Accumulation of garenoxacin by Bacteroides fragilis compared with that of five fluoroquinolones

Objectives: Garenoxacin is a novel des-F(6)-quinolone with good anti-anaerobe activity. The accumulation of garenoxacin and five other quinolones in the presence and absence of a variety of efflux pump inhibitors, including carbonyl cyanide m-chlorophenyl hydrazone (CCCP: 100 µM), verapamil (25 µM), reserpine (20 mg/L), sodium orthovanadate (50 µM) and Phe-Arg-β-naphthylamide (MC-207110) (20 mg/L) was investigated.

Methods: Bacteroides fragilis was grown in Wilkins Chalgren broth (Oxoid Ltd, UK) in a MKII anaerobic workstation (Don Whitley, Shipley, UK). Susceptibility testing was performed, according to the agar doubling dilution method, using Wilkins Chalgren agar supplemented with 5% horse blood. A fluorometric assay was used to measure the accumulation of quinolones (10 mg/L) by B. fragilis.

Results: The activity of the agents for B. fragilis NCTC 9343/ATCC 25285 was clinafloxacin > garenoxacin > levofloxacin = gatifloxacin > moxifloxacin > ciprofloxacin. A weak correlation was observed between the molecular size of the free form and the MIC, the steady state concentration (SSC) and the initial rate of accumulation, but not for the hydrophobicity of each agent. In the presence of reserpine, the SSC of all agents increased. The addition of CCCP had no effect upon garenoxacin or clinafloxacin accumulation, but significantly increased the SSC of ciprofloxacin, moxifloxacin, gatifloxacin and levofloxacin. Verapamil increased the SSC of garenoxacin, whereas sodium orthovanadate had no effect on the concentration of accumulated garenoxacin.

Conclusions: These data suggest that there is probably more than one type of efflux pump in B. fragilis that exports quinolones.