Occurrence of a novel class 1 integron harboring qnrVC4 in Salmonella Rissen

We described qnrVC4 in S. Rissen 166ANSS50, a swine isolate, which was detected in the study on quinolone resistance mechanisms of nontyphoidal Salmonella in Thailand. The isolate was found to harbor a 17-kb non conjugative plasmid carrying qnrVC4 within 8.91 kb of a novel In4-like class 1 integron (In805). It contained the multi-drug resistance gene cassettes of qnrVC4-qacH4-aacA4-cmlA7-bla(oxA-10)-aadA1-dfrA14 and unusual 3'-CS of mobC-IS6100. This 1014-bp qnrVC4 cassette included with promoter (P-qnrVC4: -35 TTGAGA and 10 TAGTCT) showed high homology with qnrVC4 in superintegron of V. cholerae 01 El Tor. The qnrVC4 recombinant plasmid resulted in 4-, 8-, and 16-fold increase in the MICs of nalidixic acid (2-8 mu g/mL), ciprofloxacin (0.015-0.125 mu g/mL), and norfloxacin (0.03-0.5 mu g/mL), respectively. In addition, the backbone plasmid revealed a novel replicon belonging to the MOBQ1 group from the broad-host-range mobilisable IncQ1 plasmid RES1010 based on relaxase sequences. This is the first known report of qnrVC in Salmonella enterica. The qnrVC4 gene was co-transferred with other resistance genes via a novel plasmid-borne In805. This allowed the spread of this resistance gene to Enterobacteriaceae. (C) 2017 Elsevier Inc. All rights reserved.