Identification and partial characterization of a group of weakly β-hemolytic intestinal spirochetes of swine distinct from Serpulina innocens isolate B256

Comparative analyses of a group of 16 weakly β-hemolytic spirochetes isolated from feces and mucosal scrapings of intestines of swine in the midwestern United States, and eastern Canada revealed the existence of a phenotypically and genotypically related group of 7 isolates. Although isolates in this group differed from all known reference isolates of intestinal spirochetes of swine, partial similarity was detected with S. joneseae isolate 16, a newly identified weakly β-hemolytic intestinal spirochete of human beings. In addition to producing weak β-hemolysis on blood agar plates, S. innocens isolates B256 and 4 71 , S. joneseae isolate 16, and the 16 field isolates lacked the characteristic ring phenomenon described for Serpulina hyodysenteriae, an enteropathogenic spirochete of swine. All but one of the field isolates of weakly β-hemolytic intestinal spirochetes gave negative results for indole production. The same isolates yielded variable results for α-galactosidase production. By transmission electron microscopic examination of negatively-stained cross-sections of spirochetes, the isolates segregated into groups containing either 4 to 7 or 9 to 16 profiles of axial filaments per cell cross-section. Analyses of genomic DNA of selected isolates using whole-genome cross-hybridization revealed a single genetic type consisting of 7 field isolates of weakly β-hemolytic intestinal spirochetes. The 7 field isolates were distinct from the reference isolates S. innocens isolates B256 and 4 71 , S. hyodysenteriae isolates B78 and B204, and Treponema succinifaciens isolate 6091 based on the number of axial filaments per cell cross-section and lack of cross-hybridization signal. S. joneseae isolate 16, had the same number of axial filaments per cell cross-section and produced a weak hybridization signal with a representative isolate of the 7 weakly β-hemolytic field isolates from swine. This report suggests the existence of a widely distributed group of closely related weakly β-hemolytic intestinal spirochetes of swine with genotypic characteristics distinct from S. innocens isolate B256.