Rhodococcus equiU19 strain harbors a nonmobilizable virulence plasmid

Abstract

Rhodococcus equiis the causative agent of pyogenic pneumonia in foals, and a virulence‐associated protein A (VapA) encoded on the pVAPA virulence plasmid is important for its pathogenicity. In this study, we analyzed the virulence of R. equi strain U19, originally isolated in the Netherlands in 1997 and the genetic characteristics of the pVAPA_U19 plasmid. U19 expressed VapA that was regulated by temperature and pH and underwent significant intracellular proliferation in macrophages. The restriction fragment length polymorphism of pVAPA_U19 digested with EcoRI was similar to that of pREAT701 (85 kb Type I) harbored by R. equi ATCC33701, although the band pattern at 10–20 kb differed. Whole‐genome sequencing showed that pVAPA_U19 was 51,684 bp in length and that the vapA pathogenicity island region and the replication/participation were almost identical to those in pREAT701. By contrast, the open reading frames (ORF26–ORF45) genes of pREAT701 (approximately 29,000 bp) were absent from pVAPA_U19. In this lacking region, mobility (MOB) genes, such as relaxase, which allow conjugative DNA processing, and the mating pair formation (MPF) genes, which are a form of the Type IV secretion system and provide the mating channel, were present. Coculture between U19 and five different recipient strains (two plasmid‐cured strains and three cryptic plasmid‐harboring strains) demonstrated that pVAPA_U19 could not support conjugation. Therefore, pVAPA_U19 does not differ significantly from the previously reported pVAPA in terms of virulence and plasmid replication and maintenance but is a nonmobilizable plasmid unable to cause conjugation because of the absence of genes related to MOB and MPF.

Virulence plasmids in clinical isolates of Rhodococcus equi from sick foals in the Netherlands

“…This plasmid is similar to the 85‐kb type I plasmid in terms of pathogenicity and plasmid maintenance, but it lacks almost all genes related to mobility (MOB) genes, which allow conjugative DNA processing, and mating pair formation (MPF) genes, which are a form of the type IV secretion system and provide the mating channel (Suzuki et al . 2022).…”

“…Still, it is a non‐mobilizable plasmid unable to induce conjugation due to the absence of genes related to MOB and MPF (Suzuki et al . 2022). This new variant was tentatively designated as the 52‐kb plasmid.…”

“…Of the 120 isolates, 117 (97Á5%) contained the 85-kb type I plasmid, 2 (1Á7%) contained the 87-type I plasmid and 1 (0Á8%) contained a new variant, a 52-kb virulence plasmid, which was recently reported as the smallest non-selftransmissible virulence plasmid in R. equi. This plasmid is similar to the 85-kb type I plasmid in terms of pathogenicity and plasmid maintenance, but it lacks almost all genes related to mobility (MOB) genes, which allow conjugative DNA processing, and mating pair formation (MPF) genes, which are a form of the type IV secretion system and provide the mating channel (Suzuki et al 2022).…”

“…More recently, Suzuki et al . (2022) have reported the 14th new variant of pVAPA_U19, 52‐kb in an isolate from the tracheal wash of a foal in the Netherlands.…”

“…To date, 13 closely related plasmid types (85-kb types I, II, III, IV and V, 87-kb types I, II and III and 90-kb types I, II, III, IV and V) have been found in virulent R. equi. More recently, Suzuki et al (2022) have reported the 14th new variant of pVAPA_U19, 52-kb in an isolate from the tracheal wash of a foal in the Netherlands.…”