1739. Trends of Ceftaroline (CPT) Activity Among Consecutive Methicillin-Resistant Staphylococcus aureus (MRSA) Blood Isolates and Correlation with Vancomycin (VAN) Activity
Session: Poster Abstract Session: Treatment of Bacteremia and Endocarditis
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C
Background: MRSA bacteremia is increasing and the level of MRSA susceptibility to VAN is gradually decreasing.  CPT is a broad-spectrum cephalosporin with MRSA coverage, approved for Community-acquired Bacterial Pneumonia and Acute Bacterial Skin and Soft Skin Structure Infections. We examined the activity of CPT against MRSA blood isolates.

Methods: We searched our laboratory log to identify MRSA blood isolates from 2002 to 2012. The first isolate per bacteremia episode was included.  S. aureus was identified on the basis of its morphology and the production of catalase and coagulase. MRSA blood-stream isolates were kept frozen at -80°C until the time of in vitro testing.  Susceptibility to VAN and CPT was tested in duplicate using broth microdilution according to recommended CLSI methodology.  Bactericidal activity was determined using time-kill curves in a randomly selected sample (at 4X MIC).

Results: Of 395 MRSA isolates, 41% were isolated from ICU patients. Culture sources included peripheral blood (71%), central vascular catheter (25%) and arterial line (4%). CPT MIC distribution was narrow with 95% of isolates exhibiting an MIC of 0.5-1 µg/mL. Of all isolates, 98% were susceptible to CPT (MIC ≤1 µg/mL). CPT MIC range, geometric mean MIC (GM-MIC), MIC50, and MIC90 were 0.25-2, 0.7, 0.5 and 1 µg/mL, respectively. CPT GM-MIC decreased during the study period, from 0.81 in 2002-3 to 0.61 µg/mL in 2011-2. Higher VAN MICs were associated with higher CPT MICs. CPT GM-MICs for isolates with a VAN MIC =<1 µg/mL and >1 µg/mL were 0.67 and 0.79 µg/mL, respectively. Still, 94% of isolates with VAN MIC >1 µg/mL were susceptible to CPT.  CPT GM-MIC were slightly higher among isolates from ICU patients as compared to ward patients (0.77 vs 0.71 µg/mL, respectively) and similar among isolates from peripheral blood and central lines. CPT was rapidly bactericidal for all tested isolates: >3 log inoculum reductions at 6 and 24 hrs were observed in 89% and 100% of tested isolates.

Conclusion: CPT susceptibility among MRSA blood isolates is within a tight MIC range and has not increased from 2002 to 2012. CPT activity is minimally affected by VAN MIC and it remains highly active against isolates with VAN MIC of >1 µg/mL.

Yoav Golan, MD MS, Division of Geographic Medicine and Infectious Diseases, Tufts Medical Center, Boston, MA, Laura Mcdermott, BS, Tufts Medical Center, Boston, MA and David Snydman, MD, FIDSA, Geographic Medicine and Infectious Diseases, Tufts Medical Center, Boston, MA

Disclosures:

Y. Golan, Cerexa: Consultant, Investigator, Scientific Advisor and Speaker's Bureau, Consulting fee, Research grant and Speaker honorarium

L. Mcdermott, Cerexa: Investigator, Research grant

D. Snydman, Merck, Cubist: Consultant, Grant Investigator, Scientific Advisor and Speaker's Bureau, Consulting fee, Research grant and Speaker honorarium

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