Molecular characterization of clinical isolates of Rhodococcus equi with PCR assay based on virulence plasmid marker

Abstract

Rhodococcus equi is one of the most important pathogens of foals, in which it causes a disease manifesting in pyogranulomatous bronchopneumonia, abscesses, lymphadenitis or ulcerative enterocolitis. R. equi can be pathogenic to other domestic and wild animals and humans as well. Although, R. equi is prevalent in India, the work carried out in our country has not gone much beyond isolation of organism from clinical cases of foal pneumonia. Therefore, the present study was carried out for characterization of R. equi strains isolated from clinical cases based on plasmid markers (traA, vapA and vapB genes) and antibiotic sensitivity. In the present study, 298 samples (nasal swab, 136; fecal sample, 130; soil, 28; tissue, 4) were collected and processed for isolation, identification, and characterization of R. equi via biochemical test, antimicrobial susceptibility test and PCR. A total of 28 R. equi isolates could be recovered from clinical samples. All the 28 isolates were found sensitive to chloramphenicol, erythromycin, oxytetracycline, ciprofloxacine, neomycin and rifampin while resistant to ampicillin, trimethoprim, sulphadiazine, cloxacin, amikacin, cephalexin, and kanamycin in in vitro antimicrobial assay. PCR typing based on plasmid gene markers: traA, vapA, and vapB revealed that vapA plasmid was present in 26 isolates whereas it was absent in 2 isolates. Periodic monitoring of horse farm before and after foaling season is recommended for diagnosis of R. equi and initiating requisite bio-security and therapeutic measures.