Objective: To evaluate the in vitro activity of
gatifloxacin. Methods:The MICs of gatifloxacin against 1 192 clinical
isolates were determined and compared with other antimicrobial agents using agar dilution method. The bactericidal activity and factors influence the activity of
gatifloxacin were investigated. Results:The results showed that gatifloxacin had broad spectrum activity. It was highly active against MSSA, S.
pneumoniae, Hemolytic streptococcus, H. influenzae, MIC 90 ≤0.25 mg/L, but it was poorly active against methicillin resistant Staphylococci (MRS) and Enterococci. The MIC 90 ≤2 mg/L for K.pneumoniae, Serratia spp ., P.vulgaris, Salmonellae spp. and Shigellae spp., however, it was less active against E.coli . Gatifloxacin also had good activity against P.aeruginosa and S.maltophilia, but poorly active against Acinetobacter spp..It was highly active against anaerobes, including B.fragilis, Peptostreptococcus spp.. Gatifloxacin was obviously more active against MSSA, S.pneumoniae, Hemolytic Streptococcus and B.fragilis than ciprofloxacin and ofloxacin. The activity of gatifloxacin against strains of Enterobacteriaceae and nonfermentative Gram negative organisms was better than or comparable to that of ciprofloxacin. Gatifloxacin is a bactericidal agent with rapid killing activity . Inoculum size of bacteria and concentration of human serum in test media did not influence, while pH of media slightly influence the in vitro activity of gatifloxacin. Conclusions:Gatifloxacin is a broad spectrum agent, it is highly active against most organisms especially the pathogens of community acquired respiratory tract infections. Our findings suggest gatifloxacin could be a promising agent for the treatment of infections caused by sensitive organisms.