The Intracellular Concentrations of Fluoroquinolones Determined the Antibiotic Resistance Response of Escherichia Coli

Abstract

The extensive consumption of antibiotics has been reported to significantly promote the generation of antibiotic resistance (ABR), however, a quantitative relationship between antibiotic exposure and ABR response is absent. This study aimed to pinpoint the accurate regulatory concentration of antibiotics and to understand the biochemical mechanism of the mutual action between antibiotic exposure and ABR response. Highly sensitive analytical methods were developed by using UPLC-MS/MS to determine the total residual, extracellular residual, total intracellular, intracellular residual and intracellular degraded concentrations of three representative fluoroquinolones (FQs), including ciprofloxacin (CIP), ofloxacin (OFL) and norfloxacin (NOR), with detection limits in the range of 0.002–0.057 μg/L, and recoveries in the range of 80–93%. The MICs of Escherichia coli (E. coli) were 7.0–31.4 fold of the respective MIC0 after 40-day FQ exposure, and significant negative associations were discovered between the intracellular (residual, degraded or the sum) FQ concentrations and ABR. Reduced membrane permeability and enhanced multi-drug efflux pumps contributed to the decreasing intracellular concentration. These results unveiled the pivotal role of intracellular concentration in triggering ABR, providing important information to understand the dose-response relationship between antibiotic exposure and ABR response, and ascertain the target dose metric for eliminating ABR crisis.

Keywords: Fluoroquinolones, Antibiotic resistance, Dose-response relationship, Liquid chromatography-tandem mass spectrometry, Environmental concentration