HEMOLYTIC AND PHOSPHOLIPASE-C (PLC) ACTIVITIES OF RHODOCOCCUS-EQUI

Rhodococcus equi, an intracellular organism causing pneumonia and lung abscesses in foals, is generally thought to be non-haemolytic. In the present study, however, 13 of 14 representative isolates were found t o be haemolytic when tested on agar media containing washed red blood cells rather than whole blood. Red cells of rabbits, dogs, horses and man were more sensitive to lysis than were those of ruminants. Two new enzymatic activities of the species were defined: a lecithinase and a phosphatidylinositol-specific phospholipase C (PI-PLC). As judged fro m tests for trypsin, temperature and ethanol sensitivity, the haemolyt ic activity was primarily dependent on PI-PLC though the participation of lecithinase seemed probable. The haemolytic activity of growing st rains, but not of cell-free preparations, was partially inhibited by l ecithin but enhanced by cholesterol; however, cholesterol oxidase (CO) activity, known to mediate cooperative lysis of RBC sensitized with s phingomyelin-specific phospholipases C or D of some other species, did not contribute to the direct haemolysis caused by R. equi as demonstr ated here.