In vitro susceptibilities of bacterial ocular isolates to fluoroquinolones

Purpose. To evaluate and compare the in vitro antimicrobial activity of lev ofloxacin versus ciprofloxacin and ofloxacin against ocular isolates from p atients with bacterial conjunctivitis. Methods, The in vitro antimicrobial susceptibilities of ocular isolates to levofloxacin, ofloxacin, and ciprofl oxacin were determined using both the agar disk diffusion and broth dilutio n methods. Results. Disk diffusion susceptibility testing disclosed that 99 % (100 of 101 isolates) of Gram-negative isolates and 98% (127 of 129 isola tes) of Gram-positive isolates were susceptible to levofloxacin; 96% (97 of 101 isolates) of Gram-negative isolates and 78% (100 of 129 isolates) of G ram-positive isolates were susceptible to ofloxacin; and 94% (95 of 101 iso lates) of Gram-negative isolates and 61% (79 of 129 isolates) of Gram-posit ive isolates were susceptible to ciprofloxacin. Broth dilution testing disc losed that 99% (72 of 73 isolates) of Gram-negative isolates and 98% (111 o f 113 isolates) of Gram-positive isolates were susceptible to levofloxacin; 96% (70 of 73 isolates) of Gram-negative isolates and 92% (104 of 113 isol ates) of Gram-positive isolates were susceptible to ofloxacin; and 95% (69 of 73 isolates) of Gram-negative isolates and 82% (93 of 113 isolates) of G ram-positive isolates were susceptible to ciprofloxacin. Conclusions. In th is study, levofloxacin demonstrated superior in vitro activity against huma n bacterial conjunctival isolates compared with either ofloxacin or ciprofl oxacin (levofloxacin > ofloxacin > ciprofloxacin).