title: Evaluation of a cefoxitin 30 microg disc on Iso-Sensitest agar for detection of methicillin-resistant Staphylococcus aureus.
abstract: OBJECTIVE
  To evaluate the performance of a cefoxitin 30 microg disc on Iso-Sensitest agar, using a semi-confluent inoculum and overnight incubation at 35-36 degrees C, for detection of methicillin-resistant Staphylococcus aureus (MRSA).
  
  
  METHODS
  A total of 457 S. aureus, including 190 MRSA of several defined PFGE types and a number of low-level resistant isolates, were tested with a cefoxitin 30 microg disc on Iso-Sensitest agar, using a semi-confluent inoculum and overnight incubation at 35-36 degrees C. This method was compared with the standard SRGA (Swedish Reference Group for Antibiotics) method (oxacillin 1 microg disc on Iso-Sensitest agar supplemented with 5% defibrinated horse blood, confluent growth and 24 h incubation in ambient air at 30 degrees C).
  
  
  RESULTS
  The cefoxitin method was excellent, with a sensitivity of 100% and a specificity of 99% using an interpretative zone diameter of S > or = 29 mm and R < 29 mm. Its performance was much better than the SRGA method, which with this collection of difficult strains had a sensitivity of only 78% using the current breakpoint of S > or = 12 mm.
  
  
  CONCLUSIONS
  We suggest that the cefoxitin method should replace that currently recommended by the SRGA for the detection of MRSA, and that it would fit well into BSAC methodology.
authors.affiliation: National Center for Antimicrobials and Infection Control, Statens Serum Institut, Artillerivej 5, DK-2300 Copenhagen S, Denmark. rsk@ssi.dk
authors.forename: R
authors.initials: R
authors.lastname: Skov
authors.forename: R
authors.initials: R
authors.lastname: Smyth
authors.forename: M
authors.initials: M
authors.lastname: Clausen
authors.forename: A R
authors.initials: AR
authors.lastname: Larsen
authors.forename: N
authors.initials: N
authors.lastname: Frimodt-Møller
authors.forename: B
authors.initials: B
authors.lastname: Olsson-Liljequist
authors.forename: G
authors.initials: G
authors.lastname: Kahlmeter
mesh_terms: D000362:Agar / Q000494:pharmacology; D002440:Cefoxitin / Q000494:pharmacology*; D004353:Drug Evaluation, Preclinical / Q000379:methods; D006801:Humans; D016106:Methicillin Resistance / Q000502:physiology*; D008826:Microbial Sensitivity Tests / Q000379:methods / Q000706:statistics & numerical data; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification
chemical_list: D002440:Cefoxitin; D000362:Agar