Genomic analysis of a novel Rhodococcus (Prescottella) equi isolate from a bovine host

Abstract

Rhodococcus (Prescottella) equi causes pneumonia-like infections in foals with high mortality rates and can also infect a number of other animals. R. equi is also emerging as an opportunistic human pathogen. In this study, we have sequenced the genome of a novel R. equi isolate, B0269, isolated from the faeces of a bovine host. Comparative genomic analyses with seven other published R. equi genomes, including those from equine or human sources, revealed a pangenome comprising of 6876 genes with 4141 genes in the core genome. Two hundred and 75 genes were specific to the bovine isolate, mostly encoding hypothetical proteins of unknown function. However, these genes include four copies of terA and five copies of terD genes that may be involved in responding to chemical stress. Virulence characteristics in R. equi are associated with the presence of large plasmids carrying a pathogenicity island, including genes from the vap multigene family. A BLAST search of the protein sequences from known virulence-associated plasmids (pVAPA, pVAPB and pVAPN) revealed a similar plasmid backbone on two contigs in bovine isolate B0269; however, no homologues of the main virulence-associated genes, vapA, vapB or vapN, were identified. In summary, this study confirms that R. equi genomes are highly conserved and reports the presence of an apparently novel plasmid in the bovine isolate B0269 that needs further characterisation to understand its potential involvement in virulence properties.

Keywords: Bovine; Pathogenicity island; Plasmid; Pneumonia; Rhodococcus equi; Virulence.

Fig. 1

1. Heat maps showing a pairwise average amino-acid identities (AAI) and b pairwise average nucleotide identities (ANI) among R. equi genomes. The source of isolation where known, are mentioned in parentheses next to the strain designations: [B] bovine, [E] equine, [En] environment, [H] human and [S] swine hosts