Spirochetes, category of corkscrew-shaped bacteria. Bacteria are simple, unicellular organisms that are classified in the kingdom Monera (also called kingdom Prokaryotae). They have prokaryote cells, which means that they lack a nuclear membrane and other complex features. Spirochete bacteria are members of the order Spirochaetales. They move by means of two or more axial filaments, which are bundles of fibers that spiral around the cell body. Spirochetes show no evidence of any sexual life cycle and reproduce asexually by transverse fission, in which the organism divides in two across its width. Spirochetes may be free-living, commensal, pathogenic, or parasitic. The order includes two families, Spirochaetaceae and Treponemataceae.

Nonpathogenic Spirochetes

Members of the Spirochaetaceae family have

Members of the Spirochaetaceae family have cells with a definite protoplasmic structure and are largely saprophytic, living on dead or decaying organic matter; or free-living, inhabiting water, sewage, and other moist environments. Representatives of the genus "Spirochaeta", which are found in stagnant waters, are fairly long, ranging from 200 to 500 microns in length (1 micron = 0.000001 meter0.00004 in). Their protoplasm contains vacuoles and deep-staining granules. Members of the free-living genus "Saprospira", which are found in fresh and salt waters and in oysters, are also fairly long, ranging up to 100 microns in length. They have rigid, undulating coils and lack crista, or ridges. Such ridges are characteristic of another spirochete genus, "Cristispira", which is found in certain mollusks. "Cristispira" range from 45 to 100 microns in length and are cylindrical, with short inner segments and coarse spirals.

Pathogenic Spirochetes

Most of the family Treponemataceae are

Most of the family Treponemataceae are parasitic, and many of them are pathogenic (cause disease) in humans or animals. The family includes three genera: "Borrelia", "Treponema", and "Leptospira".

"Borrelia" have the shape of delicate

"Borrelia" have the shape of delicate, spiral filaments, 10 to 20 microns in length, with fairly regular coils. They can be cultivated in a laboratory and stain readily with aniline dyes but are best seen under a dark-field microscope. Some "Borrelia" species are saprophytic and apparently harmless. "Borrelia" "vincenti", together with a fusiform bacillus, " Fusobacterium dentium", is responsible for the ulcerative disease of the mouth known as Vincent`s gingivitis or trench mouth. Several species of "Borrelia" are transmitted through the bites of body lice and ticks and cause relapsing fever, in which the patient suffers repeated bouts of fever and chills. In 1983 the spirochete "Borrelia burgdorferi" was identified as the causative agent of Lyme disease, which is transmitted by deer ticks.

By far the most dreaded genus of spirochetes

By far the most dreaded genus of spirochetes is "Treponema", a strictly anaerobic and parasitic form, which is difficult to stain and to culture. "Treponema" "pallidum" is the causative agent of syphilis. It is a delicate, spiral organism, 5 to 15 microns in length, and is highly flexible and motile. It is best seen under a dark-field microscope. "Treponema" "pertenue", which is indistinguishable from "Treponema" "pallidum", causes the tropical skin disease, yaws. Some other "Treponema" species are pathogenic for humans and animals.

The genus "Leptospira" is represented

The genus "Leptospira" is represented by small, slender organisms, which are six to nine microns long, with fine, closely wound coils that are often hooked at both ends. It is aerobic and can be grown in laboratory cultures. "Leptospira" "interrogans" causes leptospirosis, an infectious disease that primarily affects the liver and kidneys. Leptospirosis is spread through contact with infected urine or water and can affect both humans and animals. Sometimes dogs may be infected with the spirochete but can be immunized against leptospirosis. A severe form of leptospirosis in humans is called Weil`s disease.

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