The Genus Brachyspira
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The Genus Brachyspira THADDEUS B. STANTON
Phylogeny and Taxonomy Brachyspira is the sole genus assigned to the proposed Family “Brachyspiraceae” in the Order Spirochaetales (Paster and Dewhirst, 2000). The Order Spirochaetales contains all spirochetes. The spirochetes represent a monophyletic lineage and a major early branch in eubacterial evolution (Paster et al., 1984; Paster and Dewhirst, 2000). Brachyspira cells share with other spirochetes several properties that distinguish them from other bacteria. These include a helical cell shape (Fig. 1) and a cell ultrastructure that features internal periplasmic flagella, 16S rDNA sequences with spirochete signature nucleotide bases, and a natural resistance to the antibiotic rifampin (Paster and Dewhirst, 1997; Paster and Dewhirst, 2000). Brachyspira species are readily differentiated from other spirochete genera based on comparisons of their 16S rDNA sequences (Paster et al., 1991; Paster and Dewhirst, 1997).
General Characteristics Brachyspira species have been isolated from animal or human intestinal contents, fecescontaminated habitats (e.g., duck ponds), and human blood. They are anaerobic bacteria but are aerotolerant due, at least in part, to high NADH oxidase activity. They use soluble sugars as carbon and energy sources. Growing cells of Brachyspira species (B. aalborgi has not been investigated) consume low concentrations of oxygen via NADH oxidase and produce acetate, butyrate, H2 and CO2 from glucose. Some species also produce ethanol. Brachyspira DNAs have a low G+C content (24.5–26.7 mol%; undetermined for B. aalborgi). Brachyspira species have high 16S rDNA sequence similarities with each other. Brachyspira strains have been assigned to eight electrophoretic type (ET) groups based on multilocus enzyme electrophoresis (MEE) analysis. The MEE groups correspond to seven species as defined from DNA homology studies and one currently uncharacterized provisional species (“B. canis”). Uncharacterized intestinal spi-
rochetes of chickens are likely to represent a new Brachyspira species, “B. pulli” (Gabe et al., 1998; Stephens and Hampson, 2001). It has been recommended that uncharacterized/uncultured spirochetes from the human intestine be named “B. christiani” (Jensen et al., 2001).1
Brachyspira Species There are seven recognized species of the genus Brachyspira (Table 1). The species B. hyodysenteriae, B. pilosicoli, B. alvinipulli and B. intermedia have been shown to cause disease when inoculated as pure cultures into their healthy, natural hosts. The type strain of each species is available from the American Type Culture Collection (ATCC; Table 1) and these strains should be included in studies of Brachyspira species.
History of Brachyspira Taxonomy In the past 25 years, there have been several taxonomic changes for spirochetes now assigned to the genus Brachyspira. Initially, the designation “Treponema hyodysenteriae” was applied to both pathogenic (strongly hemolytic) and nonpathogenic (weakly hemolytic) strains of
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