Impact of Low-Level Resistance to Fluoroquinolones Due to qnrA1 and qnrS1 Genes or a gyrA Mutation on Ciprofloxacin Bactericidal Activity in a Murine Model of Escherichia coli Urinary Tract Infection

Abstract

We investigated the impact of low-level resistance to fluoroquinolones on the bactericidal activity of ciprofloxacin in a murine model of urinary tract infection. The susceptible Escherichia coli strain CFT073 (ciprofloxacin MIC [CIP MIC] of 0.008 g/ml) was compared to its transconjugants harboring qnrA1 or qnrS1 and to an S83L gyrA mutant. The three derivatives showed similar low-level resistance to fluoroquinolones (CIP MICs, 0.25 to 0.5 g/ml). Bactericidal activity measured in vitro after 1, 3, and 6 h of exposure to 0.5 g/ml of ciprofloxacin was significantly lower for the derivative strains (P < 0.01). In the murine model of urinary tract infection (at least 45 mice inoculated per strain), mice were treated with a ciprofloxacin regimen of 2.5 mg/kg, given subcutaneously twice daily for 2 days. In mice infected with the susceptible strain, ciprofloxacin significantly decreased viable bacterial counts (log 10 CFU/g of tissue) in the bladder (4.2 ؎ 0.5 versus 5.5 ؎ 1.3; P ‫؍‬ 0.001) and in the kidney (3.6 ؎ 0.8 versus 5.0 ؎ 1.1; P ‫؍‬ 0.003) compared with those of untreated mice. In contrast, no significant decrease in viable bacterial counts was observed with any of the three derivative strains. The area under the concentration-time curve from 0 to 24 h/MIC and the maximum concentration of drug in serum/MIC ratios measured in plasma were indeed equal to 827 and 147, respectively, for the parental strain, and only 12.4 to 24.8 and 2.2 to 4.4, respectively, for the derivative strains. In conclusion, low-level resistance to fluoroquinolones conferred by a qnr gene is associated with decreased bactericidal activity of ciprofloxacin, similar to that obtained with a gyrA mutation.Urinary tract infection (UTI) due to Escherichia coli is the most common bacterial infection. Fluoroquinolones are commonly used for the treatment of UTI because isolated microorganisms are frequently resistant to aminopenicillins and trimethoprim-sulfamethoxazole (22), and fluoroquinolones are given orally. However, resistance to fluoroquinolones in E. coli has increased due to their large use (13, 23). Classical mechanisms of quinolone resistance are due to chromosomal mutations in the genes encoding their targets (quinolone resistance-determining regions of the type II topoisomerases) or in regulatory genes affecting permeability or efflux (15, 29). More recently, plasmid-mediated mechanisms were reported, such as those due to qnr genes (16, 25) encoding pentapeptide repeat proteins, aac(6Ј)-Ib-cr encoding a modified acetyltransferase (32), and qepA encoding an active efflux pump (27). The Qnr proteins protect DNA gyrase from quinolone inhibition.Enterobacteriaceae with plasmid-mediated resistance to fluoroquinolones due to qnrA, qnrB, or qnrS have been described worldwide (31) and particularly among E. coli from UTI (5, 39). Acquisition of qnr genes increases fluoroquinolone MICs by between 8-and 64-fold; however, the final MICs remain below the susceptibility breakpoints, according to CLSI (1 g/ ml) (6) and to the European Committee o...

Contribution of QnrA, a Plasmid-Mediated Quinolone Resistance Peptide, to Survival of <i>Escherichia coli</i> Exposed to a Lethal Ciprofloxacin Concentration

“…These results suggested that the contribution of qnrA to bacterial survival is not equivalent in all serotypes of E. coli strains. To date, some investigators have reported that in the present of CIP, E. coli isolates with qnr could survive longer than those without qnr (13,21). In the present study, we also confirmed that the acquisition of qnrA contributed to increased bacterial survival under exposure to lethal CIP concentrations in E. coli strains displaying certain O-serotypes (O1, O6, and O25b).…”

“…To date, 6 groups of Qnr proteins have been identified (QnrA, QnrB, QnrC, QnrD, QnrS, and QnrVC) (11,12). Allou et al evaluated the impact of the acquisition of genes encoding Qnrs, and found that the low-level resistance to FQs conferred by these genes was associated with decreased bactericidal activity of CIP (13). In a preliminary study, we also found that qnrA contributed to improved bacterial survival at lethal CIP concentrations.…”

“…At present, the qnr are rapidly spreading among Family Enterobacteriaceae. Although no significant difference have been observed in the clinical outcomes of serious infections, such as those of the bloodstream, between qnr-positive and qnr-negative groups (26), some investigators have reported that the presence of qnr determinants reduced the efficacy of CIP in animal models of pneumonia and urinary tract infections (27)(28)(29). Therefore, further investigation is necessary to elucidate the impact of low-level resistance to FQs due to acquisition of qnr.…”

Antibacterial resistance pattern among Escherichia coli strains isolated from Mansoura hospitals in Egypt with a special reference to quinolones

“…Six variants have been identified (qnrA1 to qnrA6). These genes can increase the MIC of fluoroquinolones up to 32-fold in E. coli isolates (Poirel et al, 2006;Allou et al, 2009). In addition, qnrA gene enhances the selection of chromosomal encoded quinolone resistance determinants which confer additional resistance to fluoroquinolones.…”

“…Fluroquinolones act by increasing levels of enzyme-mediated DNA cleavage affecting DNA gyrase enzyme which catalyzes the negative supercoiling of DNA and topoisomerase IV enzyme which decatenates or removes the interlinking of daughter chromosomes at the completion of a round of DNA replication allowing their segregation into daughter cell (Ambrozic et al, 2007;Wang et al, 2009). Quinolone resistance has traditionally been attributed mainly to chromosomal mutations in the gyrA and gyrB genes of DNA gyrase and in parC and parE genes of topoisomerase IV or due to decreased intracellular concentration as a result of decreased permea-bility of the membrane or over expression of efflux pump systems (Poirel et al, 2006;Oktem et al, 2008;Allou et al, 2009).…”