cavities. They are everywhere in our envi- ronment.

Evolution of Microorganisms

Microorganisms came into being on earth over a period of about 1.2 to 1.5 billion years. Fossil microbes have been found in rocks 3.3 to 3.5 billion years old. Since then, microorganisms have had the principal task of re- cycling organic matter in the environment. As such they are absolutely essential to the health of the earth. With- out them, the earth would be a gigantic, permanent waste dump.

Microorganisms are responsible for recycling the huge masses of organic matter synthesized by plants as

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