title: Development of EUCAST zone diameter breakpoints and quality control range for Staphylococcus aureus with ceftaroline 5-μg disk.
abstract: This ceftaroline MIC/disk comparison study for Staphylococcus aureus was performed for the purpose of establishing EUCAST zone diameter breakpoints. Ceftaroline susceptibility for a challenge set of 70 methicillin resistant- and 30 methicillin susceptible-S. aureus was determined by 5-μg disk diffusion and broth microdilution methods. Seventeen isolates were retested by disk and MIC, and the remaining 83 isolates were retested by MIC. Molecular testing was performed on 19 isolates with borderline susceptible ceftaroline MIC results to assess any differences in mecA and epidemiological correlation. An additional set of 101 consecutive clinical S. aureus isolates were tested using the 5-μg disk. S. aureus ATCC 29213 was tested by multiple sites and media for QC range determination. Replicate MIC results were within ±1 doubling dilution, with tendency for slightly lower repeat MICs, and there was minimal variation in replicate zone results. Based on susceptible breakpoints for MIC of ≤1 mcg/mL and for disk of >20 mm, there was 100 % categorical agreement for 30 MSSA and 92 % categorical agreement for 70 MRSA. There were no common MLST or PBP changes for strains with MICs of 1 and 2 mcg/mL. All ceftaroline disk results for the consecutively collected isolates were >20 mm. EUCAST selected the ceftaroline 5-μg disk breakpoint of Susceptible ≥20, Resistant <20 mm because it correlated best with the MIC breakpoint of Susceptible ≤1, Resistant >1 mg/L. A ceftaroline 5-μg disk QC range for S. aureus ATCC 29213 of 24-30 mm was also established by EUCAST.
authors.affiliation: Laboratory Specialists, Inc, 1651 A Crossings Parkway, Westlake, OH, 44145, USA, lkoeth@labspec.org.
authors.forename: L M
authors.initials: LM
authors.lastname: Koeth
authors.forename: E
authors.initials: E
authors.lastname: Matuschek
authors.forename: G
authors.initials: G
authors.lastname: Kahlmeter
authors.forename: R A
authors.initials: RA
authors.lastname: Alm
authors.forename: J E
authors.initials: JE
authors.lastname: Ambler
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002511:Cephalosporins / Q000494:pharmacology*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000592:standards; D011786:Quality Control; D013211:Staphylococcus aureus / Q000187:drug effects*; D000097583:Ceftaroline
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D000097583:Ceftaroline
references.citation: J Antimicrob Chemother. 2012 Jun;67(6):1321-4
references.pmid: 22398650
references.citation: Diagn Microbiol Infect Dis. 2013 Jan;75(1):86-8
references.pmid: 23146404