Rapid Detection of Mycobacterium tuberculosis Strains Resistant to Isoniazid and/or Rifampicin: Standardization of Multiplex Polymerase Chain Reaction Analysis.

Drug susceptibility testing using molecular techniques can enhance the identification of drug-resistant Mycobacterium tuberculosis Two multiplex real-time polymerase chain reaction (qPCR) assays were developed to detect the most common resistance-associated mutations to isoniazid (katGS315T, inhA-15C → T), and rifampicin (rpoBH526Y and rpoBS531L). To assess the species specificity of the qPCR, we selected 31 nontuberculous mycobacteria (NTM) reference strains belonging to 17 species from the public collection of mycobacterial cultures (BCCM/ITM). Additionally, we tested 17 isoniazid and/or rifampicin-resistant strains with other mutations in the target genes to assess mutation specificity. The limit of detection for all the targeted mutations was 20 bacilli/reaction. Multiplex 1 showed 90%, 95%, and 100% efficiency for wild type (WT), Mut katGS315T, and Mut rpoBS531L, respectively; whereas Multiplex 2 showed 97%, 94%, and 90% efficiency for WT, Mut inhA-15, and Mut rpoBH526Y, respectively. Three of 17 strains that presented other mutations in the target genes were identified as rifampicin resistant and only 3/31 NTM showed a similar melting temperature to rpoBL531 and/or katGT315 mutants. Thus, our proposed cascade of specific tuberculosis detection followed by drug resistance testing showed sensitivities for katGS315T, rpoBS531L, rpoBH526Y, and inhA-15 detection of 100%, 100%, 100%, and 96%, respectively; and specificities of 98%, 95%, 100%, and 100, respectively.