Background: The public health burden related to N. gonorrhoeae infections is heightened by the high levels of resistance to previously used antimicrobials including fluoroquinolones. However, data on specific genetic events leading to ciprofloxacin resistance in Indian isolates is limited. This study was undertaken to investigate the mutations in gyrA and parC genes in isolates from across the country exhibiting a range of MICs to ciprofloxacin.
Methods: A total of 82 isolates (Delhi 64; Manipur 7; Srinagar 1; Madurai 5; Mumbai 5-centers of ICMR study) collected from STD patients during November 2010 to October, 2012 were studied. Antimicrobial susceptibility testing was done by disc-diffusion method and E test & results were interpreted as per CDS criteria. DNA sequence analysis of gyrA and parC gene was done as previously described. N. gonorrhoeae WHO F (ciprofloxacin-S) and K, M (ciprofloxacin-R) were used as controls.
Results: Out of 82 isolates tested, only 2 (2.4%) were susceptible to ciprofloxacin while 7 (8.5%) were less-susceptible & 73 (89%, 95% CI: 80.2% - 94.9%) were resistant (MIC ≥ 1µg/ml). Amongst these, 45 (61.6%, 95% CI: 49.5% – 72.8%) demonstrated high-level resistance, i.e., HLR (MIC ≥ 4 µg/ml). A S91F substitution in gyrA gene was demonstrated in all ciprofloxacin non-susceptible isolates. All resistant isolates demonstrated double mutations in gyrA gene. This was coupled with single mutation in parC gene in 20/28 (71.4%, 95% CI: 51.3% - 86.8%) with MIC 1-3 µg/ml and 43/45 (95.6%, 95% CI: 84.9% - 99.5%) of isolates with MIC ≥ 4 µg/ml. Double mutations in parC gene were observed in 2 isolates in MIC range of 1-3 µg/ml and 2 in MIC≥ 4 µg/ml. In addition, S87R mutation in parC gene was restricted only to HLR strains. One isolate (MIC 32 µg/ml) had a previously undescribed G85D substitution in the parC gene.
Conclusions: It was observed that the number of mutations in parC gene does not determine the level of ciprofloxacin resistance. Perhaps the efflux pump plays a significant role and warrants further investigation.