Virulence-associated protein characterisation of Rhodococcus equi isolatedfrom bovine lymph nodes

Rhodococcus equi has a low pathogenicity in cattle, but it occasionally cau ses lymph node granulomas, which are detected at abattoir post mortem inspe ction, and must be distinguished from tuberculous granulomas. Lymph node le sions were detected in 6719 cattle, from a total of 3,263.622 cattle examin ed post mortem in abattoirs, in the Republic of Ireland, during 1997 and 19 98. Histological examination was performed on all lesions, principally for the purpose of identifying animals with tuberculosis. A total of 1122 of th e lesions were cultured on blood agar and on Stonebrinks and Lowenstein-Jen sen medium containing pyruvate, because the histological findings were diff icult to interpret or were suggestive of R. equi infection. R. equi was iso lated from 264 lesions. Almost all of the R. equi granulomas were confined to a single lymph node, and were present predominantly in the retropharynge al, bronchial and mediastinal lymph nodes. R. equi granulomas were present in a significantly higher proportion of the lesions detected in steers and heifers compared to cows. The prevalence in the total population of 3.3 mil lion cattle examined post mortem was 0.008%. The 15-17 kDa antigens, associ ated with virulence in this organism, and the 20 kDa antigen, associated wi th intermediate virulence, were not detected in isolates from 146 cattle, a nalysed by immunoblot assays. A PCR assay to detect the plasmid gene encodi ng the 15-17 kDa antigens was also negative for isolates from these 146 ani mals. Plasmids were not detected in 30 isolates which were examined. (C) 20 01 Elsevier Science B.V. All rights reserved.