Quinolone resistance via qnrA Integron cassette in Escherichia coli

Abstract

This study determined the characteristics of qnrA genes in Escherichia coli (E. coli) isolated from two hospitals in Bangkok, Thailand (one university hospital and one tertiary private hospital). Polymerase Chain Reaction (PCR) showed a presence of 8 qnrA positive isolates out of 100 extended-spectrum beta-lactamase (ESBL) producing E. coli isolated (quinolone resistant E. coli 83 isolates) from the university hospital, whereas no qnrA was detected in 90 quinolone resistant E. coli isolated from the tertiary private hospital. All qnrA positive isolates associated with the ESBL and class 1 integron (intI1). Double mutations in the quinolone resistance determining region (QRDR) in gyrA (resulted in S83L and D87N) were found in 4 out of 8 qnrA positive isolates. These 4 isolates were resistant to ciprofloxacin, while the isolates without double mutations were still susceptible to this drug. DNA sequencing analysis confirmed positive result for qnrA1. The result from Southern blot hybridization showed that qnrA genes were either located in the chromosome and/or large plasmids (3 out of 8 isolates). This indicated that the qnrA could be integrated into the chromosome via transposon elements along with class 1 integrons. The result of time kill study showed that the qnrA positive isolate indeed conferred low-level resistance to ciprofloxacin and norfloxacin, and they were able to show higher level of fluoroquinolone resistance and increasing the chance of regrowth only when associated with other resistant mechanisms, particularly the mutations in the QRDR (S83L and D87N).