Interpretation of Diffusion Susceptibility Data Obtained with 10-μg Fucidin (Sodium Fusidate) Disks against Clinical Isolates of Staphylococcus aureus

Abstract

A total of 109 clinical isolates of Staphylococcus aureus as well as 2 isolates of S.epidermidis, 11 isolates of group A β-hemolytic streptococci, 32 isolates of enterococci and 1 strain of α-hemolytic streptococcus were tested for susceptibility to fucidin (the sodium salt of fusidic acid) by the standardized Bauer-Kirby disk diffusion technique and a microtiter broth dilution method. The data obtained led to the following proposed criteria for the interpretation of inhibition zones around 10-μg fucidin disks: staphylococcal isolates that yield zones of inhibition equal to or greater than 20 mm in diameter are designated as sensitive to the drug: those isolates that are characterized by zones of 19 mm or less in diameter are interpreted as resistant to the drug. Intermediate (equivocal) zone criteria are not proposed.