Background: Streptomycin (SM) is recommended by the World Health Organization (WHO) as a part of standard regimens for retreating multidrug-resistant tuberculosis (MDR-TB) cases. The incidence of MDR-TB in retreatment cases was 19% in Thailand. To date, information on SM resistance (SMR) gene mutations correlated to the SMR of Mycobacterium tuberculosis Thai isolates is limited. In this study, the mutations in rpsL, rrs, gidB, and whiB7 were investigated and their association to SMR and the lineage of M. tuberculosis were explored.
Methods: The lineages of 287 M. tuberculosis collected from 2007 to 2011 were identified by spoligotyping. Drug susceptibility profiles were evaluated by the absolute concentration method. Mutations in SMR genes of 46 SM-resistant and 55 SM-susceptible isolates were examined by DNA sequencing.
Results: Three rpsL (Lys43Arg, Lys88Arg, and Lys88Thr) and two gidB (Trp45Ter and Gly69Asp) mutations were present exclusively in the SM resistant M. tuberculosis. Lys43Arg rpsL was the most predominant SMR mutations (69.6%) and prevailed among Beijing isolates (p<0.001). No SMR-related mutation in was found rrs. The combination of rpsL and gidB mutations provided 76.1% sensitivity for detecting SMR in M. tuberculosis Thai isolates. whiB7 was not responsible for SMR in SM resistant isolates lacking rpsL and rrs mutations. The significance of the three gidB mutations, 276A>C, 615A>G, and 330G>T, as lineage signatures for Beijing and EAI were underscored. This study identified 423G>A gidB as a novel sub-lineage marker for EAI6-BGD1.
Conclusion: Our study suggested that the majority of SMR in M. tuberculosis Thai isolates were responsible by rpsL and gidB polymorphisms constantly providing the novel lineage specific makers.
Keywords: Drug Resistance, Microbial; Mutation; Mycobacterium tuberculosis; Streptomycin; gidB; rpsL; rrs; whiB7.