QnrB9 in Association with TEM-116 Extended-Spectrum Beta-Lactamase in Citrobacter freundii Isolated from Sewage Effluent: First Report from Italy

The aim of the present study was to investigate the mechanism of quinolone and beta-lactam resistance in an isolate of Citrobacter freundii PC2/08 collected from sewage effluent from L'Aquila, Italy. qnrB-9 and bla(TEM-116) were co-expressed in a large plasmid identified in C. freundi PC2/08 strain. Compared to TEM-1, TEM-116 showed two single mutations: V84I and A184V. The pIPC2/08 plasmid conferred resistance to several beta-lactams and fluoroquinolones. Tazobactam could be considered a good inhibitor whereas clavulanic acid was unable to restore susceptibility to amoxicillin. The QnrB-9 element seems to confer the same level of resistance to levofloxacin and ciprofloxacin with minimum inhibitory concentration (MIC) values of 4 mg/L for either. In this study, we confirm the common association of plasmid-mediated quinolone resistance with extended-spectrum beta-lactamase (ES beta L) production. This is the first finding in Italy of qnrB9 and TEM-116 in a non-clinical or animal strain.