Rhodococcus equiU19 strain harbors a nonmobilizable virulence plasmid

Area of Science:

• Microbiology
• Veterinary Science
• Molecular Biology

Background:

• Rhodococcus equi is a significant pathogen causing pyogenic pneumonia in foals.
• The virulence-associated protein A (VapA), encoded by the pVAPA plasmid, is crucial for R. equi pathogenicity.
• Understanding plasmid genetics is key to controlling R. equi infections.

Purpose of the Study:

• To analyze the virulence of R. equi strain U19 and the genetic characteristics of its pVAPA_U19 plasmid.
• To compare pVAPA_U19 with other known pVAPA plasmids, particularly regarding virulence and mobility.
• To investigate the factors contributing to R. equi pathogenicity and potential transmission mechanisms.

Main Methods:

• Analysis of VapA expression under varying temperature and pH conditions.
• Restriction fragment length polymorphism (RFLP) analysis of pVAPA_U19.
• Whole-genome sequencing of the pVAPA_U19 plasmid.
• Coculture experiments to assess plasmid conjugation capability.

Main Results:

• R. equi U19 expressed VapA, showing temperature and pH regulation, and proliferated within macrophages.
• pVAPA_U19 shares significant genetic similarity with pREAT701, including the vapA pathogenicity island and replication genes.
• pVAPA_U19 lacks specific open reading frames (ORF26-ORF45) found in pREAT701, which include mobility (MOB) and mating pair formation (MPF) genes.
• Conjugation experiments confirmed that pVAPA_U19 is nonmobilizable and cannot transfer itself between bacterial strains.

Conclusions:

• The pVAPA_U19 plasmid contributes to R. equi virulence and is maintained similarly to other pVAPA plasmids.
• The absence of MOB and MPF genes renders pVAPA_U19 nonconjugatable, suggesting limited horizontal transfer potential.
• These findings enhance our understanding of R. equi pathogenesis and plasmid biology.