Investigation of Plasmid-Mediated Quinolone Resistance Determinants in Enterobacteriaceae: A Multicenter Study

Fluoroquinolones which are in use since 1986, are effective agents both against gram-positive and gram-negative bacteria. Quinolones show bactericidal effect as a result of inhibition of DNA gyrase and topoisomerase IV enzymes. Main quinolone resistance mechanisms are chromosomal mutations in these enzymes and decreased intracellular accumulation due to efflux pumps or decreased membrane uptake. Recently a new quinolone resistance mechanism mediated by plasmids has been defined. These plasmids carry genes called as qnr. Qnr genes do not cause quinolone resistance but they cause decreased quinolone susceptibility and lead to higher minimum inhibitory concentrations. Currently there are qnrA, qnrB, qnrC, qnrD and qnrS genes. This study was aimed to investigate the presence of plasmid-mediated quinolone resistance determinants in Enterobacteriaceae isolates collected from four different centers in Turkey. A total of 647 isolates (387 from Trabzon, Black Sea region; 82 from Canakkale, Trace region; 96 from Ankara, Central Anatolia region; 82 from Tokat, Black Sea region) belonging to the Enterobacteriaceae family collected between May-July 2009, were included in the study. Presence of qnrA, qnrB, qnrS and qnrC genes were investigated by multiplex polymerase chain reaction (PCR) method and confirmed by gene sequencing. The results of the PCR amplification revealed that 2 isolates were positive for qnrA, 12 isolates were positive for qnrB, 4 isolates were positive for qnrC and 10 isolates were positive for qnrS. However, the number of positive strains decreased with the use of gene sequencing, and this method led to the identification of qnrA1 in two isolates [Enterobacter cloacae (code. 796), Salmonella group B (code. 491)), qnrB1 in two isolates [Salmonella group B (code. 491), Citrobacter freundii (code. 768)], qnrB6 in one isolate [Escherichia coli (code. CC1800)], qnrB9 in one isolate [E.coli (code. CC1873)], qnr1324 in one isolate [Citrobacter koseri (code. MP5200)], qnrB27 in one isolate [C.freundii (code. 842)], qnrS1 in two isolates [E.coli (code. CC1705), E.coli (code.159)] and qnrB2 in one isolate [E.coli (code. 843)]. One of the isolates that carried the qnr gene was ciprofloxacin-resistant and two isolates were nalidixic-acid resistant. Transferable quinolone resistance due to the dissemination of qnr genes may have important impacts in terms of infection control and treatment problems. Survey of plasmid mediated quinolone resistance will help to determine the size of the issue and guide the measures that should be taken to avoid escalation of resistance and dissemination problem.