[In vitro fluoroquinolone resistance in ocular bacterial isolates]

To assess the in vitro resistance of ocular bacterial isolates to fluoroquinolone that are commonly used in the treatment of ocular infection.

Ocular bacterial isolates (n = 347) from Beijing Institute of Ophthalmology were tested for their resistance to ofloxacin, ciprofloxacin and norfloxacin. In vitro susceptibility testing was determined by the Kirby-Bauer disk diffusion method.

The total number of ocular bacterial isolates was 347 from January, 1999 to December, 2000 including gram-positive cocci 192 (55.3%), gram-negative cocci 16 (4.6%), gram-positive bacilli 44 (12.7%), gram-negative bacilli 89 (25.7%), Nocardia 6 (1.7%). The percentage of resistance in total ocular bacterial isolates to ofloxacin, ciprofloxacin and norfloxacin was 28.5%, 25.9% and 34.9% respectively. The resistance of streptococcus species to ofloxacin (5.9%) and ciproloxacin (11.8%) was significantly lower than gentamycin (52.9%) and tobramycin (70.6%) (P < 0.01), and to norfloxacin (23.5%) was significantly lower than tobramycin (P < 0.01). Pseudomonas showed significantly lower resistance to ciprofloxacin (6%) ofloxacin (14.0%) and norfloxacin (14.0%) than gentamycin (42.0%) (P < 0.01 and P < 0.05). The percentage of resistance in staphylococcus species to norfloxacin (46.8%) was higher than gentamycin (30.8%) and tobramycin (27.6%) (P < 0.05 and P < 0.01 separately). The resistance of gram-positive bacilli to ofloxacin, ciproloxacin and norfloxacin. was equivalent (P > 0.05).

The fluoroquinolones, ofloxacin and ciprofloxacin have higher overall in vitro efficacy on most of the ocular bacteria than gentamycin and tobramycin, but ofloxacin and ciprofloxacin are equivalent to gentamycin and tobramycin in efficacy against staphylococcus species.