Affiliation:
1. Department of Medical Microbiology and Infectious Diseases, Erasmus University Medical Center, Rotterdam, The Netherlands
Abstract
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 μg/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.
Publisher
American Society for Microbiology
Subject
Infectious Diseases,Pharmacology (medical),Pharmacology
Cited by
15 articles.
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