Relationship between haemagglutination and HeLa-cell adherence of Rhodococcus equi

In this study, 45 Rhodococcus equi isolates from animals and humans were identified by the Api Coryne system, and serologically with monospecific antisera against capsular types 1-7, with serotypes 1 and 2 predominating. Regardless of serotype, 14 out of 31 isolates from animals and one of 14 isolates from humans expressed 15-17-kD virulence-associated proteins. In hexadecane adherence studies, serotype 2 isolates generally displayed hydrophobic surfaces. In addition, isolates of serotype 1 generally haemagglutinated erythrocytes from rabbits. Neither property appeared to be related to the occurrence of the virulence-associated proteins. By contrast, the haemagglutination reaction correlated significantly with the adherence of the bacteria to HeLa cells. This adhesion might serve as additional marker of virulence among isolates of R. equi and might be useful in epidemiological studies.