Prevalence of Virulent Rhodococcus equi in Soil Environment on a Horse-Breeding Farm in Tennessee, U.S.A.

Abstract

Virulent Rhodococcus equi is an important pathogen in foals aged Key words: foal, Rhodococcus equi, soil, TennesseeRhodococcus equi is one of the most important bacterial pathogens in foals less than 3 months of age [1, 12,15,29]. Infections caused by this organism are c h a r a c t e r i z e d b y a c h r o n i c , s u p p u r a t i v e bronchopneumonia and/or enteritis [1, 12,15,29]. In horses, the disease is distributed worldwide, but little is known about the incidence of the infection in Tennessee, U. S. A.The discovery of virulence-associated antigens and virulence plasmids has permitted classification of the virulence of R. equi strains [23,30]. At least three virulence levels of R. equi have been identified: virulent, intermediate virulence, and avirulent [15]. Virulent R. equi is characterized by the presence of virulenceassociated 15-to 17-kDa antigens (VapA), and virulence plasmid DNA of 85-90 kb [23,30,33]. There are at least 11 virulence plasmid types (85-kb types I to IV, 87-kb types I and II, and 90-kb types I to V) present in VapA-positive R. equi from horses in the world by restriction fragment length polymorphism of plasmid DNAs [13,17,25,26,[31][32][33]. The virulent form has been found in pulmonary and/or intestinal lesions in foals and in the pulmonary lesions of AIDS patients (murine LD 50 =10 6 ) [28,30]. R. equi strains of intermediate virulence are identified by a virulence associated 20-kDa antigen (VapB) and virulence plasmid DNA of 79-100 kb [22]. The intermediate virulence form has been found in the submaxillary lymph nodes of pigs (murine LD 50 =10 7 ) and in the pulmonary lesions of AIDS patients [18,22]. In comparison, avirulent R. equi shows no evidence of either virulence-associated antigens or plasmid DNA (murine LD 50 >10 8 ), and is widespread in soil [15,29]. In recent studies, we have demonstrated geographic differences in the distributions of the virulenceassociated plasmids found in the Americas, Europe, Australia, Africa, Korea and Japan [2, 7-11, 13, 16, 17, 19, 25-27, 31-33, 35]. Most clinical isolates from the Americas, Australia, and Europe contain 85-kb type I or 87-kb type I plasmids [2, 7-11, 17, 19, 31]. The 85-kb type II plasmid is found only in French isolates and the 85-kb type III and type IV plasmids only in isolates from Texas [13,17,31]. These five types of virulence

Plasmid profiles of virulent Rhodococcus equiisolates from soil environment on horse-breeding farms in Hungary

“…Our recent study showed that the majority of clinical isolates from foals (123 out of 129) had an 85-kb type I plasmid and the remaining had an 87-kb type I plasmid (Makrai et al, 2002). In the present study, virulent isolates from farm 'A' were found have either an 85-kb type I or an 85-kb type III plasmid, which have been found in isolates only in Texas and Tennessee in the United States (Takai et al, 2001a(Takai et al, , 2004. Virulent isolates from farm 'B' had only an 85-kb type I plasmid.…”

Genotypic Characterization of Virulent Rhodococcus equi Isolated from the Environment of Hokkaido Native Horses in Hakodate, Hokkaido

“…Most clinical isolates from the Americas, Australia, and Europe contain 85-kb type I or 87-kb type I plasmids. The 85-kb type II, III, IV, and V plasmids are unique to France, Texas, Tennessee, and Brazil, respectively [15,20,30,33]. On the other hand, the 87-kb type II and 90-kb type I, II, III and IV plasmids have only been found in clinical or environmental isolates from Japan, and 90-kb type II and V plasmids have only been found in those from Korea [25,30,31,36].…”