Short CommunicationCharacterization of gyrA and gyrB mutations associated with fluoroquinolone resistance in Mycobacterium tuberculosis isolates from Morocco
Introduction
During the last decades, the emergence of drug resistance in Mycobacterium tuberculosis has made an effective control strategy for tuberculosis (TB) indispensable. TB control is hampered by the rapid spread of multidrug-resistant (MDR) and extensively drug-resistant (XDR) TB, both in new and previously treated cases, which warrants the need for decisive action to adjust therapies and to prevent further resistance [1].
Fluoroquinolones (FQs) are the most effective antimicrobial agents used to treat MDR-TB. Unfortunately, FQs have been widely prescribed in the treatment of undiagnosed respiratory bacterial infections [2], hence their uncontrolled and inappropriate use may contribute to FQ resistance in M. tuberculosis, which may influence the clinical outcome for MDR-TB patients. Thus, recognising the sensitive/resistant FQ status will provide new insights to develop appropriate regimens for MDR-TB patients.
Resistance to FQs such as ofloxacin, commonly used to treat MDR-TB, is thought to be mediated by mutations in the target genes gyrA and, less frequently, gyrB, which encode the respective subunits of DNA topoisomerase gyrase [3]. Most mutations conferring resistance to FQs are known to be accumulated in two short discrete regions of gyrA and gyrB termed the quinolone resistance-determining regions (QRDRs) [4], [5].
FQ resistance is increasingly reported worldwide. Hence, the present preliminary study was planned to assess the mutational status of gyrA and gyrB genes both in pan-susceptible and MDR-TB isolates from Morocco and to analyse the relationship between genotypes and FQ drug resistance patterns.
Section snippets
Sample collection
A collection of 30 MDR-TB and 20 pan-susceptible M. tuberculosis strains selected from our laboratory collection was included in this work [6], [7]. These strains were isolated from patients with pulmonary TB. The clinical status of patients revealed that 18 (36%) were new cases, 15 (30%) were relapses, 10 (20%) had failed treatment and 7 (14%) had defaulted.
It should be underlined that: (i) only good quality bacterial lysis was subject to the present study: in fact, many samples were damaged
Results
Both susceptible (n = 20) and MDR-TB (n = 30) isolates were subject to DNA sequencing of the gyrA and gyrB genes. None of susceptible isolates harboured any single nucleotide polymorphisms (SNPs) in the respective genes. Among the 30 genotypically MDR-TB strains, 9 (30%) had FQ resistance mutations in the gyrA gene but none harboured any SNPs in the gyrB gene. Genotyping results regarding resistance to FQs are reported in Table 1. The results showed that the most prevalent resistance mutation in
Discussion
Early diagnosis of MDR/XDR-TB is crucially important for a rational treatment regimen to prevent further transmission of drug-resistant TB. The present study focused on FQ resistance. The results showed that 30% (9/30) of MDR-TB isolates carried resistance mutations in gyrA at codons 90 (56%; 5/9) and 94 (44%; 4/9), with Ala90Thr being the most common (n = 5). These findings are in agreement with previously reported data, although it is suggested that mutations at codon 94, rather than codon 90,
Conclusion
The results of this study demonstrate the utility of detection of mutations associated with resistance to FQs, which is crucial for predicting phenotypic resistance to FQs, for optimising TB treatment and for preventing further transmission of drug-resistant M. tuberculosis strains. These findings emphasise the need for implementation of DST to SLDs in routine practice along with accurate and rapid molecular tests for the detection of FQ resistance mutations once MDR-TB is diagnosed.
Funding
This study was funded in part by the International Atomic Energy Agency under the RAF6040 project and the Regional Office for the Eastern Mediterranean/World Health Organization under the RPC/RAB&GH 10/11-03 project.
Competing interests
None declared.
Ethical approval
Not required.
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