title: 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 microg/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 microg/ml). Bactericidal activity measured in vitro after 1, 3, and 6 h of exposure to 0.5 microg/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 (log10 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.
authors.affiliation: Université Paris Diderot, EA3964, Paris, France.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Allou
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Cambau
authors.forename: Laurent
authors.initials: L
authors.lastname: Massias
authors.forename: Françoise
authors.initials: F
authors.lastname: Chau
authors.forename: Bruno
authors.initials: B
authors.lastname: Fantin
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000493:pharmacokinetics / Q000627:therapeutic use*; D002939:Ciprofloxacin / Q000493:pharmacokinetics / Q000627:therapeutic use*; D027081:DNA Gyrase / Q000235:genetics / Q000502:physiology; D004927:Escherichia coli Infections / Q000188:drug therapy* / Q000382:microbiology; D029968:Escherichia coli Proteins / Q000235:genetics / Q000502:physiology*; D005260:Female; D024841:Fluoroquinolones / Q000627:therapeutic use*; D051379:Mice; D008826:Microbial Sensitivity Tests; D014552:Urinary Tract Infections / Q000188:drug therapy* / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D024841:Fluoroquinolones; D002939:Ciprofloxacin; D027081:DNA Gyrase