IDENTIFICATION AND PARTIAL CHARACTERIZATION OF A GROUP OF WEAKLY BETA-HEMOLYTIC INTESTINAL SPIROCHETES OF SWINE DISTINCT FROM SERPULINA-INNOCENS ISOLATE B256

Comparative analyses of a group of 16 weakly beta-hemolytic spirochete s isolated from feces and mucosal scrapings of intestines of swine in the midwestern United States, and eastern Canada revealed the existenc e of a phenotypically and genotypically related group of 7 isolates. A lthough isolates in this group differed from all known reference isola tes of intestinal spirochetes of swine, partial similarity was detecte d with S. joneseae isolate 16, a newly identified weakly beta-hemolyti c intestinal spirochete of human beings. In addition to producing weak beta-hemolysis on blood agar plates, S. innocens isolates B256 and 4/ 71, S.joneseae isolate 16, and the 16 field isolates lacked the charac teristic ring phenomenon described for Serpulina hyodysenteriae, an en teropathogenic spirochete of swine. All but one of the field isolates of weakly beta-hemolytic intestinal spirochetes gave negative results for indole production. The same isolates yielded variable results for alpha-galactosidase production. By transmission electron microscopic e xamination of negatively-stained cross-sections of spirochetes, the is olates segregated into groups containing either 4 to 7 or 9 to 16 prof iles of axial filaments per cell cross-section. Analyses of genomic DN A of selected isolates using whole-genome cross-hybridization revealed a single genetic type consisting of 7 field isolates of weakly beta-h emolytic intestinal spirochetes. The 7 field isolates were distinct fr om the reference isolates S innocens isolates B256 and 4/71, S. hyodys enteriae isolates B78 and B204, and Treponema succinifaciens isolate 6 091 based on the number of axial filaments per cell cross-section and lack of cross-hybridization signal. S. joneseae isolate 16, had the sa me number of axial filaments per cell cross-section and produced a wea k hybridization signal with a representative isolate of the 7 weakly b eta-hemolytic field isolates from swine. This report suggests the exis tence of a widely distributed group of closely related weakly beta-hem olytic intestinal spirochetes of swine with genotypic characteristics distinct from S. innocens isolate B256.