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I. Behlau, S. R. Heimer, E. M. Leonard, J. N. Martin, C. H. Dohlman, M. S. Gilmore; Staphylococcus Aureus-associated Keratitis: Phenotypic and Genotypic Characterization. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5113.
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© ARVO (1962-2015); The Authors (2016-present)
S. aureus is a normal commensal of the human skin and nasopharynx, yet S. aureus infection appears to be predominantly caused by only a subset of these organisms. This is an epidemiologic analysis of the phenotypic and genotypic characteristics of S.aureus clinical isolates that have been associated with keratitis.
All S. aureus clinical isolates were prospectively collected over a 24 month period at the MEEI (2006-2008). The diagnosis of clinical keratitis and associated risk factors was by medical record review. The S. aureus-associated keratitis strains were assessed for: 1) antibiotic susceptibility data by CLSI standards, 2) biofilm robustness by Gentian violet staining using an in vitro microtiter plate assay, and 3) species lineage by multi-locus sequence typing (MLST).
26 cases of keratitis were identified from the 600 S. aureus clinical isolates. Risk factors associated with S.aureus keratitis included trauma, prior surgery, soft contact lens wear, and the presence of a foreign body. Ocular surface disease does not appear to be an independent risk factor. All 26 isolates were tetracycline- and trimethoprim-sulfamethoxazole- sensitive. Prior antibiotic usage did correlate strongly with methicillin-resistance (9/26 strains), and all the MRSA strains were found to be ciprofloxacin-resistant (10/26). More than one-third of all the S.aureus keratitis-associated isolates, and more than one-half of medically-related foreign body infections, were caused by a single clone, ST5. Both sensitive and resistant S. aureus strains were represented within ST5.
These results suggest that there may be specific S.aureus lineages which possess phenotypic and genotypic characteristics that enable them to more effectively cause sight-threatening keratitis. Future work will examine their virulence traits and a comparison to commensal S.aureus strains.
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