The effect of oxidative stress on the mutation rate of Mycobacterium tuberculosis with impaired catalase/peroxidase function.
OBJECTIVE
To determine the effect of oxidative stress on isoniazid-resistant Mycobacterium tuberculosis deficient in catalase/peroxidase activity to varying degrees through mutation in katG.


METHODS
The mutation rate was determined for a set of isogenic strains with different katG alleles giving different catalase and/or peroxidase activities following exposure to the oxidizing agent, hydrogen peroxide. Mutants were selected on rifampicin, and the location and nature of the mutation were identified by sequencing the rpoB gene.


RESULTS
No evidence was found to suggest that strains that had impaired catalase/peroxidase activity were hypermutable, and the presence of excess hydrogen peroxide had no effect on the mutation rate. An unusual pattern of mutations in rpoB was observed in catalase-deficient strains with only 3 of 66 having mutations within the rifampicin resistance-determining region.


CONCLUSIONS
The mutation rate of M. tuberculosis in response to oxidative stress is not increased in strains with significant deficits in catalase and peroxidase activity. Our data suggest that isoniazid-resistant strains compensate for their reduced ability to detoxify oxidative stress effectively. Interestingly, mutations were found in unusual locations at positions similar to those found in clinical isoniazid-resistant strains.
O'Sullivan
D M
DM
Centre for Medical Microbiology, Department of Infection, Hampstead Campus, University College London, Rowland Hill Street, Hampstead, London NW3 2PF, UK. denise.o'sullivan@lshtm.ac.uk
McHugh
T D
TD
Gillespie
S H
SH
D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D002374:Catalase / Q000235:genetics*; D004252:DNA Mutational Analysis; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D012321:DNA-Directed RNA Polymerases / Q000235:genetics; D024881:Drug Resistance, Bacterial; D005838:Genotype; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009154:Mutation; D009169:Mycobacterium tuberculosis / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress; D012293:Rifampin / Q000494:pharmacology; D017422:Sequence Analysis, DNA
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D016877:Oxidants; D006861:Hydrogen Peroxide; D002374:Catalase; C480353:katG protein, Mycobacterium tuberculosis; D012321:DNA-Directed RNA Polymerases; C105078:RNA polymerase beta subunit; D012293:Rifampin