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Haemolytic and phospholipase C (PLC) activities of Rhodococcus equi
J Smola1, V Katerov, C Schalén
1Institute of Microbiology and Immunology, University of Veterinary and Pharmaceutical Sciences, Brno, Czech Republic.
Abstract:
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 to 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 from tests for trypsin, temperature and ethanol sensitivity, the haemolytic activity was primarily dependent on PI-PLC though the participation of lecithinase seemed probable. The haemolytic activity of growing strains, but not of cell-free preparations, was partially inhibited by lecithin but enhanced by cholesterol; however, cholesterol oxidase (CO) activity, known to mediate cooperative lysis of RBC sensitized with sphingomyelin-specific phospholipases C or D of some other species, did not contribute to the direct haemolysis caused by R. equi as demonstrated here.
Insights
Rhodococcus equi, a cause of foal pneumonia, exhibits hemolytic activity. This activity is mainly due to a phosphatidylinositol-specific phospholipase C (PI-PLC), challenging previous assumptions about the organism.
Area of Science:
- Veterinary Microbiology
- Equine Infectious Diseases
- Bacterial Pathogenesis
Background:
- Rhodococcus equi is an intracellular pathogen responsible for significant respiratory disease in foals.
- The organism is traditionally considered non-hemolytic, with limited understanding of its extracellular virulence factors.
- Pneumonia and lung abscesses are the primary clinical manifestations in affected foals.
Purpose of the Study:
- To investigate the hemolytic activity of Rhodococcus equi isolates.
- To identify the specific enzymes responsible for observed hemolysis.
- To characterize the biochemical properties of these hemolytic enzymes.
Main Methods:
- Testing of 14 Rhodococcus equi isolates for hemolytic activity on agar plates with washed red blood cells from various species.
- Biochemical characterization of hemolytic activity, including sensitivity to trypsin, temperature, and ethanol.
- Enzymatic assays to identify lecithinase and phospholipase C (PI-PLC) activities.
- Investigation of the role of cholesterol and cholesterol oxidase (CO) in hemolysis.
Main Results:
- 13 out of 14 Rhodococcus equi isolates demonstrated hemolytic activity against red blood cells from rabbits, dogs, horses, and humans.
- Two novel enzymatic activities were identified: lecithinase and phosphatidylinositol-specific phospholipase C (PI-PLC).
- Hemolytic activity was primarily attributed to PI-PLC, with a probable contribution from lecithinase.
- Cholesterol enhanced hemolysis, while cholesterol oxidase activity did not directly contribute.
Conclusions:
- Rhodococcus equi possesses significant hemolytic activity, contrary to previous beliefs.
- Phosphatidylinositol-specific phospholipase C (PI-PLC) is the key enzyme mediating this hemolysis.
- These findings provide new insights into the pathogenesis of Rhodococcus equi infections in foals.