The Genus Treponema
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The Genus Treponema STEVEN J. NORRIS, BRUCE J. PASTER, ANNETTE MOTER AND ULF B. GÖ BEL
Introduction and Habitats The genus Treponema (phylum Spirochaetes, order Spirochetales, family Spirochaetaceae) is composed of both pathogenic and nonpathogenic species indigenous to humans and animals. They are helical, tightly coiled, motile bacteria, ranging from 5–20 mm in length and 0.1–0.4 mm in diameter, and are best observed by dark-field microscopy (Fig. 1). The organisms stain poorly with the usual aniline dyes; however, those that are capable of aniline-dye uptake are Gramnegative. Staining can best be accomplished by the use of silver impregnation or immunofluorescent methods. The sequence of the genome of Treponema pallidum subsp. pallidum, the type species of the genus, was determined in 1998 (Fraser et al., 1998), and the sequence of the Treponema denticola genome is nearly completed. Information based on these genome sequences has been incorporated into sections of this chapter. Several topics covered in this chapter have been reviewed previously, including procedures for propagation of pathogenic treponemes in laboratory animals (Turner and Hollander, 1957; Miller, 1971), clinical aspects and diagnosis of treponemal infections (United States Public Health Service, 1968; Larsen, et al., 1998, 1999), the endemic treponematoses (Antal et al., 2002), the phylogeny of spirochetes (Paster and Dewhirst, 2000), T. pallidum pathogenesis and immunology (Norris, 1988a; Radolf, 1994; Blanco et al., 1997; Radolf et al., 1999), and the biology and in vitro culture of T. pallidum (Cox, 1994; Norris et al., 2001). In addition, a book focused on current topics in spirochete biology was published in 2001 (Saier and Garcia-Lara, 2001). Portions of this chapter were modified from the previous version by Miller, Smibert, and Norris (Miller et al., 1990). The reader is referred to these previous reviews where they are applicable, and individual articles are cited where they are particularly pertinent. The known frank pathogens of the genus Treponema are virtually identical organisms that are
obligate parasites of humans or (in the case of one species) rabbits (Table 1). These organisms are morphologically indistinguishable and share extensive DNA homology and proteome similarity; in addition, they have not been cultured continuously in vitro. The four human pathogens and the diseases they cause are: Treponema pallidum subsp. pallidum (syphilis), Treponema pallidum subsp. pertenue (yaws), Treponema pallidum subsp. endemicum (nonvenereal endemic syphilis), and Treponema carateum (pinta). The reclassification of T. pertenue and T. endemicum as subspecies of T. pallidum (Smibert, 1984a) is supported by >95% DNA homology by hybridization (Fieldsteel, 1983) and the virtual identity of known sequences from this group of organisms. Treponema carateum cannot be propagated in small laboratory animals or in culture and is still classified separately owing to the lack of genetic information. Treponema paraluiscunicu
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