katG mutations in isoniazid-resistant strains of mycobacterium tuberculosis are not infrequent

In a recent article (7), we reported the results of mutational analysis of katG in isoniazid-resistant Mycobacterium tuberculosis strains and reached a number of conclusions, one of which was that variations in the katG gene of isoniazid-resistant isolates of M. tuberculosis are infrequent.’’ New data from our laboratory indicate that this statement is incorrect. It has been shown that deletions of the katG gene can lead to isoniazid resistance in M. tuberculosis (11), and analyses of the katG gene (1, 4, 5, 7, 9) have subsequently shown that missense mutations and small deletions in this gene are also associated with resistance to isoniazid. Similarly, it has been shown that mutations in genes such as inhA, rpoB, gyrA, gyrB, rpsL, and rrs are associated with resistance to isoniazid and other drugs (6). The single-strand conformation polymorphism (SSCP) technique was often used as an initial screen, which led to the subsequent identification of mutations by DNA sequencing