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Development of EUCAST zone diameter breakpoints and quality control range for Staphylococcus aureus with ceftaroline
L M Koeth1, E Matuschek, G Kahlmeter
1Laboratory Specialists, Inc, 1651 A Crossings Parkway, Westlake, OH, 44145, USA, lkoeth@labspec.org.
Summary
This study established EUCAST breakpoints for ceftaroline susceptibility testing in Staphylococcus aureus. The 5-μg disk diffusion method showed high agreement with MIC testing for both MRSA and MSSA.
Area of Science:
- Microbiology
- Clinical Science
- Antimicrobial Resistance
Background:
- Accurate susceptibility testing is crucial for guiding antibiotic therapy against Staphylococcus aureus.
- Establishing standardized breakpoints ensures consistent interpretation of antimicrobial susceptibility test results.
- Ceftaroline is an important antibiotic for treating infections caused by Staphylococcus aureus, including methicillin-resistant strains.
Purpose of the Study:
- To establish EUCAST (European Committee on Antimicrobial Susceptibility Testing) zone diameter breakpoints for ceftaroline disk diffusion testing against Staphylococcus aureus.
- To evaluate the agreement between ceftaroline disk diffusion and broth microdilution methods.
- To determine quality control (QC) ranges for ceftaroline disk diffusion testing.
Main Methods:
- Ceftaroline susceptibility testing using 5-μg disk diffusion and broth microdilution methods.
- Testing of a challenge set including 70 methicillin-resistant Staphylococcus aureus (MRSA) and 30 methicillin-susceptible Staphylococcus aureus (MSSA) isolates.
- Molecular testing (mecA, MLST, PBP analysis) on selected isolates with borderline results.
- Quality control testing using Staphylococcus aureus ATCC 29213.
Main Results:
- High categorical agreement between disk diffusion and MIC methods: 100% for MSSA and 92% for MRSA.
- Established susceptible breakpoint for ceftaroline disk diffusion: Susceptible ≥20 mm, Resistant <20 mm.
- Established QC range for S. aureus ATCC 29213: 24-30 mm.
- No common molecular differences identified in strains with borderline ceftaroline MICs.
Conclusions:
- The 5-μg ceftaroline disk diffusion method is reliable for determining susceptibility in Staphylococcus aureus.
- The established EUCAST breakpoints provide a standardized approach for interpreting ceftaroline susceptibility.
- These findings support the clinical utility of ceftaroline for treating S. aureus infections.
