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Evaluation of different disk diffusion/media combinations for detection of methicillin resistance in Staphylococcus aureus and coagulase‐negative staphylococci
Author(s) -
SKOV ROBERT,
LARSEN ANDERS RHOD,
FRIMODTMØLLER NIELS,
ESPERSEN FRANK
Publication year - 2003
Publication title -
apmis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.909
H-Index - 88
eISSN - 1600-0463
pISSN - 0903-4641
DOI - 10.1034/j.1600-0463.2003.1110909.x
Subject(s) - coagulase , staphylococcus aureus , agar , microbiology and biotechnology , agar diffusion test , micrococcaceae , sccmec , methicillin resistant staphylococcus aureus , agar plate , staphylococcus , biology , bacteria , antibacterial agent , antibiotics , genetics
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.