Alterations in ocular pathogen susceptibility to gentamicin and tobramycin

Purpose: To evaluate and compare the “in vitro” susceptibility of ocular bacterial isolates to aminoglycoside antibiotics (gentamicin and tobramycin) and to analyze the alteration in susceptibility after 14 years of introduction of tobramycin in Brazilian ophthalmic practice. Methods: The results of antibiotic susceptibility tests in a period of three years with 887 bacterial strains (Study “A”) were retrospectively analyzed and then compared with the results obtained fourteen years ago with 124 microorganisms (Study “B”), when tobramycin was first tested in Brazil for isolated eye strains. In both studies, the data analyzed were from the files of the Ocular Microbiology Laboratory of the Federal University of São Paulo. Results: The “in vitro” effectiveness of both antibiotics regarding the total number of positive isolates was significantly higher for tobramycin in both studies. An increase in the Staphylococcus aureus strains resistant to tobramycin and only a decreasing trend in the number of microorganisms resistant to gentamicin was observed. With Pseudomonas sp, a strong tendency to the increase of susceptibility to gentamicin and to the appearance of strains resistant to tobramycin occurred. Conclusions: The introduction of tobramycin in the treatment of ocular infections and the possible decrease in number of gentamicin prescriptions during the last fourteen years might be the cause of modifications in the susceptibility observed in the total of positive isolates mainly Staphylococcus aureus and Pseudomonas sp. For the isolated microorganisms from the conjunctiva, the sensitivity to both antibiotics was equivalent. Alterações na sensibilidade dos patógenos oculares à gentamicina e à tobramicina