PS11-4. Phenotypic and Genomic Characterization of the Bacteroides purulensis sp. nov. Type Strain, Isolated from Purulent Material of A Bovine Liver Abscess.

Abstract Liver abscesses (LA) are a common and economically important disease in cattle and is historically attributed to Fusobacterium necrophorum. Recent work has found that LA are polymicrobial, with members of the genus Bacteroides also frequently identified in abscess microbiomes. We have conducted phenotypic and genomic characterization of the type strain of a novel species of bacteria, Bacteroides purulensis sp. nov., isolated from a liver abscess. Herein we describe the results of this work for six bacterial strains (LA260, LA263, LA265T, LA268, LA270, and LA272) isolated from the purulent material of a liver abscess that was collected from a beef cow in Canada.B. purulensis is a Gram-negative, rod-shaped, obligately anaerobic, non-motile bacteria. Comparative analysis of full-length 16S rRNA gene sequences (1,526 bp) within the genus Bacteroides showed 100% similarity among the six strains, and that they formed a distinct lineage that was most closely related to Bacteroides heparinolyticus (93.6%) and Bacteroides zoogleoformans (91.3%). Phylogenetic trees constructed using neighbor-joining, maximum-likelihood, and maximum-parsimony methods consistently supported this placement within the Bacteroides phylogenetic tree. Whole genome analysis of strain LA265T revealed a genome size of 3.03 Mb with a G+C content of 47.4 mol%. Values for Average nucleotide identity (ANI < 91%) and digital DNA–DNA hybridization (dDDH < 42.5%), relative to the closest type strains, were below accepted species delineation thresholds. These results confirmed that B. purulensis represents a novel species.Phenotypically, the strains exhibited growth at 30–42 °C with an optimum at 37 °C over a pH range of 6.5–8.0, and at ionic strength of ≤ 1.0% NaCl. The isolates were negative for catalase, oxidase, indole production, and esculin hydrolysis. Distinct biochemical characteristics, including carbohydrate utilization patterns and enzyme activities, differentiate the isolates from closely related species. The predominant cellular fatty acids were saturated fatty acids, and included C16:0, C18:0, and branched C15:0. MALDI-TOF MS analysis further supported their distinction from existing reference taxa.Based on combined phylogenetic, genomic, phenotypic, and metabolic evidence, a novel species within the genus Bacteroides, the name Bacteroides purulensis sp. nov. is proposed, and strain LA265T is designated as the type strain. It is currently unclear what role this organism may play in LA formation and further research is needed. Nonetheless, these findings expand our current understanding of liver abscess microbiology, and provide foundational knowledge for future studies investigating if Bacteroides has an active role in this disease.