The Genus Capnocytophaga
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The Genus Capnocytophaga E. R. LEADBETTER
Introduction/Habitat Bacteria included in the genus Capnocytophaga typically are aerotolerant anaerobes with a requirement for significant quantities of carbon dioxide (CO2) for initiation of growth—aerobic as well as anaerobic—and with the ability to form thin, spreading colonies (i.e., exhibit surface translocation) on solid media. They are common inhabitants of dental plaque in the oral cavities of mammals, from which they can be isolated in instances of periodontal diseases as well as from healthy individuals (Paster et al., 2001); they are less frequently isolated from lesions resulting from dog and cat bites and from inadvertant oral microbial contamination of open wounds (e.g., Chadha and Brady, 1999; Alexandrakis et al., 2000; Phibbs et al., 2002). Seven species of the genus are presently recognized (C. ochracea, gingivalis, sputigena, canimorsus, cynodegmi, hemolytica and granulosa) on the basis of several polyphasic analyses including phenotypic trait analysis, 16S rRNA analysis, DNA-DNA hybridization, fatty acyl composition of cell lipids and cellular protein profiles (Williams and Hammond, 1979a; Vandamme et al., 1996). Shortly after the initial characterization of isolates and grouping into three species (C. ochracea—the type strain, C. gingivalis and C. sputigena; Leadbetter et al., 1979), it was noted that strains otherwise uncategorized (known as “dysgonic fermenters,” e.g., group DF-1 of the United States Centers for Disease Control and Prevention [CDC]) should properly be considered Capnocytophaga (Williams et al., 1979b). Several DF-2 and DF-2-like isolates came to be considered identical to strains isolated from the mouths of dogs and were termed “C. canimorsus” and “C. cynodegmi” (Brenner et al. 1989), even though these latter species (unlike the type strain and other species) possessed catalase and oxidase activities. The properties of the Gram-negative fusiform cells in CDC group DF3 resemble but are not identical to those of DF1 and DF-2; these strains are not presently con-
sidered capnocytophagas (Vandamme et al., 1996). Human oral cavity isolates labeled originally Sphaerocytophaga (Graf, 1961; Graf, 1962) and Bacteroides oralis var. elongatus (Loesche et al., 1964) were so regarded probably because their traits were incompletely described, unrecognized, or of mistaken significance; such strains are now regarded as Capnocytophaga. Their DNA G+C content is 36–44 mol%. As revealed by phylogenetic analyses of 16S rRNA, the seven species are quite closely related (see Bernadet et al., 2002) and constitute a cohesive subgroup of the proposed family Flavobacteriaceae. As originally noted (Holt et al., 1979b), Capnocytophaga cells are judged Gram-negative both from actual staining results and from transmission electron microscopic analysis of the cell envelope. Surface appendages such as flagella or pili have not been observed, nor have significant intracellular inclusions regularly been reported. The slender rods (ca
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