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Updated: Jun 25, 2026

Biosensor for Detection of Antibiotic Resistant Staphylococcus Bacteria
Published on: May 8, 2013
Effects of temperature on the detection of methicillin resistance in Staphylococcus aureus using cefoxitin disc
1National Center for Antimicrobials and Infection Control, Statens Serum Institut, Copenhagen, Denmark. rsk@ssi.dk
Objectives:
Cefoxitin is today the substance of choice for the phenotypic detection of methicillin-resistant Staphylococcus aureus (MRSA). We investigated the influence of incubation temperature in the standard range, i.e. 35-37 degrees C, and time, i.e. 18-20 h, versus a full 24 h.
Methods:
Cefoxitin disc testing was examined at incubation temperatures of 35 and 36 degrees C and times of 18-20 and 24 h, respectively, for 94 mecA-negative and 49 mecA-positive S. aureus on Iso-Sensitest agar using a semi-confluent inoculum.
Results:
Cefoxitin inhibition zones on Iso-Sensitest agar were larger at temperatures above 35 degrees C; two isolates (4%, 95% confidence interval=0.5-14%) incubated at 36 degrees C were falsely categorized as susceptible to methicillin. Incubation time across 18-24 h did not impact results.
Conclusions:
Detection of methicillin resistance in S. aureus using the cefoxitin disc method with a semi-confluent inoculum on Iso-Sensitest agar is influenced by incubation temperature, and the temperature should not exceed 35 degrees C for the reliable detection of MRSA.
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