Activity of Ceftaroline and Epidemiologic Trends in Staphylococcus aureus Isolates Collected from 43 Medical Centers in the United States in 2009

Abstract

ABSTRACTAStaphylococcus aureussurveillance program was initiated in the United States to examine thein vitroactivity of ceftaroline and epidemiologic trends. Susceptibility testing by Clinical and Laboratory Standards Institute broth microdilution was performed on 4,210 clinically significant isolates collected in 2009 from 43 medical centers. All isolates were screened formecAby PCR and evaluated by pulsed-field gel electrophoresis. Methicillin-resistantS. aureus(MRSA) were analyzed for Panton-Valentine leukocidin (PVL) genes and the staphylococcal cassette chromosomemec(SCCmec) type. All isolates had ceftaroline MICs of ≤2 μg/ml with an MIC50of 0.5 and an MIC90of 1 μg/ml. The overall resistance rates, expressed as the percentages of isolates that were intermediate and resistant (or nonsusceptible), were as follows: ceftaroline, 1.0%; clindamycin, 30.2% (17.4% MIC ≥ 4 μg/ml; 12.8% inducible); daptomycin, 0.2%; erythromycin, 65.5%; levofloxacin, 39.9%; linezolid, 0.02%; oxacillin, 53.4%; tetracycline, 4.4%; tigecycline, 0%; trimethoprim-sulfamethoxazole, 1.6%; vancomycin, 0%; and high-level mupirocin, 2.2%. ThemecAPCR was positive for 53.4% of the isolates. The ceftaroline MIC90s were 0.25 μg/ml for methicillin-susceptibleS. aureusand 1 μg/ml for MRSA. Among the 2,247 MRSA isolates, 51% were USA300 (96.9% PVL positive, 99.7% SCCmectype IV) and 17% were USA100 (93.4% SCCmectype II). The resistance rates for the 1,137 USA300 MRSA isolates were as follows: erythromycin, 90.9%; levofloxacin, 49.1%; clindamycin, 7.6% (6.2% MIC ≥ 4 μg/ml; 1.4% inducible); tetracycline, 3.3%; trimethoprim-sulfamethoxazole, 0.8%; high-level mupirocin, 2.7%; daptomycin, 0.4%; and ceftaroline and linezolid, 0%. USA300 is the dominant clone causing MRSA infections in the United States. Ceftaroline demonstrated potentin vitroactivity against recentS. aureusclinical isolates, including MRSA, daptomycin-nonsusceptible, and linezolid-resistant strains.