Genotypic detection of multidrug resistant Mycobacterium tuberculosis strains

Multidrug-resistant Mycobacterium tuberculosis strains can now be rapidly detected using genetic methods. Most mutations that induce resistance to rifampicin and isoniazid appear in the core region of rpoB gene and, respectively, in codon 315 of katG gene and in the promoter region mabA-inhA:-15. Our objective was the assessment of cost and test performance of multiplex allele-specific polymerase chain reaction (MAS-PCR) for the detection of mutations that induce rifampicin and isoniazid resistance in M. tuberculosis. We have analyzed 83 non-duplicate M. tuberculosis isolates using conventional phenotypic drug susceptibility testing and a single-step MAS-PCR assay for simultaneous detection of mutations in codons 531, 526 and 516 of rpoB gene, as well as in codon 315 of katG and in the promoter region mabA-inhA:-15. We have calculated the cost of genotypic testing/strain. MAS-PCR technique detected rifampicin resistance with 88.88% sensitivity and 100% specificity in comparison to phenotypic testing, while isoniazid resistance was detected with 95.06% sensitivity and 100% specificity. The cost of genotypic testing/strain was approximately US$ 1.62. MAS-PCR technique demonstrated good sensitivity and specificity for detection of mutations that induce rifampicin and isoniazid resistance, and therefore can be used as a rapid and inexpensive method for diagnosis of multidrug resistant tuberculosis.