D-2249. Comparative Evaluation of Ceftaroline MIC Testing with Etest and CLSI Broth Microdilution Methods
Session: Poster Session: Antimicrobial Susceptibility Testing 2008
Monday, October 27, 2008: 12:00 AM
Room: Hall C
Background: Ceftaroline (CPT) is a novel, parenteral, broad-spectrum cephalosporin with bactericidal activity against Gram-positive organisms, including methicillin-resistant (MR) S. aureus (MRSA), multidrug-resistant S. pneumoniae, as well as common Gram-negative pathogens. CPT is currently in phase 3 development. The performance of a new Etest CPT strip was compared to the CLSI broth microdilution (BMD) method using a set of challenge strains. Methods: Etest CPT (MIC 0.002 - 32 µg/mL) and BMD were performed with recommended procedures. Test strains (39) used are listed in the result table. The following ATCC® strains were tested: E. coli 25922, P. aeruginosa 27853, E. faecalis 29212, S. aureus 29213 (methicillin susceptible S. aureus, MSSA), 43300 (MRSA), 700699 (vancomycin intermediate S. aureus, VISA) and 700698 (hVISA). The effects of inoculum variation (100 fold) were studied with QC strains. Results:
Species (N)MIC range µg/mL
E. coli (6)0.047-1
Enterobacter spp. (7)0.047- >32
K. pneumoniae (6)0.094-12
P. mirabilis (2)0.047-0.094
Serratia & Citrobacter spp.(2)0.75-1
E. faecalis (2)0.5-2
MSSA (5)0.094-0.25
MRSA+VISA/hVISA (6)0.38-1.5
MR-coag. neg. staphylococci (3)0.094-0.38

Excellent agreement was seen between Etest and BMD (100% ±1 dilution) for the challenge organisms that had a wide range of MIC values. QC results for both methods fell within the CLSI specifications. Inoculum effects on MIC values were minimal. Conclusions: Substantially equivalent MIC results for CPT can be obtained by Etest and the CLSI reference method. The wide concentration range in Etest (15 dilutions) and simplicity of use makes it a useful and convenient tool for MIC testing during drug development and for subsequent clinical use.
Anette Engelhardt1, Anne Yusof2, Carolina Johansson2, Karin Sjöström1, Phion Ho2 and  A. Engelhardt,
AB BIODISK Role(s): Employee., (1)AB BIODISK, Solna, Sweden, (2)AB BIODISK