Shifting trends in bacterial keratitis in a referral center

The purpose of this study is to analyze the microbiological profile of bacterial keratitis, the antibiotic susceptibility of bacterial isolates and identify seasonal variations over an 11-year period.

Charts of patients who were diagnosed with bacterial keratitis and underwent corneal scraping between January 1, 2009 and December 31, 2019 at a tertiary referral center in Türkiye were retrospectively evaluated. Demographic factors, culture positivity rate, microbiological profiles of bacterial keratitis, antibiotic susceptibilities and seasonal variation were analyzed. Antimicrobial susceptibility testing was performed using the automated system Phoenix 100TM (Becton Dickinson, USA), together with the disk diffusion method according to the EUCAST rules.

Of a total of 389 corneal scrapes, culture positivity was observed in 142 with a total of 152 bacterial organisms that grew (73.7% Gram positive and 26.3% Gram negative). The most frequently isolated pathogen is coagulase-negative staphylococcus (32.2%). All Gram-positive bacteria were 100% sensitive to vancomycin and cefazolin. This was followed by moxifloxacin with 97.8% and gentamicin with 96.6%. The sensitivity of fusidic acid was lowest with 61.3%. All Gram-negative bacteria were sensitive to amikacin. Sensitivity was also 96.0% to gentamicin and 90.5% to ceftazidime. Fluoroquinolone sensitivity was 89.7%. During the 11-year period, the percentage of Gram-positive isolates decreased over time, while an increase in the percentage of Gram-negative isolates was observed. A significant seasonal shift was observed, with bacterial keratitis cases increasing in autumn and summer months, correlating with a rise in Gram-negative infections.

Instead of more potent antibiotics such as vancomycin and ceftazidime, high-susceptibility 4th generation quinolones such as moxifloxacin and levofloxacin, cefazolin, amikacin and gentamicin may be preferred for empirical treatment. A temporal trend indicating an increasing Gram-negative organisms prevalence was observed.