Evaluation of different disk diffusion/media combinations for detection of methicillin resistance in Staphylococcus aureus and coagulase-negative staphylococci
Abstract:Skov R, Larsen AR, Frimodt-Møller N, Espersen F. Evaluation of different disk diffusion/media combinations for detection of methicillin resistance in Staphylococcus aureus and coagulase-negative staphylococci. APMIS 2003;111:905–14.
In order to find a disk diffusion method with both high sensitivity and specificity for determination of methicillin resistance primarily for S. aureus but also for coagulase-negative staphylococci we screened several methodological variants using a material of 66 S. aureus comprising of 11 methicillin-susceptible, 18 borderline-resistant, and 37 methicillin-resistant strains. Only four of the combinations studied performed with both high sensitivity and specificity. Two of these, the Columbia agar +4.5% NaCl and Mueller Hinton agar +2% NaCl combined with a 5 μg oxacillin disk, confluent inoculum and 24 h incubation at 35 °C were further evaluated using 105 MRSA and 91 mecA-negative S. aureus and 193 clinical isolates of coagulase-negative staphylococci. The Columbia agar +4.5% NaCl performed excellently for both S. aureus and coagulase-negative staphylococci. For Columbia agar +4.5% NaCl using a 5 μg oxacillin disk we suggest an interpretive zone diameter of R≤15 mm and S≥16 mm for S. aureus and R≤24 mm and S≥26 mm for coagulase-negative staphylococci. The Mueller Hinton agar +2% NaCl performed well for coagulase-negative staphylococci but for S. aureus at least three (3%) very major errors were found, making this method less attractive.
Document Type: Research Article
Affiliations: Sector for Microbiology, Statens Serum Institut, Copenhagen, Denmark
Publication date: September 1, 2003