In-vitro activity of trovafloxacin against sensitive and resistant aerobic bacteria using the standard microdilution broth method and Etest

A comparison of MICs of trovafloxacin (CP-99,219) determined by the standard microdilution broth method versus the Etest was performed for multiple strains of Gram-positive and Gram-negative bacteria. A comparison was also made of the in-vitro activity of trovafloxacin versus ciprofloxacin and ofloxacin. The MIC sub(50) and MIC sub(90) were determined by both methods for each species tested. The Etest resulted in MICs one to two dilutions higher than the microdilution broth method. Trovafloxacin was the most active agent against Gram-positive organisms. Ciprofloxacin was the most active agent against Citrobacter freundii, Proteus mirabilis, Proteus vulgaris, Morganella morganii and Serratia marcescens, while trovafloxacin had equal or greater activity compared with ciprofloxacin and ofloxacin against the other Gram-negative organisms tested. Overall, ofloxacin was the least active agent tested. In addition, the in-vitro activity of trovafloxacin or ciprofloxacin in combination with ampicillin/sulbactam, gentamicin or vancomycin was evaluated. The combination of trovafloxacin and gentamicin was synergic against two of 20 Enterococcus faecium isolates, the combination of trovafloxacin and ampicillin/sulbactam was synergic against two of 24 Enterococcus faecalis isolates, and the combination of ciprofloxacin and gentamicin was synergic against one of 25 Stenotrophomonas maltophilia isolates. All other antibiotic combinations resulted in an additive or indifferent effect.