EXPRESSION OF VIRULENCE-ASSOCIATED ANTIGENS OF RHODOCOCCUS-EQUI IS REGULATED BY TEMPERATURE AND PH

We recently reported that there are two different virulence-associated antigens correlated with virulence levels in Rhodococcus equi isolate s from AIDS patients: virulent R. equi that kills mice with 10(6) cell s expresses 15- to 17-kDa antigens and intermediately virulent R. equi that kills mice with 10(7) cells expresses a 20-kDa antigen. Environm ental parameters were evaluated for their effects on the expression of these virulence-associated antigens in virulent R. equi strains by im munoblotting using monoclonal antibodies in this study. Expression of these two virulence-associated antigens of R. equi was regulated by pH and temperature; the antigens were produced maximally when the isolat es were grown at 38 C and pH 6.5, but were not produced when grown at 38 C and pH 8, nor at temperatures below 30 C. The 20-kDa antigen was found to be located on the cell surface, as were the 15- to 17-kDa ant igens, and showed susceptibility to proteolysis by trypsin. These resu lts indicate that expression of the virulence-associated antigens of R . equi is dependent on the environmental conditions.