PCR with hydrolysis probes for detection of fluoroquinolone resistance mutations in Mycobacterium tuberculosis

Abstract

Early diagnostics of resistance to fluoroquinolones facilitates early start of adequate therapy and increases the chance of a favorable outcome of the tuberculosis. Application of genetic methods permits to obtain within 1–2 days the results of Mycobacterium tuberculosis resistance detection to anti-tuberculosis drugs, unlike the classical methods requiring up to 1−2 month. The aim of the study is to develop a method for the M. tuberculosis identification and detection of point mutations in codons 90, 91, 94 of the gyrA gene associated with the resistance to fluoroquinolones. There were 88 cultures of mycobacteria studied: M. tuberculosis (n = 81), M. tuberculosis H37Rv, M. chelonae (n = 1), M. gordonae (n = 1), M. fortuitum (n = 1), and other three isolates of non-tuberculosis mycobacteria isolated from patients in the Republican Scientific and Practical Center for Pulmonology and Phthisiatry. The types of mutations in the gyrA gene were studied by the standard GenoTypeMTBDRsl method (HAIN, Germany), Sanger sequencing, and by the developed real-time PCR method. Based on the analysis of mutations in the gyrA gene in 78 isolates of M. tuberculosis, the dominant mutations were found to be mutations Asp94Gly and Ala90Val, which were identified in 21 and 27 isolates correspondingly: they accounted for 64 % of all mutations. M. tuberculosis also harbored mutations p.ASP94ALA and p.ASP94TYR/HIS in 6 (8.0 %) and 9 (12.0 %) isolates, respectively. One strain harbored a mutation at triplet 88 and one strain had a double mutation (p.ALA90VAL and p.ASP94GLY). The developed real-time PCR method demonstrated a high frequency of coincidence of results with the phenotypic determination of resistance to ofloxacin and the results testing by the standard GenoTypeMTBDRsl method and sequencing. The developed method is accomplished to identify M. tuberculosis, and discriminate mutations p.ALA90VAL, p.SER91PRO, p.ASP94ALA, p.ASP94TYR/HIS, p.ASP94GLY, p.ASP94ASN providing diagnostics of resistance to fluoroquinolones.