[Main pathogens and in vitro antimicrobial susceptibility in bacterial keratitis: 5-year study, 2005-2009]

To determine the most common pathogens involved in the etiology of bacterial keratitis at the Sorocaba Ophthalmological Hospital and the in vitro susceptibility of main antimicrobial used in the treatment of this pathology.

Retrospective study of all patients suspected of infectious keratitis that underwent microbiological exam at the Sorocaba Ophthalmological Hospital, between 2005 and 2009. To test susceptibility of antimicrobial drugs, antibiograms were made through the standard method of discs diffusion and interpretation following the National Committee on Clinical Laboratory Standards (NCCLS, Villanova, PA, USA).

963 samples were obtained in this period and 278 (28.86%) were positive for some pathogen. Among the positive for bacteria, the most common were Staphylococcus aureus (30.56%), Staphylococcus epidermidis (30.56%), Streptococcus sp (9.43%) and Pseudomonas sp (9.43%). Dividing in Gram's method, 191 (72.08%) were Gram-positive and 74 (27.92%) were Gram-negative. Analyzing in vitro antimicrobial effectiveness, the majority presented good susceptibility rates, beyond 85%, except cephalotin which presented 53.13%. At the same analysis, higher resistance rates with cephalotin (33.47%) and ciprofloxacin (11.36%) were noted.

Gram-positive bacteria were the most common pathogen isolated at microbiologic exams, especially staphylococci. despite the increasing number of isolated Gram-negative bacteria, meanly represented by Pseudomonas, related with the widespread use of contact lenses. Laboratorial exam revealed high sensibility values for most of antibiotics (more than 85%), except for cephalotin (53.13%). Higher resistance values were observed with cephalotin (33.47%) and ciprofloxacin (11.36%). With all these important variability of antibiotic susceptibility and pathogens involved in bacterial keratitis etiology, it is very important to know the specific characteristics of each infection for a better patient care.