Abstract

Abstract. Rhodococcus equi was isolated from the lungs of six foals with bronchopneumonia. All isolates expressed 15-1 7-kd antigens by immunoblot analysis and contained a virulence-associated plasmid of 85 or 90 kb. Immunohistochemically, R. equi from all pulmonary lesions showed the expression of 15-17-kd antigens mainly in the phagocytic cells. The specific monoclonal antibody to 15-17-kd antigens of R. equi (MAb 10G5) may be an aid in the diagnosis of R. equi-induced pneumonia. Key words: Horses; immunohistochemistry; lung; Rhodococcus equi. Rhodococcus equi is an important gram-positive pathogen in foals <6 months old that causes suppurative broncho-pneumonia with abscessation, ulcerative enterocolitis, and occasionally other systemic lesions.1,2,5 This ubiquitous dis-ease has a mortality rate of 4O-8O0/o2 and reportedly accounts for more than 3 % of all foal deaths4 The pathogenesis of R. equi infection in foals remains unexplained, although there have been several reports about virulence factors associated with R. equi infection.’as Re-