In vitro activities of levofloxacin, gatifloxacin, moxifloxacin and garenoxacin against Bacteroides fragilis strains evaluated by kill kinetics

Abstract

This study was designed to investigate the killing activity of levofloxacin, gatifloxacin, moxifloxacin and garenoxacin against 12 Bacteroides fragilis strains by kill kinetics over time. MIC values were determined by Etest and by agar dilution. B. fragilis strains were divided according to their MIC values into two groups: one group with strains with MIC ,8.0 mg ml "1 and one group with strains with MIC ¢8.0 mg ml "1 . For kill kinetics over time, the strains with MIC ,8.0 mg ml "1 were incubated with the antibiotics at 0.5, 1, 2 and 4 times their MIC values. The strains with MIC ¢8.0 mg ml "1 were incubated with 0.5, 1, 2, and 4 times the maximum achievable concentrations of the antibiotics in human plasma (C max ). Among the strains with MIC ,8.0 mg ml "1 levofloxacin and gatifloxacin showed equal efficacy. The growth of the strains with MIC ¢8.0 mg ml "1 was barely affected by levofloxacin, while gatifloxacin had bactericidal action when concentrations of 4¾C max were used. Moxifloxacin was more effective against both groups of strains compared with levofloxacin and gatifloxacin. Garenoxacin was the most active agent against all strains investigated. Due to the varying in vitro activity of the quinolones against obligate anaerobes the treatment with quinolones of patients with intra-abdominal infections needs intensive scrutiny. INTRODUCTIONBacteroides fragilis is the most commonly isolated anaerobic pathogen (Wexler, 2007 2006). However, the problem of increasing resistance rates also applies to quinolones. Golan et al. (2003) found that quinolone resistance has been increasing among Bacteroides since 1994. Recently, Nagy et al. (2011) reported a dramatic increase in resistance to cefoxitin, clindamycin and moxifloxacin, with resistance rates of 17.2 %, 32.4 % and 13.6 %, respectively, throughout Europe, with higher resistance rates for moxifloxacin in Scandinavian countries than in Mediterranean countries (Fille et al., 2006;Hedberg et al., 2003). Thus, the knowledge of resistance patterns is important for adequate prophylaxis and treatment of anaerobic or mixed aerobic and anaerobic infections. As studies employing kill kinetics are expensive in terms of time and cost, they are not likely to be performed in the routine laboratory. Therefore, the aim of the present study was to investigate the in vitro killing activity of four different quinolones against 12 B. fragilis strains evaluated by kill kinetics over time. METHODSBacterial strains. Twelve B. fragilis isolates were selected from the institute's stock. The RMA strains were kindly provided by E. J. C. Goldstein, R. M. Alden Research Lab, Culver City, California, USA.3These authors contributed equally to this work. The WAL strains were collected at the University Hospital of Wales, Cardiff, UK, and are isolates of an international anaerobe study tested

Activity of the investigational fluoroquinolone finafloxacin and seven other antimicrobial agents against 114 obligately anaerobic bacteria

“…[11,[20][21][22]. At neutral pH, finafloxacin showed activity against the anaerobic bacteria tested similar to that of moxifloxacin.…”