Multiple mechanisms contributing to ciprofloxacin resistance among Gram negative bacteria causing infections to cancer patients

Abstract

Fluoroquinolones prophylaxis (FQs) of bacterial infections in cancer patients have been long questioned for favoring the emergence of FQ resistance but with less emphasis on its impact on the mechanisms by which resistance develops. To elucidate FQs resistance mechanisms underlying ciprofloxacin resistance in Gram negative pathogens causing infections to cancer patients, 169 isolates were investigated. Broth microdilution assays showed high-level ciprofloxacin resistance in 89.3% of the isolates. Target site mutations were analyzed using Polymerase chain reaction (PCR) and DNA sequencing in 15 selected isolates. Of them, all had gyrA mutations (codons 83 and 87) with parC mutations (codons 80 and 87) in 93.3%. All isolates were screened for Plasmid-mediated quinolone resistance (PMQRs) genes using Polymerase chain reaction (PCR) that showed positive results in 56.8% of the isolates. Among PMQR genes, aac(6′)-Ib-cr predominated (42.6%) while qnr genes were harbored by 32.5%. This comprised qnrS in 26.6% and qnrB in 6.5%. Testing clonality of the qnr-positive isolates using Enterobacterial Repetit/ive Intergenic Consensus-PCR (ERIC-PCR) showed that most of them were not clonal. CIP MIC reduction by combining carbonyl-cyanide-m-chlorophenylhydrazone (CCCP), an efflux pump inhibitor, was tested among the isolates. Using a cut off value of a fourfold reduction, the contribution of efflux activity to FQs resistance was suspected in 18.3% of the isolates more frequently among non-fermenters (50.0%). Our results showed that most FQs resistance mechanisms are demonstrated among Gram-negative isolates causing infections to cancer patients. Target site mutations had the highest impact on CIP MIC compared to PMQRs and efflux activity.