The Genus Porphyromonas
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The Genus Porphyromonas FRANK C. GIBSON AND CAROLINE ATTARDO GENCO
Introduction Members of the genus Porphyromonas are characterized by the production of porphyrin pigments. The genus Porphyromonas was recognized as a separate taxon on the basis of ribosomal RNA homology and 16S rRNA data (Olsen et al., 1999). The most extensively characterized species of the genus is Porphyromonas gingivalis (a Gram-negative anaerobe), which has been long considered an important pathogen associated with human periodontal disease. Periodontal diseases comprise a group of inflammatory diseases of the gingiva and supporting structures of the periodontium. They (the most common of the destructive oral inflammatory diseases) are characterized by the bacterially initiated conversion of a healthy gingival region to one that is inflamed (gingivitis) and by the destruction of the supporting structures of the teeth (periodontitis). While a large number of different bacterial species exist in the periodontal environment, it is now recognized that the large number of bacteria (bacterial load) per se does not result in the biological progression from health to periodontal disease. Rather the establishment and growth of a very few of the more than 300 proposed different bacterial species resident in the subgingival niche are apparently periodontopathic (Holt et al., 2000), and these include Fusobacterium nucleatum, Bacteroides forsythus, Prevotella intermedia, Treponema denticola and P. gingivalis. Porphyromonas gingivalis is essentially absent during periodontal health, but during disease progression to periodontitis, can reach a very significant percentage of the pathogenic microbiota. Eradication of P. gingivalis from the subgingival microbial population correlates with resolution of the disease (Moritz et al., 1998).
Description of the Genus The twelve species of the genus Porphyromonas have been isolated from the oral cavities of humans, dogs, cats, and nonhuman primates.
More than likely, members of the genus are also associated with a large number of other warmblooded animals. These organisms were originally classified in the genus Bacteroides, which is phylogenetically closely related (Fig. 1). Members of the genus are obligatorily anaerobic, nonsporeforming, nonmotile rods (0.5–0.8 by 1.0–3.5 mm; Table 1). They have also been described as cocco-bacilli depending on their stage of growth when they are examined. Characteristic of the genus is the production of large amounts of cell-associated protoheme. The major fermentation end products of growth on complex carbohydrates (except in the case of asaccharolytic P. gingivalis) and proteins are n-butyrate, propionate and acetate. These endproducts account for much of the malodor associated with oral infections. Small amounts of isovalerate, isobutyrate, succinate and phenylacetate are also produced. While several of the strains (i.e., P. gingivalis and P. macacae) possess significant proteolytic activity, the other strains are relatively nonproteolytic. Por
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