In Vitro Activity of Trovafloxacin against Bacteroides fragilis in Mixed Culture with either Escherichia coli or a Vancomycin- Resistant Strain of Enterococcus faecium Determined by an Anaerobic Time-Kill Technique

Abstract

To determine the efficacy of trovafloxacin as a possible treatment for intra-abdominal abscesses, we have developed an anaerobic time-kill technique using different inocula to study the in vitro killing of Bacteroides fragilis in pure culture or in mixed culture with either Escherichia coli or a vancomycin-resistant strain of Enterococcus faecium (VREF). With inocula of 5 ؋ 10 5 CFU/ml and trovafloxacin concentrations of <2 g/ml, a maximum observed effect (E max ) of >6.1 (log 10 CFU/ml) was attained with all pure and mixed cultures within 24 h. With inocula of 10 8 CFU/ml, a similar E max and a similar concentration to produce 50% of E max (EC 50 ) for B. fragilis were found in both pure cultures and mixed cultures with E. coli. However, to produce a similar killing of B. fragilis in the mixed cultures with VREF, a 14-fold increase in the concentration of trovafloxacin was required. A vancomycin-susceptible strain of E. faecium and a trovafloxacin-resistant strain of E. coli were also found to confer a similar "protective" effect on B. fragilis against the activity of trovafloxacin. Using inocula of 10 9 CFU/ml, the activity of trovafloxacin was retained for E. coli and B. fragilis and was negligible against VREF. We conclude that this is a useful technique to study the anaerobic killing of mixed cultures in vitro and may be of value in predicting the killing of mixed infections in vivo. The importance of using mixed cultures and not pure cultures is clearly shown by the difference in the killing of B. fragilis in the mixed cultures tested. Trovafloxacin will probably be ineffective in the treatment of infections involving large numbers of enterococci. However, due to its ability to retain activity against large cultures of B. fragilis and E. coli, trovafloxacin could be beneficial in the treatment of intra-abdominal abscesses.

Activity of moxifloxacin against Bacteroides fragilis and Escherichia coli in an in vitro pharmacokinetic/pharmacodynamic model employing pure and mixed cultures

“…The presence of the E. coli ATCC 25922 and VA 6886 strains reduced the killing activity of moxifloxacin against the B. fragilis strains investigated in the in vitro PK/PD model. This observation is supported by earlier results obtain with trovafloxacin (Stearne et al, 2001). Furthermore, protection of B. fragilis against the activity of metronidazole by Enterococcus faecalis has also been observed (Nagy & Földes, 1991).…”

“…Nagy & Földes (1991) reported that metronidazole was inactivated by a cell extract of E. faecalis. However, inactivation of trovafloxacin by Enterococcus faecium was not described (Stearne et al, 2001). antimicrobial agent.…”

“…ml À1 B. fragilis and approximately 3 3 10 7 c.f.u. ml À1 E. coli were used since abscesses contain a large number of bacteria (Stearne et al, 2001(Stearne et al, & 2002.…”

Effect of Recombinant Murine Granulocyte Colony-Stimulating Factor with or without Fluoroquinolone Therapy on Mixed-Infection Abscesses in Mice

“…Female specific-pathogen-free BALB/c mice (Charles River, Maastricht, The Netherlands) weighing 20 to 25 g were used throughout the study. The cecal contents of male specific-pathogen-free Swiss mice (Charles River) were used for the production of autoclaved cecal contents as preciously described (24). All animals received water and food ad libitum.…”

“…The MICs of trovafloxacin and moxifloxacin were determined using the standard broth microdilution method and inocula of 10 5 CFU/ml as previously described (24).…”