Efficacy of Fluoroquinolones on Methicillin-Resistant Staphylococcus aureus Strains Isolated from External Ocular Infections

Staphylococcus aureus is one of the most common causes of bacterial keratitis and conjunctivitis. This study was done to determine the efficacy of fluoroquinolones on Methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from external ocular infections.

This descriptive-analytical study was conducted on 187 pateiants (2 months to 61 years old) with symptoms of conjunctivitis and keratitis who were hospitalized or referred to the emergency department of hospitals in Golestan and Mazandaran provinces, Iran during 2020-22. The samples were taken from the external infection of the patients’ eyes. Methicillin-resistant Staphylococcus aureus isolates were identified by standard phenotypic microbiological and molecular detection (PCR) methods. The broth microdilution method determined sensitivity to quinolones and the minimum inhibitory concentration (MIC) in the 0.06-64 μg/ml range.

The frequency of ocular MRSA isolates (n=52) was significantly higher in spring, females and patients aged 1-30 years (P<0.05). Among the MRSA isolates causing conjunctivitis, the highest rates of resistance were observed against ciprofloxacin (n=18, 48.64%), enoxacin (n=17, 45.95 %), and ofloxacin (n=17, 45.95%). The MIC of gemifloxacin that inhibited the growth of 90% of MRSA isolates from conjunctivitis (MIC90=0.25 μg/ml) was 32-fold lower than that of ciprofloxacin.

Depending on the season and age, staphylococcus aureus may be the most common cause of bacterial conjunctivitis and keratitis. Considering the in vitro antibacterial potential of gemifloxacin, this antibiotic can be used to treat the bacterial external eye infections.