Pangenomic analysis of Helcococcus ovis reveals widespread tetracycline resistance and a novel bacterial species, Helcococcus bovis.

Helcococcus ovis (H. ovis) is an opportunistic bacterial pathogen of a wide range of animal hosts including domestic ruminants, swine, avians, and humans. In this study, we sequenced the genomes of 35 Helcococcus sp. clinical isolates from the uterus of dairy cows and explored their antimicrobial resistance and biochemical phenotypes. Phylogenetic and average nucleotide identity analyses placed four Helcococcus isolates within a cryptic clade-representing an undescribed species, for which we propose the name Helcococcus bovis sp. nov. We applied whole genome comparative analyses to explore the pangenome, resistome, virulome, and taxonomic diversity of the remaining 31 H. ovis isolates. H. ovis was more often isolated from cows with metritis, however, there was no associations between H. ovis gene clusters and uterine infection. The phylogenetic distribution of high-virulence determinants of H. ovis is consistent with convergent gene loss in the species. The majority of H. ovis strains (30/31) contain mobile tetracycline resistance genes, leading to higher minimum inhibitory concentrations of tetracyclines in vitro. In summary, this study showed that the presence of H. ovis is associated with uterine infection in dairy cows, that mobile genetic element-mediated tetracycline resistance is widespread in H. ovis, and that there is evidence of co-occurring virulence factors across clades suggesting convergent gene loss in the species. Finally, we introduced a novel Helcococcus species closely related to H. ovis, called H. bovis sp. nov. HighlightsO_LIThe presence of Helcococcus ovis is associated with uterine infection in dairy cows C_LIO_LIMobile genetic element-mediated tetracycline resistance is widespread in H. ovis C_LIO_LICo-occurring virulence factors across clades suggest convergent gene loss in the species C_LIO_LIHelcococcus bovis is a novel species closely related to Helcococcus ovis C_LI