Effect of inhA and katG on isoniazid resistance and virulence of Mycobacterium bovis

Abstract

Isoniazid (INH) resistance of the Mycobacterium tuberculosis Complex (MtbC) is associated with both loss of catalase activity and mutation of the inhA gene. However, the relative contributions of these changes to resistance and to the loss of virulence for guinea-pigs is unknown. In this study, a virulent strain of Mycobacterium bovis, a member of the MtbC, was exposed to increasing concentrations of INH. Two INH-resistant strains were produced which had lost catalase activity. Strain WAg405, which had a higher resistance to INH, also had a mutation in the inhA gene. This demonstrated that loss of catalase activity and mutation of inhA had a cumulative effect on INH resistance. When a functional katG gene was integrated into the genome of WAg405 the INH resistance was greatly reduced. This indicated that most of the resistance had been caused by loss of catalase activity. While the parent INH-sensitive strain was virulent for guinea-pigs, the INH-resistant strains were significantly less virulent. Integration of a functional katG gene into the most resistant strain restored full virulence. This clearly established that katG is a virulence factor for M. bovis and that mutation of the inhA gene has no effect on virulence.

Extracellular enzyme activities potentially involved in the pathogenicity of Mycobacterium tuberculosis

“…Furthermore, integration of a functional katG, a gene that encodes catalaseperoxidase, into an attenuated catalase-negative strain of M. bovis restored full virulence for guinea pigs (Wilson et al, 1995), thereby establishing that catalase and/or peroxidase are virulence factors at least in this host. These enzymes, as well as superoxide dismutase, have been regarded for a long time as putative candidates to resist the toxic oxygen intermediates produced by host phagocytes.…”

The rapid diagnosis of isoniazid and rifampicin resistance in Mycobacterium tuberculosis -- a molecular story

“…However, the situation is much more complex if isoniazid resistance is considered. Mutations in at least four genes or gene complexes are known to be involved in resistance, including katG which encodes the catalase-peroxidase enzyme, inhA/ mabA which is involved in fatty acid biosynthesis, ahpC which encodes the alkyl hydroperoxide reductase C, and oxyR which is the oxidative stress regulator [16][17][18][19][20][21][22][23][24]. To detect isoniazid resistance would require systems that were capable of detecting mutations at multiple sites simultaneously, and such systems are able currently to predict isoniazid resistance only in c. 85% of cultures [24].…”

The multifunctional histone-like protein Lsr2 protects mycobacteria against reactive oxygen intermediates

“…Nitric oxide synthase-2 (NOS2) knockout mice, which cannot generate RNI, and phagocyte oxidase (PHOX) knockout mice, which cannot generate ROI, exhibit increased sensitivity to M. tuberculosis infection (2,3,4). Conversely, M. tuberculosis strains deficient in catalaseperoxidase (KatG), or other antioxidative mechanisms, are less virulent in mouse models (5,6). Moreover, the observation that children with defective oxidative burst mechanisms because of chronic granulomatous disease develop numerous complications from bacillus Calmette-Guérin vaccination and have a high incidence of tuberculosis, highlights the importance of ROI in protection against M. tuberculosis in humans (7).…”