Rapid Detection of Resistance Associated Mutations in Mycobacterium tuberculosis by LightCycler PCR

Rifampin (RMP) and isoniazid (INH) are important components of effective multidrug therapy and prophylaxis for M. tuberculosis infections. However, widespread use and failure of patients to complete prescribed treatment have led to the emergence of RMP- and INH-resistant strains. RMP resistance is well characterized, and 95% of all M. tuberculosis RMP-resistant clinical isolates harbor specific mutations within an 81-bp region of the rpoB gene, which is coding for the β subunit of the RNA polymerase [1]. Thus, investigation of RMP resistance is relatively straightforward. In contrast to RMP, genotype testing for INH resistance is much more complex. Several studies have reported alterations in at least four genes, one encoding for catalase-peroxidase (katG), the regulatory region of an NADH-dependent enoyl ACP reductase (inhA), and a β-Ketoacyl acyl carrier protein synthase (kasA), both involved in mycolic acid biosynthesis, and recently the involvement of an alkyl-hydroperoxidase reductase (ahpC) has been suggested [2–4]. Although the importance of the katG mutations in INH resistance has been clearly demonstrated, the involvement of the other genes is arguable. The highest proportion of mutations is in the katG gene, but only some mutations in this gene have been associated with high-level resistance (e.g., deletions or Ser315Thr), whereas others do not appear to confer any resistance to INH (e.g., Arg463Leu).