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Antimicrobial Agents and Chemotherapy, Jun 1997, 1293-1297, Vol 41, No. 6
D Bahl, DA Miller, I Leviton, P Gialanella, MJ Wolin, W Liu, R Perkins and MH Miller
We characterized the effects of ciprofloxacin and rifampin alone and in
combination on Staphylococcus aureus in vitro. The effects of drug
combinations (e.g., indifferent, antagonistic, or additive interactions) on
growth inhibition were compared by disk approximation studies and by
determining the fractional inhibitory concentrations. Bactericidal effects
in log-phase bacteria and in nongrowing isolates were characterized by
time-kill methods. The effect of drug combinations was dependent upon
whether or not cells were growing and whether killing or growth inhibition
was the endpoint used to measure drug interaction. Despite bactericidal
antagonism in time-kill experiments, our in vitro studies suggest several
possible explanations for the observed benefits in patients treated with a
combination of ciprofloxacin and rifampin for deep-seated staphylococcal
infections. Notably, when growth inhibition rather than killing was used to
characterize drug interaction, indifference rather than antagonism was
observed. An additive bactericidal effect was observed in nongrowing
bacteria suspended in phosphate-buffered saline. While rifampin antagonized
the bactericidal effects of ciprofloxacin, ciprofloxacin did not antagonize
the bactericidal effects of rifampin. Each antimicrobial prevented the
emergence of subpopulations that were resistant to the other.
Copyright © 1997 by the American Society for Microbiology. All rights reserved.
In vitro activities of ciprofloxacin and rifampin alone and in combination against growing and nongrowing strains of methicillin- susceptible and methicillin-resistant Staphylococcus aureus
Department of Medicine, Albany Medical College, and Wadsworth Center for Laboratories and Research, New York 12208, USA.
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