Mycobacterium tuberculosis catalase and peroxidase activities and resistance to oxidative killing in human monocytes in vitro

Mycobacterium tuberculosis has a relatively high resistance to killing by h ydrogen peroxide and organic peroxides, Resistance map be mediated by mycob acterial catalase-peroxidase (KatG) and possibly by alkyl hydroperoxide red uctase (AhpC), To determine the interrelationship between sensitivity to H2 O2, catalase and peroxidase activities, and bacillary growth rates measured bath intracellularly in human monocytes and in culture medium, we examined one laboratory strain, two clinical isolates, and three recombinant strain s of M. tuberculosis with differing levels of KatG and AhpC. Five of the my cobacterial strains had intracellular doubting times of 27 to 32 h, while o ne KatG-deficient clinical isolate (ATCC 35825) doubled in similar to 76 h, Killing of mycobacteria by exogenously added H2O2 was more pronounced for intracellular bacilli than for those bacilli derived from disrupted monocyt es, Strains,vith no detectable KatG expression or catalase activity were re latively sensitive to killing (43 to 67% killing) by exogenous H2O2. Howeve r, once even minimal catalase activity was present, mycobacterial catalase activity over a 10-fold range (0.56 to 6.2 U/mg) was associated with surviv al of 85% of the bacilli. Peroxidase activity levels correlated significant ly with resistance of the mycobacterial strains to H2O2-mediated killing. A n endogenous oxidative burst induction by 4 beta-phorbol 12 beta-myristate 13 alpha-acetate treatment of infected monocytes reduced the viability of t he KatG null strain (H37Rv Inh(r)) but not the KatG-overespressing strain [ H37Rv(pMH59)]. These results suggest that mycobacterial resistance to oxida tive metabolites (including H2O2 and other peroxides) may be an important m echanism of bacillary survival within the host phagocyte.