Interaction between <em>rpsL</em> and <em>gyrA </em>mutations affects the fitness and dual resistance of <em>Mycobacterium tuberculosis</em> clinical isolates against streptomycin and fluoroquinolones

Abstract

BackgroundThe interaction between different drug-resistant mutations is important to the development of drug resistance and its evolution. In this study, we aimed to reveal the potential relationships between mutations conferring resistance to two important antituberculosis drugs streptomycin (STR) and fluoroquinolones (FLQ).Materials and methodsWe used an in vitro competitive fitness assay to reveal the interactions between different mutations of rpsL and gyrA in drug-resistant Mycobacterium smegmatis, followed by the analysis of the frequency of rpsL and gyrA mutation combinations in 213 STR–FLQ dual-resistant clinical Mycobacterium tuberculosis isolates from Sichuan region, which was also investigated by the whole genome data from 3,056 global clinical M. tuberculosis isolates.ResultsThe strains with K43R and K88R mutation in rpsL showed no difference in relative fitness compared with their susceptible ancestor, while K43N, K43M, K43T, and K88E exhibited a significantly lower relative fitness (P<0.05). For the FLQ-resistant mutants, all mutation types showed no difference in their relative fitness. Among STR–FLQ dual-resistant M. smegmatis strains, a lower fitness was detected in those with K43N/M/T and K88E instead of K43R and K88R mutations in rpsL. Among M. tuberculosis isolates harboring rpsL and gyrA dual mutations, the most two frequent combinatorial mutation types were K43R/D94G (n=37) and K43R/A90V (n=24), with the former being the most frequent one by both in vitro tests and clinical survey.ConclusionOur results suggest that the interaction between rpsL and gyrA mutations affects the fitness cost in STR–FLQ dual-resistant M. smegmatis and also the predilection of mutation combinations in clinical M. tuberculosis isolates.

Heterogeneous Streptomycin Resistance Level Among Mycobacterium tuberculosis Strains From the Same Transmission Cluster

“…(Okamoto et al, 2007;Jagielski et al, 2014;Khosravi et al, 2017;Islam et al, 2020;Shrestha et al, 2020). The type of DR mutation might associate with the M. tuberculosis lineage and influence the resistance level and fitness (Spies et al, 2011;Ballif et al, 2012;Miotto et al, 2017;Macedo et al, 2018;Sun et al, 2018). The relative fitness of drug resistant vs. susceptible strains has been highlighted as a key factor driving the transmission of DR M. tuberculosis (Ballif et al, 2012;Morcillo et al, 2014;Knight et al, 2015).…”

Phenotypic and genotypic characterization of levofloxacin- and moxifloxacin-resistant Mycobacterium tuberculosis clinical isolates in southern China

“…In line with older FQ agents, the two new agents (LVX and MXF) inhibit DNA gyrase (a type II topoisomerase composed of α and β subunits), restricting the cell's capacity for DNA replication and transcription (12,13). Mutations in gyrA and gyrB genes, particularly in the quinolone resistance-determining region (QRDR) of gyrA (codons 74 to 113) and gyrB (codons 500 to 540), are the main reason of FQ resistance in MTB (14).…”

The Neglected Contribution of Streptomycin to the Tuberculosis Drug Resistance Problem

“…The fact that several studies show that, in TB, cross-resistance combining STR with other first and second-line antibiotics is common [ 11 , 34 , 67 , 95 , 96 , 97 , 98 , 99 ] could be due to the early introduction of STR in the history of antibiotic use and the current prevalence of specific STR mutations with low fitness costs. However, considering the reported studies gives strength to the hypothesis that isolates that become STR resistant could better compensate the cost of mutations conferring resistance to other antibiotics, eventually becoming more predisposed to polyresistance.…”