In vitro antibiotic susceptibilities of ocular isolates in North and South America. In Vitro Antibiotic Testing Group

Abstract

Purpose: To assess the in vitro susceptibility of ocular bacterial isolates from North and South America to antiinfectives that are commonly used in the treatment of external ocular infection.

Methods: Ocular isolates (n = 1,291) from 12 laboratories in the United States, Canada, Mexico, and Argentina were tested for their susceptibility to ofloxacin, ciprofloxacin, norfloxacin, gentamicin, tobramycin, chloramphenicol, tetracycline, and erythromycin using both disk-diffusion and broth-dilution methods.

Results: When the results from disk-diffusion and broth-dilution testing were combined, the relative overall in vitro efficacy was (in decreasing order): ofloxacin, ciprofloxacin, norfloxacin, gentamicin, chloramphenicol, tobramycin, tetracycline, and erythromycin. Against gram-positive organisms it was: ofloxacin, ciprofloxacin equivalent to chloramphenicol, norfloxacin, tetracycline, gentamicin, and erythromycin equivalent to tobramycin. Against gram-negative organisms it was: ofloxacin equivalent to ciprofloxacin and norfloxacin, gentamicin, tobramycin, chloramphenicol, and tetracycline comparable to erythromycin.

Conclusions: The fluoroquinolones ofloxacin, ciprofloxacin, and norfloxacin had higher overall in vitro efficacy than the other antibiotics tested. Of the fluoroquinolones, ofloxacin had the highest in vitro efficacy against gram-positive organisms. All three fluoroquinolones were equivalent in efficacy against gram-negative organisms.