Shifting trends in in vitro antibiotic susceptibilities for common ocular isolates during a period of 15 years

PURPOSE: To assess the in vitro susceptibility of the most common ocular bacterial isolates to several antibiotics and verify changing trends in the antibiotic suscep tibility in a 15-year period. DESIGN: Experimental study. METHODS: All cultures positive for Staphylococcus aureus, coagulase-negative Staphylococcus (CNS), Streptococ cus sp, and Pseudomonas sp in conjunctival (n = 4,585) and corneal (n = 3,779) samples from patients seen at the Federal University of Sao Paulo from 1985 to 2000 were evaluated. Cultures were performed in liquid and solid media, and susceptibility tests were done to amikacin, gentamicin, neomycin, tobramycin, ciprofloxacin, norfloxacin, ofloxacin, cephalothin, and chloramphenicol. RESULTS: Amikacin and neomycin showed an improvement of their sensitivity during the study period (88%-95% and 50%-85%, respectively) for corneal and conjunctival samples. Gentamicin and tobramycin revealed a decrease of sensitivity in time, from 95% to less than 80% in corneal and conjunctival samples. Ciprofloxacin, norfloxacin, and ofloxacin had good sensitivity to all evaluated bacteria, better in conjunctiva (95%) than in cornea (90%). Sensitivity of S. aureus to cephalothin decreased during the study but was still 98% for CNS. Chloramphenicol had good sensitivity to S. aureus (85% in corneal and 92%in conjunctival same ples), CNS (87% and 88.5%), and Streptococcus sp (95% and 96%). CONCLUSIONS: Gentamicin, tobramycin, and cephalothin decreased their in vitro susceptibility to all tested pathogens. The fluoroquinolones remained a good choice in the treatment of ocular infections, with high suscep, tibility to all pathogens tested. Chloramphenicol also revealed an increase in its susceptibility to all bacteria evaluated.