Transferable plasmid-mediated quinolone resistance in association with extended-spectrum β-lactamases and fluoroquinolone-acetylating aminoglycoside-6'-N-acetyltransferase in clinical isolates of Vibrio fluvialis

Vibrio fluvialis, which causes cholera-like diarrhoea in humans, is one of the aetiological agents of acute diarrhoea in Kolkata, India, and is resistant to many antimicrobial agents. Two V. fluvialis isolates resistant to fluoroquinolones and β-lactam antimicrobials were found to have mutations in the quinolone resistance-determining regions (QRDRs) of GyrA at position 83 and of ParC at position 85 as well as carrying a 150 kb plasmid harbouring the quinolone resistance gene qnrA1, the ciprofloxacin-modifying enzyme-encoding gene aac(6')-Ib-cr and genes encoding for extended-spectrum β-lactamases such as blaSHV and blaCTX-M-3. When this large plasmid was transferred to Escherichia coli by conjugation, the transconjugants showed a 10-75-fold increase in the minimum inhibitory concentrations of ciprofloxacin and norfloxacin. The qnrA1 gene was identified in a complex sul1-type integron in a plasmid of the transconjugants. Southern hybridisation and sequence analysis of qnrA1 and its flanking regions confirmed the presence of aac(6')-Ib-cr and blaCTX-M-3 but these were not associated with the sul1-type integron. Pulsed-field gel electrophoresis (PFGE) revealed that the two V. fluvialis isolates belonged to different clones. Although the presence of many qnr alleles has been reported amongst enteric bacteria in Asian countries, this is the first report on the emergence of qnrA1 in India. qnrA1 along with aac(6')-Ib-cr and blaCTX-M-3 genes on a mobile plasmid may spread to other bacterial species that are under the selective pressure of fluoroquinolones and β-lactam antimicrobials in this region