Phenotypic, genotypic, and antimicrobial characteristics of Streptococcus halichoeri isolated from humans and proposal to rename Streptococcus halichoeri as Streptococcus halichoeri subsp. halichoeri and description of Streptococcus halichoeri subsp. hominis subsp. nov., a bacterium associated with human clinical infections.

Shewmaker PL1, Whitney AM2, Humrighouse BW2.

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Abstract

Phenotypic, genotypic and antimicrobial characteristics of six phenotypically distinct human clinical isolates that most closely resembled the type strain of Streptococcus halichoeri isolated from a seal are presented. Sequencing of the 16S rRNA, rpoB, sodA and recN genes, comparative whole genome analysis, conventional biochemical and rapid ID 32 STREP identification methods, and antimicrobial susceptibility testing were performed on the human isolates, the type strain of S. halichoeri, and type strains of closely related species. The six human clinical isolates were biochemically indistinguishable from each other and showed 100% 16S rRNA, rpoB, sodA and recN gene sequence similarity. Comparative 16S rRNA gene sequencing analysis revealed 98.6% similarity to S. halichoeri CCUG 48324T, 97.9% to S. canis ATCC 43496T and 97.8% to S. ictaluri ATCC BAA-1300T. A 3530 bp fragment of the rpoB gene was 98.8% similar to S. halichoeriT, 84.6% to S. canisT and 83.8% to S. ictaluriT. S. halichoeriT and the human clinical isolates were susceptible to the antimicrobials tested based on CLSI guidelines for Streptococcus species viridans group with the exception of tetracycline and erythromycin. The human isolates were phenotypically distinct from the type strain isolated from a seal; comparative whole genome sequence analysis confirmed that the human isolates were S. halichoeri. On the basis of these results, a novel subspecies, Streptococcus halichoeri subsp. hominis is proposed for the human isolates and S. halichoeri subsp. halichoeri for the grey seal isolates. The type strain of the novel subspecies is SS1844T = CCUG 67100T = LMG 28801T.