Abstract
BackgroundIn order to shorten the course of treatment and its effectiveness, it is essential to gain an in-depth insight into the drug resistance mechanisms of Mycobacterium tuberculosis (M. tuberculosis).MethodsIn this study, we evaluated the contribution of 26 drug efflux pumps plus target gene mutations to the drug resistance levels in multi-drug resistant (MDR)/pre-extensively drug-resistant (pre-XDR)/extensively drug-resistant (XDR) and mono-drug resistant clinical isolates of M. tuberculosis. The panels of 25 M. tuberculosis clinical strains were characterized for drug resistance-associated mutations with whole-genome sequencing and antibiotic profiles in the presence and absence of efflux inhibitor verapamil (VP).ResultsDifferent MICs were observed for the same target gene mutations. Out of the 16 MDR/pre-XDR/XDR isolates, 6 (37.5%) and 3 (18.8%) isolates demonstrated a significant decrease in rifampicin (RIF) MIC and isoniazid (INH) MIC due to the VP exposure (64 μg/mL), respectively. Susceptibility to RIF was fully restored in two isolates after VP exposure. Moreover, the efflux pump genes of Rv2938, Rv2936, Rv1145, Rv1146, Rv933, Rv1250, Rv876, Rv2333, Rv2459, Rv849, and Rv1819 were overexpressed in the presence of anti-TB drugs, showing the contribution of these efflux pumps to the overall resistance phenotype.ConclusionsOur results clearly showed that efflux systems, besides spontaneous mutations, play a role in the development of INH/RIF resistance. In addition, although VP was effective in reducing the expression of some efflux pumps, it was not very successful at the phenotypic level.
Highlights
In order to shorten the course of treatment and its effectiveness, it is essential to gain an in-depth insight into the drug resistance mechanisms of Mycobacterium tuberculosis (M. tuberculosis)
Efflux pumps are classified into six categories, including major facilitator superfamily (MFS), ATP-binding cassette (ABC), small multidrug resistance (SMR), resistance–nodulation–division (RND), multidrug and toxic compound extrusion (MATE), and proteobacterial antimicrobial compound efflux (PACE) [12, 13]
minimum inhibitory concentration (MIC) and the effect of VP Among the 16 multi-drug resistant (MDR)/pre-Extensively drug-resistant (XDR)/XDR-TB clinical isolates, PII-30 and PII-33 were resistant to all the antibiotics tested, 10 isolates were resistant to all the first-line drugs (i.e., STR, INH, RIF, and EMB), and the remaining isolates were resistant to at least two of the first-line drugs
Summary
In order to shorten the course of treatment and its effectiveness, it is essential to gain an in-depth insight into the drug resistance mechanisms of Mycobacterium tuberculosis (M. tuberculosis). Ghajavand et al Antimicrobial Resistance and Infection Control (2019) 8:70 is caused mainly by mutations in drug target genes [4], the impermeability of M. tuberculosis cell wall, and the activity of efflux pumps [5, 6]. Other mechanisms of resistance, such as efflux pumps, act synergistically with the permeability barrier to reduce the passage of antimicrobials across the bacterial outer membrane [8]. Efflux pumps are classified into six categories, including major facilitator superfamily (MFS), ATP-binding cassette (ABC), small multidrug resistance (SMR), resistance–nodulation–division (RND), multidrug and toxic compound extrusion (MATE), and proteobacterial antimicrobial compound efflux (PACE) [12, 13]. MFS, ABC, RND, and SMR efflux pumps have been found in M. tuberculosis [14]. Efflux pumps usually confer low levels of drug resistance but play a significant role in evolving to high levels of resistance in M. tuberculosis [15]
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