Involvement of topoisomerase mutations and qnr and aac(6')Ib-cr genes in conferring quinolone resistance to clinical isolates of Vibrio and Shigella spp. from Kolkata, India (1998-2009).

Objectives: Quinolone antibiotics have been widely used to treat diarrhoeal diseases caused by bacterial agents such as those belonging to the genera Vibrio and Shigella. As these pathogens are accumulating quinolone resistance, treating infections caused by them has become complicated.

Methods: In this study, Vibrio and Shigella spp. isolates obtained from diarrhoeal patients from Kolkata, India, over a period of 12 years (1998-2009) were analysed for quinolone resistance. A total of 27 Vibrio spp. (9 Vibrio cholerae, 11 Vibrio fluvialis and 7 Vibrio parahaemolyticus) and 10 Shigella spp. isolates (7 Shigella flexneri, 2 Shigella dysenteriae and 1 Shigella sonnei) showing reduced susceptibility to quinolones were studied to unravel the genetic factors responsible for quinolone resistance.

Results: Antimicrobial susceptibility testing showed a wide spectrum and varying degree of resistance to different generations of quinolones. Genotypic characterisation revealed the involvement of GyrA(S83I) and ParC(S85L) mutations in V. cholerae and V. fluvialis, whereas Shigella spp. isolates showed the mutations S83L and/or D87N/Y in GyrA and S80I or E84K in ParC. Analysis of plasmid-mediated quinolone resistance genes showed that qnrVC5 was detected in three V. fluvialis isolates, aac(6')-Ib-cr in one V. fluvialis isolate and qnrS1 in a S. flexneri isolate.

Conclusions: These results emphasise that quinolone resistance is widespread and therefore quinolones should be used prudently. To the best of our knowledge, this is the first study where resistance to various generations of quinolones in Vibrio and Shigella spp. has been examined in terms of detailed genotype-phenotype correlation.