Identification and epidemiological relationship of Rhodococcus equi isolated from cases of lymphadenitis in cattle

The present study was designed to comparatively investigate 10 Rhodococcus equi isolates from cases of lymphadenitis in cattle. The isolates could be identified by cultural and biochemical properties. By serotyping the R. equi isolates 9 and 1, cultures could be classified as Nakazawa's serotypes 15 and 8, respectively. The isolates did not agglutinate rabbit erythrocytes, were uniformly susceptible to most of the antibiotics tested, did not contain plasmids nor expressed virulence-associated proteins and yielded identical patterns in protein fingerprinting. To further analyze the epidemiological relationships, the isolates were additionally subjected to DNA fingerprinting. This was performed by pulsed-field gel electrophoresis (PFGE) after digestion of the chromosomal DNA with the endonuclease AsnI. PFGE analysis of the chromosomal DNA revealed 4 DNA restriction groups with DNA pattern I with 7 isolates as predominant group and DNA pattern II to IV with one isolate, respectively. The present results indicate that a single R. equi clone belonging to Nakazawa's serotype 15 and according to PFGE to DNA restriction pattern I of the present investigation seems to be responsible for most of the cases of lymphadenitis of cattle described in this study.