INVITRO EVALUATION OF WIN-57273, A NEW BROAD-SPECTRUM FLUOROQUINOLONE

WIN 57273 is a new fluoroquinolone that has an expanded spectrum of activity against Staphylococcus spp. (MIC for 90% of isolates [MIC90], 0.008 μg/ml), Enterococcus faecalis (MIC90, 0.06 μg/ml), Bacillus spp. (MIC90, 0.03 μg/ml), Listeria monocytogenes (MIC90, 0.06 μg/ml), Streptococcus spp. (MIC90, 0.03 μg/ml), and Bacteroides fragilis group strains (MIC90, 0.5 μg/ml). Like other fluoroquinolone compounds, WIN 57273 was active against members of the family Enterobacteriaceae (97% of strains inhibited by ≤2 μg/ml), Haemophilus, Branhamella, and Neisseria strains (100% susceptible), Acinetobacter spp. (100% susceptible), and Pseudomonas aeruginosa (68% susceptible). We observed that WIN 57273 was very active against cephalosporin- or aminoglycoside-resistant gram-negative strains but shared cross-resistance with other fluoroquinolones. Increasing inoculum concentrations had minimal effects on WIN 57273 MICs, and the drug was considered to be bactericidal based on reference MBC and kill curve analyses. Unlike most previously studied drugs in this class, WIN 57273 had increased activity (three- to fourfold) at low pH. Rates of mutation to WIN 57273 resistance at eight times its MIC were in the range of 5.6 x 10-8 to >1.4 x 10-9. This new compound possesses a wide potential spectrum of use, and it should be evaluated further by in vitro and in vivo studies.