Purpose: Staphylococcus aureus is the predominant pathogen that causes keratitis, and the rate of occurrence of drug-resistant S. aureus is increasing. However, little is known about its clinical epidemiology in Japan. This study was designed to characterize the genotypes of methicillin-susceptible S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) isolates from keratitis and healthy conjunctival sacs.
Methods: Thirty keratitis isolates (19 MSSA and 11 MRSA) and 18 healthy conjunctival sac isolates (16 MSSA and 2 MRSA) obtained before cataract surgery were used. They were characterized by multilocus sequence typing. The prevalence of Panton–Valentine leukocidin was determined.
Results: In multilocus sequence typing analysis, ST5 and ST764 (ST5 variant) were the most frequently identified sequence types in MRSA strains from both keratitis and healthy conjunctival sacs. ST188 was the most frequently identified sequence type in the 19 MSSA isolates from keratitis (4 isolates, 21.1%), but was only identified in 1 of the 16 commensal MSSA strains. ST8 was found to be predominant among the 16 commensal MSSA strains (5 isolates, 31.3%). None of the isolates had Panton–Valentine leukocidin genes.
Conclusions: MRSA isolates from keratitis and healthy conjunctival sacs may have similar genotypic characteristics, but certain clones occur more often among MSSA isolates from keratitis than among commensal MSSA strains. These results suggest that specific MSSA lineages that possess genotypic characteristics can more effectively cause keratitis.