Detection and genotyping of rhodococcus equi in horses

Pneumonia caused by a soil saprophyte Rhodococcus equi is considered as one of the most important infections with high mortality rate in foals worldwide. The lack of effective treatment, control and prevention measures results in significant economical losses, and therefore urgent action is needed to overcome this infection. In this study, nasal and fecal swab samples were collected from foals reared at the state and private horse farms located in Malatya, Şanlıurfa, Bursa, Eskişehir and İzmit provinces where racehorse breeding is common. In addition, soil and water samples were taken from these enterprises. This study was carried out to investigate the presence and frequency of R. equi by bacteriological and molecular methods, and to determine genetical relationship between the field isolates by Pulsed Field Gel Electrophoresis (PFGE). Also, possible risk factors of the infection and in vitro sensitivity of the isolates to various antibiotics including ampicillin, vancomycin, erythromycin, rifampicin, clarithromycin, tetracycline, streptomycin, gentamicin were determined. Following bacteriological and molecular analyses, 10.04% (43/428) of nasal swab samples, 22.9% (98/428) of fecal swab samples, 29.4% (6/17) of soil samples and 5.8% (1/17) of water samples were confirmed as R.equi. Of the total 147 isolates confirmed R.equi, 46.2% (68/147) were identified as virulent by the PCR using vapA gene specific primers. When the antibiotic susceptibility profiles of the isolates were examined, it was found that 43.5% (64/147) of the strains were sensitive to all tested antibiotics while 2.72% (4/147) showed multiple resistance to three or more antibiotics. PFGE analyses of 65 virulent R.equi isolates produced 29 different genotype patterns within 12 clusters. In the statistical analyses of farm parametres, a positive correlation was found between the frequency of mechanical cleansing of paddocks and the absence of deaths due to R. equi infection. While virulent R. equi isolates were detected in farms with previous history of infection, the isolates obtained from farms without previous infection history were determined to be avirulent. In conclusion, the present study revealed PFGE profiles of R. equi field isolates for the first time in Turkey. As a remarkable finding, the detection of different genotypes in farms where virulent R. equi isolates were obtained necessitates comprehensive investigation of transmission sources and risk factors of the infection in addition to elucidation of genotypic features of resistant strains. It is also required to develop immunization techniques due to the fact that immune systems of foals are less improved when compared to horses. It is suggested that such data will enable the development of more effective control and prevention strategies against R. equi infections. Key words: Pneumonia, Rhodococcus equi, vapA, PFGE, PCR, antimicrobial susceptibility.