title: Comparison of cefoxitin and moxalactam 30 microg disc diffusion methods for detection of methicillin resistance in coagulase-negative staphylococci.
abstract: OBJECTIVE
  To compare cefoxitin and/or moxalactam 30 microg disc diffusion (DD) methods to detect methicillin resistance in coagulase-negative staphylococci (CoNS) using both high- and low-density (HD/LD) inoculum techniques.
  
  
  METHODS
  A challenge set of 192 CoNS was tested. DD test results were compared with PBP2a detection.
  
  
  RESULTS
  With the LD inoculum, the sensitivity/specificity of cefoxitin and moxalactam were 94.4%/100% and 100%/92.4%, respectively, using the DD breakpoints of the Comité de l'Antibiogramme de la Société Française de Microbiologie. With the HD inoculum, the sensitivity/specificity of cefoxitin and moxalactam were 93.7%/100% and 100%/96.9%, using the cefoxitin DD breakpoints of the CLSI and a resistant/susceptible breakpoint of < 20 mm/>or=20 mm for moxalactam. Comparison of receiver operating characteristic AUCs did not show significant difference between studied assays, but the overlapping zone where both PBP2a-positive and PBP2a-negative isolates were observed concerned a lower number of strains with moxalactam than with cefoxitin (P < 0.001). Combination of cefoxitin and moxalactam DD methods demonstrated that all isolates with a concordant cefoxitin/moxalactam phenotype were correctly classified. Interestingly, all isolates misclassified by each DD method used alone were cefoxitin-susceptible and moxalactam-resistant.
  
  
  CONCLUSIONS
  Although all DD methods studied here performed well for detecting methicillin resistance in CoNS, moxalactam had a higher accuracy than cefoxitin to differentiate heteroresistant isolates from PBP2a-negative strains. Identification of isolates that should be submitted to a confirmatory test to conclude on methicillin resistance can be easily obtained by combining cefoxitin and moxalactam DD methods.
authors.affiliation: Microbiology Laboratory, Necker-Enfants Malades Hospital, Faculté de Médecine Paris-Descartes, 149 rue de Sèvres, 75015, Paris, France. join@necker.fr
authors.forename: Olivier F
authors.initials: OF
authors.lastname: Join-Lambert
authors.forename: Sylvain
authors.initials: S
authors.lastname: Clauser
authors.forename: Christelle
authors.initials: C
authors.lastname: Guillet
authors.forename: Jean-Philippe
authors.initials: JP
authors.lastname: Jais
authors.forename: Eric
authors.initials: E
authors.lastname: Abachin
authors.forename: Gilles
authors.initials: G
authors.lastname: Quesnes
authors.forename: Etienne
authors.initials: E
authors.lastname: Carbonnelle
authors.forename: Alban
authors.initials: A
authors.lastname: Le Monnier
authors.forename: Jean-Ralph
authors.initials: JR
authors.lastname: Zahar
authors.forename: Samer
authors.initials: S
authors.lastname: Kayal
authors.forename: Patrick
authors.initials: P
authors.lastname: Berche
authors.forename: Agnès
authors.initials: A
authors.lastname: Ferroni
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000378:metabolism; D002440:Cefoxitin / Q000494:pharmacology*; D003030:Coagulase / Q000378:metabolism; D016106:Methicillin Resistance / Q000187:drug effects*; D008826:Microbial Sensitivity Tests; D009070:Moxalactam / Q000494:pharmacology*; D046915:Penicillin-Binding Proteins / Q000378:metabolism; D012372:ROC Curve; D013210:Staphylococcus / Q000187:drug effects* / Q000201:enzymology; D013212:Staphylococcus epidermidis / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D003030:Coagulase; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus; D002440:Cefoxitin; D009070:Moxalactam