title: Evaluation of Oxacillin and Cefoxitin Disk and MIC Breakpoints for Prediction of Methicillin Resistance in Human and Veterinary Isolates of Staphylococcus intermedius Group.
abstract: Staphylococcus pseudintermedius is a coagulase-positive species that colonizes the nares and anal mucosa of healthy dogs and cats. Human infections with S. pseudintermedius range in severity from bite wounds and rhinosinusitis to endocarditis; historically, these infections were thought to be uncommon, but new laboratory methods suggest that their true incidence is underreported. Oxacillin and cefoxitin disk and MIC tests were evaluated for the detection of mecA- or mecC-mediated methicillin resistance in 115 human and animal isolates of the Staphylococcus intermedius group (SIG), including 111 Staphylococcus pseudintermediusand 4 Staphylococcus delphini isolates, 37 of which were mecA positive. The disk and MIC breakpoints evaluated included the Clinical and Laboratory Standards Institute (CLSI) M100-S25 Staphylococcus aureus/Staphylococcus lugdunensis oxacillin MIC breakpoints and cefoxitin disk and MIC breakpoints, the CLSI M100-S25 coagulase-negative Staphylococcus (CoNS) oxacillin MIC breakpoint and cefoxitin disk breakpoint, the CLSI VET01-S2 S. pseudintermedius oxacillin MIC and disk breakpoints, and the European Committee on Antimicrobial Susceptibility Testing (EUCAST) S. pseudintermedius cefoxitin disk breakpoint. The oxacillin results interpreted by the VET01-S2 (disk and MIC) and M100-S25 CoNS (MIC) breakpoints agreed with the results of mecA/mecC PCR for all isolates, with the exception of one false-resistant result (1.3% of mecA/mecC PCR-negative isolates). In contrast, cefoxitin tests performed poorly, ranging from 3 to 89% false susceptibility (very major errors) and 0 to 48% false resistance (major errors). BD Phoenix, bioMérieux Vitek 2, and Beckman Coulter MicroScan commercial automated susceptibility test panel oxacillin MIC results were also evaluated and demonstrated >95% categorical agreement with mecA/mecC PCR results if interpreted by using the M100-S25 CoNS breakpoint. The Alere penicillin-binding protein 2a test accurately detected all mecA-positive isolates, although for four isolates, cefoxitin induction was required prior to testing. These data demonstrate that the cefoxitin surrogate test does not reliably detect the presence of mecA in S. pseudintermedius isolates and that laboratories should perform oxacillin disk or MIC tests of these isolates when they are encountered.
authors.affiliation: UCLA David Geffen School of Medicine, Los Angeles, California, USA Landstuhl Regional Medical Center, Landstuhl, Germany.
authors.forename: M T
authors.initials: MT
authors.lastname: Wu
authors.affiliation: Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: C-A D
authors.identifier: http://orcid.org/0000-0002-1137-840X
authors.initials: CA
authors.lastname: Burnham
authors.affiliation: Weill Cornell Medical College, New York, New York, USA.
authors.forename: L F
authors.initials: LF
authors.lastname: Westblade
authors.affiliation: Children's Hospital of Los Angeles, Los Angeles, California, USA.
authors.forename: J
authors.initials: J
authors.lastname: Dien Bard
authors.affiliation: Veterinary Medicine and Biomedical Sciences, Texas A&M University, College Station, Texas, USA.
authors.forename: S D
authors.identifier: http://orcid.org/0000-0001-9154-8909
authors.initials: SD
authors.lastname: Lawhon
authors.affiliation: Washington University School of Medicine, St. Louis, Missouri, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Wallace
authors.affiliation: Emory University School of Medicine, Atlanta, Georgia, USA.
authors.forename: T
authors.initials: T
authors.lastname: Stanley
authors.affiliation: Emory University School of Medicine, Atlanta, Georgia, USA Emory Antibiotic Resistance Center, Atlanta, Georgia, USA.
authors.forename: E
authors.initials: E
authors.lastname: Burd
authors.affiliation: UCLA David Geffen School of Medicine, Los Angeles, California, USA.
authors.forename: J
authors.initials: J
authors.lastname: Hindler
authors.affiliation: UCLA David Geffen School of Medicine, Los Angeles, California, USA rhumphries@mednet.ucla.edu.
authors.forename: R M
authors.initials: RM
authors.lastname: Humphries
mesh_terms: D000818:Animals; D002440:Cefoxitin / Q000494:pharmacology*; D006801:Humans; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests / Q000379:methods / Q000592:standards*; D010068:Oxacillin / Q000494:pharmacology*; D013203:Staphylococcal Infections / Q000382:microbiology* / Q000662:veterinary*; D057789:Staphylococcus intermedius / Q000187:drug effects*
chemical_list: D002440:Cefoxitin; D010068:Oxacillin