Detection of qnrVC6, within a new genetic context, in an NDM-1-producing Citrobacter freundii clinical isolate from...

The objective of this study was to characterise the mechanisms underlying quinolone and oxyimino-cephalosporin resistance in a Citrobacter freundii clinical isolate obtained from the ICU in a university hospital in Uruguay.

Citrobacter freundii strain CF638 was isolated from a urine culture. Identification was performed using a VITEK^®2 system, and antimicrobial susceptibility was established by MIC determination and disk diffusion assay. Resistance genes and mobile genetic elements were identified by PCR and sequencing. Plasmid transfer was assessed by conjugation and the plasmid size was estimated by S1-PFGE. Plasmid incompatibility (Inc) group and toxin-antitoxin systems were sought by PCR.

Strain CF638 showed a multidrug-resistant profile, including resistance to carbapenems and quinolones. Transconjugant TcCF638, harbouring an ca. 200-kb IncA/C plasmid, also showed resistance to all β-lactams (except aztreonam) and diminished susceptibility to ciprofloxacin. PCR was positive for bla_NDM-1 and qnrVC in CF638 and TcCF638. Two different class 1 integrons were detected (In127 and In907). In127 featured the genetic array aadA2-ltr2. Conversely, complex In907 featured two variable regions (VRs); VR-1 consisted of aadB-bla_OXA-10-aadA1cc, whereas VR-2 featured a qnrVC6 gene 108bp downstream from ISCR1 and 45bp upstream from qacEΔ1. Expression of qnrVC6 was due to a putative promoter region, detected using the Neural Network Promoter Prediction program.

To the best of our knowledge, this constitutes the first report of qnrVC within a complex class 1 integron, as well as the first report of the occurrence of such a gene in an NDM-1-producing enterobacterial clinical isolate.