title: Disk Diffusion Testing for Detection of Methicillin-Resistant Staphylococci: Does Moxalactam Improve upon Cefoxitin?
abstract: Disk diffusion testing is widely used to detect methicillin resistance in staphylococci, and cefoxitin is currently considered the best marker for mecA-mediated methicillin resistance. In low-inoculum diffusion testing (colony suspension at 106CFU/ml), the addition of moxalactam in combination with cefoxitin has been reported to improve on cefoxitin alone for the detection of methicillin-heteroresistant staphylococci. However, moxalactam is absent from EUCAST and CLSI guidelines, which use high-inoculum diffusion testing (colony suspension at 108CFU/ml), calling into question the potential interest of including moxalactam in their recommendations. The inhibition zone diameters of cefoxitin and moxalactam, alone and in combination, were evaluated for concordance with mecA and mecC positivity in a large collection of clinical Staphylococcus isolates (611 Staphylococcus aureus, Staphylococcus lugdunensis, and Staphylococcus saprophyticus isolates and 307 coagulase-negative staphylococci other than S. lugdunensis and S. saprophyticus isolates, of which 22% and 53% were mecA-positive, respectively) and in 25 mecC-positive S. aureus isolates using high-inoculum diffusion testing. Receiver operating characteristic, sensitivity, and specificity analyses indicated that the detection of mecA- and mecC-positive and negative isolates did not improve with moxalactam, either alone or in combination with cefoxitin, compared to cefoxitin alone. These findings were similar in both the S. aureus/S. lugdunensis/S. saprophyticus group and in the coagulase-negative staphylococci group. Our results do not support the use of moxalactam as an additional marker of methicillin resistance when testing with high-inoculum disk diffusion.
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.
authors.forename: Marie
authors.initials: M
authors.lastname: Bonjean
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.|CIRI, International Center for Infectiology Research, Lyon, France.|INSERM U1111, Université Lyon 1, Ecole Normale Supérieure de Lyon, CNRS UMR5308, Lyon, France.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Hodille
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.|CIRI, International Center for Infectiology Research, Lyon, France.|INSERM U1111, Université Lyon 1, Ecole Normale Supérieure de Lyon, CNRS UMR5308, Lyon, France.
authors.forename: Oana
authors.initials: O
authors.lastname: Dumitrescu
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.|CIRI, International Center for Infectiology Research, Lyon, France.|INSERM U1111, Université Lyon 1, Ecole Normale Supérieure de Lyon, CNRS UMR5308, Lyon, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Dupieux
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.
authors.forename: Christina
authors.initials: C
authors.lastname: Nkoud Mongo
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.
authors.forename: Camille
authors.initials: C
authors.lastname: Allam
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.
authors.forename: Mathilde
authors.initials: M
authors.lastname: Beghin
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.
authors.forename: Mickael
authors.initials: M
authors.lastname: Paris
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.
authors.forename: Ophelie
authors.initials: O
authors.lastname: Borrel
authors.affiliation: Centre Hospitalier du Pays d'Aix, Service de diagnostic biologique des maladies infectieuses, Aix en Provence, France.
authors.forename: Hubert
authors.initials: H
authors.lastname: Chardon
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.|CIRI, International Center for Infectiology Research, Lyon, France.|INSERM U1111, Université Lyon 1, Ecole Normale Supérieure de Lyon, CNRS UMR5308, Lyon, France.
authors.forename: Fréderic
authors.initials: F
authors.lastname: Laurent
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France.|CIRI, International Center for Infectiology Research, Lyon, France.|INSERM U1111, Université Lyon 1, Ecole Normale Supérieure de Lyon, CNRS UMR5308, Lyon, France.
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Rasigade
authors.affiliation: IAI, Hospices Civils de Lyon, Lyon, France gerard.lina@univ-lyon1.fr.|CIRI, International Center for Infectiology Research, Lyon, France.|INSERM U1111, Université Lyon 1, Ecole Normale Supérieure de Lyon, CNRS UMR5308, Lyon, France.
authors.forename: Gerard
authors.identifier: 0000-0002-9236-7998
authors.initials: G
authors.lastname: Lina
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D002440:Cefoxitin / Q000494:pharmacology*; D052978:Disk Diffusion Antimicrobial Tests / Q000379:methods*; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D009070:Moxalactam / Q000494:pharmacology*; D046915:Penicillin-Binding Proteins / Q000235:genetics; D057787:Staphylococcus lugdunensis / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification; D057790:Staphylococcus saprophyticus / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus; D002440:Cefoxitin; D009070:Moxalactam