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2008 OMIG, Abstract 14

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Characterization of keratitis-associated Staphylococcus aureus infections from the Boston area
Irmgard Behlau1,2,3, Elizabeth M. Leonard1, Susan R. Heimer2,3, Jacqueline N. Martin1,2, Claes H. Dohlman1,2,3, Michael S. Gilmore1,2,3
1Massachusetts Eye and Ear Infirmary, 2The Schepens Eye Research Institute,
3Dept of Ophthalmology, Harvard Medical School, Boston, MA

Purpose: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 the organisms. This is an epidemiologic analysis of the risk factors and strain characteristics of keratitis-associated S. aureus clinical isolates.
Methods:Prospective collection of all clinical isolates of S. aureus from Oct 2006 through Sept 2008 submitted to the Clinical Microbiology laboratory at the MEEI.  The diagnosis of clinical keratitis and associated risk factors was by medical record review.  Antibiotic susceptibility data was performed by NCCLS standards. Biofilm formation was measured by Gentian violet staining. 
Results:Over the nearly 24 month period, the number of S. aureus keratitis proven cases cultured where only 28 cases out of nearly 600 S. aureus clinical isolates. Similar risk factors associated with S.aureus keratitis included trauma, ocular surface disease, and prior surgery as reported in the literature.  Soft contact lens wear and/or presence of a foreign body appears to also be a significant risk factor.  All of the methicillin-resistant strains (9/28) were also ciprofloxacin-resistant (10/28).  All 28 isolates were tetracycline- and trimethoprim-sulfamethoxazole- sensitive. Prior antibiotic usage did affect the resistance pattern. Biofilm formation was variable.
Conclusions:The decision to culture and risk factors identified include the presence of a foreign body, recent surgery, and failure of empiric therapy. The phenotypic diversity of S.aureus strains to cause keratitis may reflect the ability of a normal skin commensal in the presence of a corneal damage or a foreign body, including soft contact lenses, to cause disease.  Future work will examine species lineages and virulence traits.  The limitations of this study are its small sample size and possible culturing selection bias.  Future prospective multi-center studies of bacterial keratitis are encouraged.

Financial Disclosure: N; Funding: Fight for Sight (I.B.); The KPro Fund

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