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Staphylococcus aureus ocular isolates from symptomatic adverse events: antibiotic resistance and similarity of bacteria causing adverse events.

Schubert TL, Hume EB, Willcox MD

The School of Optometry and Vision Science, University of New South Wales, NSW, Australia. t.schubert@ier.org.au

BACKGROUND: Staphylococcus is the leading cause of microbial keratitis. Staphylococcus aureus isolated from ocular infections with resistance to a wide range of antibiotics, including the commonly prescribed fluoroquinolones, is emerging. The aim of this study was to determine the current antibiotic susceptibilities of ocular S. aureus isolates and also determine whether isolates from different adverse events or those with similar antimicrobial susceptibilities are related. METHODS: A collection of 55 S. aureus strains from ocular adverse events were analysed for antibiotic susceptibility using disc diffusion (CDS method) and typed using PCR-ribotyping and pulsed-field gel electrophoresis (PFGE). RESULTS: S. aureus isolated from symptomatic ocular adverse events in the USA exhibited greater resistance to antibiotics than did those isolated from symptomatic ocular adverse events in Australia or India (p<0.05). A larger proportion of ulcerative keratitis isolates was found to be resistant to antibiotics than isolates from conjunctivitis. PFGE analysis separated related isolates determined by ribotype, on the basis of the adverse event caused by the isolate. Isolates were related within geographical regions and adverse event types. CONCLUSIONS: Similar isolates within a geographical location cause adverse events but there is a genetic difference between isolates causing corneal adverse events and those causing conjunctivitis. Isolates from corneal adverse events were more resistant to antibiotics, with those from the USA exhibiting the greatest resistance. This suggests that virulence may correlate with increased resistance to antibiotics.

Published 14 February 2008 in Clin Exp Optom, 91(2): 148-55.
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