After reviewing the microbiology records of all corneal scrapings with a diagnosis of infectious keratitis, researchers in Iran recently reported the spectrum and trends of isolated microorganisms and their antibiotic susceptibility profile. Pseudomonas aeruginosa was found to be the most common causative agent in patients with keratitis, although Streptococcus pneumonia was the most prevalently isolated microorganism in patients older than 50.

The researchers performed 6,282 corneal scrapings during the study period, of which 39.5% were culture-positive. They noted that Fusarium sp. was the most common pathogen in patients with fungal keratitis. The prevalence of bacterial keratitis due to gram-positive microorganisms increased over time; however, the number of Pseudomonas keratitis cases decreased in the second half of the study.

Regarding antibiotic susceptibility, gram-negative organisms showed a good sensitivity to levofloxacin, while 34.1% of Staphylococcus aureus isolates and 29.7% of coagulase-negative staphylococci were resistant. The study determined that the odds of ciprofloxacin and levofloxacin resistance increased 1.25 and 1.15 for each one-year increase in culture date, respectively.

“Levofloxacin monotherapy might still be a good option in patients with gram-negative bacterial keratitis,” the researchers concluded. “However, owing to increasing resistance of staphylococci to fluoroquinolones, a regimen that consists of a combination of fortified antibiotics may be more effective in staphylococcal keratitis.”