121. Comparative Genomic Analysis of Escherichia coli from Liver Abscesses, Ruminal and Colonic Epithelial Tissues of Feedlot Cattle and Human Pyogenic Liver Abscesses.

Abstract Liver abscesses (LA) in feedlot cattle are polymicrobial infections, primarily caused by two subspecies of Fusobacterium necrophorum, necrophorum and funduliforme. However, a few other bacterial species, including T. pyogenes, S. enterica, E. coli and Bacteroides spp., have been reported frequently. In a recent study, E. coli was isolated from 68 of 96 (70.1%) LA samples cultured. In contrast, E. coli was isolated from 92.7% and 91.6% of corresponding ruminal and colonic epithelial tissues, respectively, indicating high colonization in gut epithelial tissues. Human cases of pyogenic LA caused by E. coli have also been reported, analogous to the gut-to-liver translocation pathogenesis associated with inflammatory colonic diseases. The contribution of E. coli to bovine LA, and the origin, whether rumen or hindgut, have not been determined. Therefore, we performed whole-genome sequencing and comparative genomic analysis of 150 E. coli strains from bovine LA (n = 65), ruminal epithelial tissues (n = 30) and colonic tissues (n = 52) to assess virulence potential and genetic relatedness between LA and gut tissue strains and to compare with human LA strains (n = 3). Virulence genes profiling of bovine strains revealed a conserved backbone of genes involved in iron acquisition, adhesion to host cells, and tissue invasion. Among the secretion systems, type VI was detected only in bovine strains and type III secretion system only in human LA strains, implying inter-bacterial competition as the dominant E. coli survival strategy in polymicrobial bovine LA compared to direct host cell interaction in human LA. Virulence genes like Tsh autotransporter (temperature sensitive hemagglutinin), enterobactin siderophore receptor genes associated with salmochelin system (iroB-N) were only detected in bovine LA strains, while hemolysin (hlyA-D) and enteroaggregative, heat stable enterotoxin (astA) gene were shared between LA and colonic strains. No virulence genes were shared between LA and ruminal tissue strains, suggesting that rumen may not be the source for E. coli LA. Colonic isolates carried the most diverse virulence gene repertoire (210 genes), which included genes detected in both LA and ruminal strains. Among colonic strains, pathotype analysis identified enteropathogenic E.coli (n = 5) and enterotoxigenic E.coli (n = 3) based on the presence of intimin (eae) and heat-stable/labile enterotoxin genes, respectively. Antimicrobial resistance genes profiling of bovine strains identified 95 resistance genes dominated by beta-lactamases (blaAmpC2, blaPBP, blaampH) and multidrug efflux determinants (acrA, acrF, mdtA, mdtP, emrA, emrY), with fluoroquinolone resistance genes (qnrB5, qnrB19) detected only in bovine LA strains. Human LA strains belonged to a sequence type 131, the globally dominant extraintestinal pathogenic E. coli (ExPEC) lineage and carried hallmark ExPEC virulence genes, including genes that encode for yersiniabactin, K1 capsule, and P fimbriae confirming that bovine and human LA E. coli are pathotypically distinct despite the shared gut-to-liver translocation pathogenesis.