Fluoroquinolone resistance via qnrA integron cassette in ESBL producing Escherichia coli clinical isolates from Thailand

Abstract

Background:Although qnrA, encoding quinolone resistance protein, confers low-level resistance to fluoroquinolone, its role in quinolone resistance when associated with other resistant mechanisms remains unknown.Methods: One hundred extended-spectrum beta-lactamase (ESBL) producing Escherichia coli were collected from Siriraj Hospital (Bangkok, Thailand) and tested for qnrA by PCR. All qnrA positive isolates were investigated for gyrA mutations and a presence of class 1 integron by DNA sequencing and PCR. The locations of qnrA and intI1 genes were analyzed by Southern blot hybridization. Phenotypic characteristics were studied by antimicrobial susceptibility test and time kill method.Results: qnrA genes were found in 8% of ESBL-positive E. coli (8/100), confirmed to be qnrA1 by DNA sequencing. All qnrA1 positive isolates also harbored intI1 gene. Double mutations (S83L and D87N) in gyrA were found in 50% (4/8) of qnrA1 positive isolates. Specific qnrA1 and intI1 probes showed both qnrA1 and intI1 genes could be found on the chromosome and/or plasmids. Some isolates possessed two integron elements. The MIC (ciprofloxacin) against the isolate harboring both qnrA1 and gyrA with double mutations was 2-fold higher than that against the isolate with only gyrA, and was much higher than that against the isolate harboring only qnrA1 (MICs of 64 g/ml, 32 g/ml, and 0.12 g/ml, respectively). According to the time kill study, 0.5 g/ml of ciprofloxacin showed bactericidal activity after six hours of incubation against the isolate harboring only qnrA1. The bacteriostatic activity against the isolate harboring only gyrA with double mutations could be observed when the concentrations of ciprofloxacin were ≤256 g/ml. The regrowth of the isolate carried both genes in 64-128 g/ml at 24 hours of incubation were observed. Only 512 g/ml of ciprofloxacin showed bactericidal activity after four hours of incubation against the isolate harboring both qnrA1 and gyrA with double mutations.Conclusion: qnrA could integrate into the chromosome by class 1 integrons. Presence of fluoroquinolone resistance elements on both plasmid and chromosome indicated high selection pressure in E. coli and, may be, in other Gram-negative bacteria as well. The qnrA gene conferred higher-level ciprofloxacin resistance on double mutations in gyrA (S83L and D87N) background. http://dx.

Contribution of gyrA and qnrA genes in Ciprofloxacin Resistant Ecsherichia coli Isolates from Patients with Urinary Tract Infections of Imam Khomeini Hospital of Tehran

“…Also, simultaneous existence of qnrA gene and ESBLproducing genes were detected. However, the frequency of qnrA gene among E. coli isolates was 8 (25). In the current study, neither intl1 nor the ability of ESBL generation was investigated, yet, despite Winissorn's results, the frequency of qnrA gene among E. coli isolates in a recent study was higher (39% versus 8%).…”