Characterization of gyrA and gyrB mutations associated with fluoroquinolone resistance in Mycobacterium tuberculosis isolates from Morocco.

Objectives: Fluoroquinolones (FQs) are the cornerstone of treatment for drug-resistant tuberculosis (TB). They are the most effective second-line antimycobacterial drugs and are recommended for the treatment of multidrug-resistant TB (MDR-TB). However, it is widely accepted that FQ resistance is high among MDR-TB isolates. Thus, characterisation of mutations conferring resistance to FQs will be of a great interest for effective and efficient management of TB resistance in Morocco.

Methods: A laboratory collection of 30 Mycobacterium tuberculosis isolates previously characterised as phenotypically and genotypically MDR as well as 20 randomly selected pan-susceptible isolates were included in this retrospective study. The mutation profiles associated with resistance to FQs were assessed by PCR and DNA sequencing. Target sequences for two genes (gyrA and gyrB) were examined. All strains had their fingerprint previously established by spoligotyping.

Results: Molecular analyses showed that 30% of the MDR-TB isolates harboured FQ resistance mutations in gyrA, with the most prevalent being an alanine to threonine at position 90 (Ala90Thr) (56%; 5/9). None of the isolates harboured mutations in gyrB. All gyrA resistance mutant strains belonged to the LAM lineage, mostly LAM9, raising the possible emergence of a specific clone (gyrA mutant/LAM9).

Conclusion: The results of this preliminary study highlight the high prevalence of FQ resistance among MDR-TB isolates in Morocco and consequently the need for rapid detection of FQ resistance once MDR-TB is confirmed to adjust treatment in a timely manner and to interrupt the propagation of more severe forms of M. tuberculosis drug resistance.