Unraveling the microbial diversity of bovine liver abscesses: isolation, identification, and genomic characterization of the Bacteroides found in hepatic lesions.

Liver abscesses in cattle reduce animal performance, increase the environmental footprint of beef production, and cause significant economic losses. The low pH of the rumen resulting from the consumption of high grain diets damages the rumen epithelium and facilitates the translocation of opportunistic pathogens from the gastrointestinal tract into the bloodstream where they can colonize the liver, causing infection. Recently, 16s rRNA sequencing has revealed that 25%-50% of liver abscess microbiomes have prominent levels of Bacteroides. Due to the inability to reliably classify amplicon sequences beyond the genus level, the identity of these microbes remains unknown. We have employed a combination of culture-independent and culture-based methods to isolate and identify the Bacteroides associated with liver abscesses in cattle. Shotgun metagenomic sequencing and assembly of metagenome-assembled genomes generated four high-quality genomes, two of which were putatively identified as Bacteroides. These microbes were subsequently isolated from the purulent material of liver abscesses. Whole-genome sequencing conclusively identified these isolates as Bacteroides pyogenes and a previously unknown species of Bacteroides, revealing distinct differences from Bacteroides typically found in the gut. Carbohydrate utilization assays revealed that both organisms metabolize glycogen and glycosaminoglycans found in the extracellular matrix of the liver but display differences in substrate specificity. These data not only identify Bacteroides found in bovine liver abscesses but also provide new insights into the potential role that these organisms may play in this production-limiting disease. IMPORTANCE: Liver abscesses (LAs) are commonly found in cattle raised in feedlots and result from a bacterial infection of the liver. Not only are LAs a concern for animal health, but they also impact growth efficiency, animal welfare, and cost the North American beef industry upwards of $120 million per annum. Recently, it has been found that 25%-50% of liver abscess microbiomes have prominent levels of Bacteroides; however, to date, the biological relevance in LA pathogenesis and the identity of these bacteria are unknown. This research describes the isolation, identification, and genomic characterization of the Bacteroides found in bovine liver abscesses. These data provide a critical foundation for expanding our knowledge of the potential role Bacteroides play in liver abscess development and could contribute to the identification of novel targets for developing treatments to prevent this important production-limiting disease.