The antibacterial spectrum of besifloxacin, a novel fluoroquinolone recently approved for treatment of ocular infections, was studied using 2,690 clinical isolates representing 40 species. Overall, besifloxacin was the most potent agent tested against gram-positive pathogens and anaerobes and was generally equivalent to comparator fluoroquinolones in activity against most gram-negative pathogens. Besifloxacin demonstrated potent, broad-spectrum activity, which was particularly notable against gram-positive and gram-negative isolates that were resistant to other fluoroquinolones and classes of antibacterial agents.Bacterial conjunctivitis is an inflammation of the transparent mucous membrane covering the globe of the eye. This common ocular surface infection is caused by a broad variety of bacteria and is usually treated with broad-spectrum topical ophthalmic antibacterials (1,13,19,20). The increasing prevalence of drug-resistant ocular isolates highlights the need for the development of new agents for the treatment of bacterial infections (8). Besifloxacin ( Fig. 1) is a novel 8-chloro-fluoroquinolone agent with potent, bactericidal activity against prevalent and drug-resistant pathogens (6). Clinical development of the agent for use as a topical ophthalmic agent has been completed, and the agent has demonstrated consistent safety and efficacy in three bacterial conjunctivitis clinical trials (14,16,21). Pharmacokinetic studies demonstrated that after a single topical dose of 0.6% besifloxacin ophthalmic suspension, mean besifloxacin levels in human tears ranged from 610 g/ml at 10 min postadministration to 1.6 g/ml at 24 h postadministration (12). Here, the in vitro activity of besifloxacin against a broad range of aerobic and anaerobic bacterial species, including problematic drug-resistant strains, was evaluated.Totals of 2,535 aerobic and 155 anaerobic bacterial clinical isolates from Eurofins Medinet (Chantilly, VA) were selected for the study. The majority of isolates were from 2005 to 2008, and wherever possible, isolates were from ocular and respiratory specimens of U.S. origin. Susceptibility testing was conducted per Clinical and Laboratory Standards Institute reference methods (9-11).Activity of besifloxacin against gram-positive aerobes. Against Enterococcus faecalis and E. faecium, including vancomycin-resistant enterococci, besifloxacin was more potent than the comparator fluoroquinolones, as well as azithromycin, vancomycin, and tobramycin (Table 1). Besifloxacin further demonstrated excellent activity against Listeria monocytogenes, similar to that of tobramycin and penicillin and better than that observed with comparator fluoroquinolones.For Staphylococcus aureus and S. epidermidis, previously reported MIC 50 s/MIC 90 s were consistent with current besifloxacin values for quinolone-susceptible and quinolone-resistant subsets (3,5,14). Besifloxacin was especially potent against ciprofloxacin-resistant isolates; for example, the MIC 90 s for non-ciprofloxacin-susceptible S. aureus were 4 g/ml for...
