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In vitro activity of novobiocin against multiresistant strains of Enterococcus faecium
P French1, E Venuti, H S Fraimow
1Dorrance H. Hamilton Laboratories, Department of Medicine, Jefferson Medical College, Philadelphia, Pennsylvania 19107.
Abstract:
Sixty strains of vancomycin- and ampicillin-resistant Enterococcus faecium were evaluated for their susceptibilities to novobiocin in vitro. In Mueller-Hinton broth, novobiocin inhibited all strains when it was used at a concentration of < or = 2 microgram/ml and 40 of 60 strains when it was used at a concentration of < or = 0.5 micrograms/ml. MICs were 8- to 16-fold higher in 50% serum. Novobiocin alone resulted in 2-log-unit killing at 24 h. Combinations of novobiocin and a fluoroquinolone (either ciprofloxacin or ofloxacin) were additive and bactericidal for quinolone-susceptible strains in either broth or 50% serum. Gentamicin did not affect novobiocin activity, and rifampin and doxycycline were antagonistic.