Prevalence of qnr genes among extended-spectrum b-lactamase-producing enterobacterial isolates

Objectives: To evaluate the presence of qnr genes among enterobacterial isolates carrying extended-spectrum b-lactamases (ESBLs) in Barcelona, Spain. Methods: Screening for the qnrA, qnrB and qnrS genes was carried out by PCR amplification with specific primers in 305 non-duplicate, clinically relevant ESBL-producing enterobacterial isolates obtained from February 2003 to August 2004. ESBLs from all qnr-positive isolates were characterized by isoelectric focusing, PCR amplification and DNA sequencing. Plasmid analysis was performed by S1 digestion and hybridization with specific probes for the qnr and bla genes. Plasmids containing qnr genes were transferred by conjugation or transformation. The genetic environment of qnrA1 in selected isolates was characterized by cloning experiments. Results: Fifteen isolates, each from a different individual, carried qnr. Among them, 14 had qnrA1 (6 Klebsiella pneumoniae, 6 Enterobacter cloacae and 2 Escherichia coli isolates) and 1 had qnrS1 (K. pneumoniae). None of the isolates carried qnrB. Among the qnrA1-carrying isolates, 10 possessed both blaCTX-M-9 and blaSHV-12, 2 had both blaCTX-M-9 and blaSHV-92 and 2 had blaCTX-M-9 alone. The isolate with qnrS1 possessed blaSHV-12. The qnrA1 and ESBL genes were located together on plasmids ranging in size from 40 to 320 kb. qnrS1 and blaSHV-12 were not located on the same plasmid. Transfe