Genotypic detection of fluoroquinolone resistance in drug-resistant Mycobacterium tuberculosis at a tertiary care centre in south Coastal Karnataka, India

Objectives: This study aimed to characterise mutations associated with fluoroquinolone resistance in drug-resistant Mycobacterium tuberculosis clinical isolates at a tertiary care centre in south Coastal Karnataka, India. Methods: DNA from 50 M. tuberculosis clinical isolates was extracted and the gyrA and gyrB genes were amplified. Purified amplicons of gyrA and gyrB were sequenced and extended-sequencing PCR products were analysed. Analysis of mutations in gyrA and gyrB was done using the MUBII-TB-DB database. Statistical analysis was performed using SPSS v.22 and data were compared by χ² test. A P-value of <0.05 was considered statistically significant. Results: Mutations conferring resistance to fluoroquinolones were observed in 9 isolates (18%). The gyrA A281G (D94G) mutation was observed in 3 isolates (6%), whereas mutations G280T (D94Y) and A281C (D94A) were each observed in 1 isolate (2%). Mutation G1498A (D500N) in gyrB alone was observed in 2 isolates (4%). Two isolates (4%) had mutations both in gyrA and gyrB; gyrA mutation T271C (S91P) was observed in one isolate, whereas the other isolate had gyrA C269G (A90G), but both isolates had a common G1498A (D500N) gyrB mutation. G284C mutation conferring S95T polymorphism (not associated with fluoroquinolone resistance) was observed in 39/50 isolates (78%). Conclusion: gyrA mutations at codons 94, 91 and 90 and gyrB mutation G1498A (D500N) were the most common mutations associated with fluoroquinolone resistance in clinical isolates in this study. Future studies including a larger number of samples are desirable to fully explore the true extent of fluoroquinolone resistance and mutations associated with them.