Identification of catalase-like activity from Mycobacterium leprae and the relationship between catalase and isonicotinic acid hydrazide (INH)

As Mycobacterium leprae proliferate inside macrophages, it has been speculated that catalase encoded by katG may protect the bacilli from deleterious effects of peroxide generated from the macrophage and may also play a crucial role in the survival of M. leprae in vivo. However, unlike that of M. tuberculosis, the katG of M. leprae has been reported to be a pseudogene, implicating that isoniazid, which is activated to a potent tuberculocidal agent by catalase, is unlikely to be of therapeutic benefit to leprosy patients. These results raise a question as to how M. leprae avoids H202-mediated killing inside macrophages. To understand the survival of M. leprae in macrophages, the present study attempted to detect catalase-like activity in M. leprae. Catalase-like activity was found in M. leprae cell lysate by the diaminobenzidine (DAB) staining method with non-denaturing polyacrylamide gel electrophoresis. An ammonium sulphate precipitation study revealed that the catalase-like activity was precipitable with 80% ammonium sulphate. The effect of isoniazid (INH) on M. leprae growth was also tested by RT-PCR and radiorespirometric assay to examine catalase-like activity in M. leprae, because INH was activated by catalase. It was found that the viability of M. leprae was decreased at a concentration of 20 microg/ml by radiorespirometric assay and it was inhibited at higher concentrations as determined by RT-PCR. These data suggest that a catalase-like activity other than that encoded by katG is present in M. leprae.