Objective: The aims of this study are to detect the quinolone resistance rates among Escherichia coli and Klebsiella pneumoniae spp. isolates in our region and to investigate the most common quinolone resistance mechanisms.

Material and Methods: The presence of qnrA, qnrB, qnrS, aac(6’)-Ib, gyrA and parC genes were investigated by polymerase chain reaction method in 265 Escherichia coli, 33 Klebsiella pneumoniae and two Klebsiella oxytoca strains which were isolated between February–August 2009, and found to be non/intermediate susceptible to nalidixic acid . Sequence analysis was used for detection of gyrA and parC mutations.

Results: Resistance to nalidixic acid was determined as 52% for E. coli and 27.5% for Klebsiella spp. Beta-lactam, aminoglycoside, trimethoprim-sulfamethoxazole resistance and ESBL-production rates were significantly higher among nalidixic acid resistant isolates. Double mutations were detected in gyrA quinolone resistance defining region (Ala67-Gln106); the first one being Ser83Leu in all isolates and the other being Asp87Tyr in one isolate and Asp87Asn in other isolates. Ser80Ile alteration was observed among all isolates sequenced for parC mutations; while 32 (40.3%) of the isolates had an additional mutation, as Glu84Val, Glu84Gly and Glu84Ala in 26, four and two, respectively. The aac(6’)-Ib gene was detected in 99 (37.4%) of E. coli and four (12.1%) of K. pneumoniae isolates. The qnr gene was not detected in any of the tested isolates.

Conclusion: The quinolone resistance rates and accompanying ESBL-production was high among the isolates in our region. We have detected three or more mutations in gyrA and parC regions in quinolone resistant isolates, and additional aac(6’)- Ib gene in a significant number of isolates. The qnr gene was not detected in any of the tested isolates.