Genotypic differences between strains of the opportunistic pathogen Corynebacterium bovis isolated from humans, cows, and rodents

Abstract

Corynebacterium bovis is an opportunistic bacterial pathogen shown to cause eye and prosthetic joint infections as well as abscesses in humans, mastitis in dairy cattle, and skin disease in laboratory mice and rats. Little is known about the genetic characteristics and genomic diversity of C. bovis because only a single draft genome is available for the species. The overall aim of this study was to sequence and compare the genome of C. bovis isolates obtained from different species, locations, and time points. Whole-genome sequencing was conducted on 20 C. bovis isolates (six human, four bovine, nine mouse and one rat) using the Illumina MiSeq platform and submitted to various comparative analysis tools. Sequencing generated high-quality contigs (over 2.53 Mbp) that were comparable to the only reported assembly using C. bovis DSM 20582T (97.8 ± 0.36% completeness). The number of protein-coding DNA sequences (2,174 ± 12.4) was similar among all isolates. A Corynebacterium genus neighbor-joining tree was created, which revealed Corynebacterium falsenii as the nearest neighbor to C. bovis (95.87% similarity), although the reciprocal comparison shows Corynebacterium jeikeium as closest neighbor to C. falsenii. Interestingly, the average nucleotide identity demonstrated that the C. bovis isolates clustered by host, with human and bovine isolates clustering together, and the mouse and rat isolates forming a separate group. The average number of genomic islands and putative virulence factors were significantly higher (p<0.001) in the mouse and rat isolates as compared to human/bovine isolates. Corynebacterium bovis’ pan-genome contained a total of 3,067 genes of which 1,354 represented core genes. The known core genes of all isolates were primarily related to ‘‘metabolism” and ‘‘information storage/processing.” However, most genes were classified as ‘‘function unknown” or “unclassified”. Surprisingly, no intact prophages were found in any isolate; however, almost all isolates had at least one complete CRISPR-Cas system.