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International Journal of Microbiology
Volume 2012, Article ID 391251, 4 pages
Research Article

Comparison of Disk Diffusion and Etest Methods to Determine the Susceptibility of Staphylococcus aureus Circulating in Riyadh, Saudi Arabia to Fusidic Acid

1Department of Pathology, Microbiology Unit, College of Medicine, King Saud University and King Khalid University Hospital, Riyadh 11411, Saudi Arabia
2Department of Laboratory Medicine, Yale School of Medicine, New Haven, CT 06510, USA
3Pathology and Laboratory Medicine Service, Veteran Affairs (VA) Connecticut Healthcare System, West Haven, CT 06516, USA
4Departments of Pediatrics and Pharmacology, Yale School of Medicine, New Haven, CT 06510, USA
5Department of Medical Sciences, The Frank H. Netter MD School of Medicine, Quinnipiac University, Hamden, CT 06518-7908, USA

Received 12 March 2012; Revised 24 May 2012; Accepted 7 June 2012

Academic Editor: John Tagg

Copyright © 2012 Ali M. Somily et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Fusidic acid is a common therapy for staphylococcal infections in Saudi Arabia, but reports have suggested high rates of resistance among clinical isolates. Susceptibility testing of S. aureus to fusidic acid is further complicated by the lack of consensus on mean inhibitory concentrations (MIC) and disk diffusion cutoffs to determine resistance. The purpose of this study was to determine the correlation between disk diffusion and Etest determined MIC susceptibility results in clinical isolates of S. aureus from a large academic hospital in Riyadh, Saudi Arabia. Our data demonstrate excellent correlation between Etest determined MIC and disk diffusion susceptibility data, using either previously proposed zone sizes of ≥21 mm as susceptible and ≤18 mm as resistant or the EUCAST recommended zone size of ≤24 mm for resistance, in an area with relatively high rates of fusidic acid resistance.