[Characterization of the katG, inhA, ahpC, kasA, and oxyR gene mutations in isoniazid-resistant and susceptible strain of Mycobacterium tuberculosis by automated DNA sequencing].

OBJECTIVE

To study the characteristics of katG, inhA, ahpC, kasA, and oxyR gene mutations in isoniazid-resistant clinical isolates of Mycobacterium tuberculosis.

METHODS

A total of 101 isoniazid-resistant and 43 susceptible strains of Mycobacterium tuberculosis were analyzed by PCR and sequence analysis of their katG, inhA, ahpC, kasA, and oxyR genes.

RESULTS

(1) Sequencing of katG from 101 INH-resistant strains showed point mutations, small deletions or insertions in 81 isolates (80.2%), but no complete deletions were identified. The mutations at 16 position were found for the first time. Point mutations at position 315 were found in the genomes of 38.6% (39/101) of isoniazid-resistant strains. Low level isoniazid resistant strains (1 microg/ml) had higher mutation frequency at 315-Ser than high level isoniazid resistant strains (10 microg/ml; chi(2) = 9.31, P < 0.05). Mutations at position 463 were detected in 58 (57.4%) isoniazid-resistant strains. Arg463leu was also present in 23 of 43 susceptible strains. (2) Mutations in inhA genes were identified in 5 isoniazid-resistant isolates (4.9%). None of the susceptible strains contained any mutation in inhA genes. (3) Only 3 isolates in the 101 (2.97%) isoniazid-resistant clinical isolates had mutations in ahpC genes. No mutations were identified in the ahpC genes in 43 isoniazid-susceptible isolates. (4) Mutations in kasA genes were present in 17 of 101 (16.8%) isoniazid-resistant isolates. However, G312S was also present in 3 of 43 susceptible strains. (5) None of the isoniazid-resistant strains and susceptible isolates contained oxyR gene mutation. (6) Taken together, 91 of 101 (90%) isoniazid-resistant strains had mutations in katG, inhA, ahpC, and kasA genes which were associated with drug resistance.

CONCLUSION

These studies provide further evidence supporting the association between katG, inhA, ahpC, and kasA gene mutations and INH resistance in Mycobacterium tuberculosis, while other mechanisms of INH resistant may exist.