Pathogenicity and genomic features of vapN-harboring Rhodococcus equi isolated from human patients

Elsevier

Available online 2 July 2021, 151519

International Journal of Medical MicrobiologyHighlights•

This study showed the pathogenicity and genomic features of vapN-harboring R. equi.

VapN-producing strains showed the proliferation in cultured macrophages.

VapN-producing strains reproduced fatal necrotizing granulomatous inflammation.

Both VapN-producing and non-producing strains have nearly identical pVAPNs.

More genomic analyses are needed to explain the mechanism of VapN expression.

Abstract

Rhodococcus equi is a saprophytic soil bacterium and intracellular pathogen that causes refractory suppurative pneumonia in foals and has emerged as a pathogenic cause of zoonotic disease. Several studies have reported human infections caused by R. equi harboring a recently described third type of virulence plasmid, the ruminant-associated pVAPN, which carries the vapN virulence determinant. Herein, we analyzed pathogenicity and genomic features of nine vapN-harboring R. equi isolated from human patients with and without HIV/AIDS. Four of these strains showed significant VapN production and proliferation in cultured macrophages. These strains were lethally pathogenic after inoculation with 1.0 × 108 CFU in mice and reproduced a necrotizing granulomatous inflammation in the liver and spleen similar to that observed in humans. Additionally, we determined entire genome sequences of all nine strains. Lengths of sequences were 5.0–5.3 Mbp, and GC contents were 68.7%–68.8%. All strains harbored a 120- or 125-kbp linear plasmid carrying vapN (Type I or Type II pVAPN) classified on the basis of differences in the distal sequences on the 3' side. Interestingly, VapN production differed significantly among strains harboring nearly identical types of pVAPN with variation limited to several SNPs and short base pair indels. The pVAPN sequences possessed by the VapN-producing strains did not retain any common genetic characteristics, and more detailed analyses, including chromosomal genes, are needed to further elucidate the VapN expression mechanism.

Keywords

Plasmid

Rhodococcus equi

virulence-associated protein N

whole-genome sequencing

© 2021 Published by Elsevier GmbH.

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