Abstract
Rhodococcus equi can cause severe infections in people, particularly in immunocompromised individuals. The R. equi virulence plasmids (vap) encoding vapA and vapB are linked to development of infections in domestic animals. Recently, a novel virulence plasmid, vapN, was identified in isolates cultured from cattle, but its prevalence or significance in human R. equi infections has not been extensively studied. To determine the prevalence of vapN in a diverse collection of human-derived isolates from different countries, 65 R. equi isolates collected by various institutions from 1984 to 2002 were screened for the presence of vapN and other virulence plasmids through polymerase chain reaction (PCR) using redesigned primer sets. Of the isolates that carried plasmids, 43% (16/37) were vapN-positive and fewer were vapB or vapA-positive (30 and 16%, respectively). This is the first report of vapN carriage in R. equi isolated from human infections. One isolate (H-30) carried vapN but did not amplify the conjugal plasmid transfer gene traA associated with carriage of vap, which could be explained by sequence variation within the traA gene. Another isolate (H-55) amplified traA, but did not amplify vapA, B, or N (traA+ vapABN-) with previously described primer sets or those developed for this study. The H-55 traA sequence had 98% identity to traA sequences in vapA plasmids, which suggests that it may carry a variant of previously characterized virulence plasmids or a novel virulence plasmid. Carriage of vapN in R. equi isolates derived from people is not uncommon and more research is needed to determine its significance in the epidemiology and pathogenesis of human R. equi infections.
Highlights
Rhodococcus equi is a Gram-positive, facultative intracellular coccobacillus that causes infection in humans and a wide variety of animals [1]
R. equi infections are often opportunistic and commonly occur in immunocompromised individuals, with most reports in organ transplant recipients, hematopoietic cancer patients, or in people infected with human immunodeficiency virus (HIV) that progressed to acquired immunodeficiency syndrome (AIDS) [2, 3]
The goals of this study were to develop specific polymerase chain reaction (PCR) primers for detection of vap plasmids that could be used with genomic DNA (gDNA) and to screen a historic database of human-derived R. equi isolates for vap plasmids to determine prevalence of vapN carriage
Summary
Rhodococcus equi is a Gram-positive, facultative intracellular coccobacillus that causes infection in humans and a wide variety of animals [1]. R. equi infections are often opportunistic and commonly occur in immunocompromised individuals, with most reports in organ transplant recipients, hematopoietic cancer patients, or in people infected with human immunodeficiency virus (HIV) that progressed to acquired immunodeficiency syndrome (AIDS) [2, 3]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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