475Telavancin (TLV) In vitro Activity Tested Against a USA Collection of Methicillin-resistant Staphylococcus aureus (MRSA), Including a Multidrug-resistant (MDR) Subset (2011-2013)

Background. The broth microdilution (BMD) method for telavancin (TLV) was recently revised by the FDA and CLSI. This study assessed the TLV activity using a revised BMD (rBMD) method, following the CLSI guidelines for water-insoluble agents. Polysorbate-80 was added in the test medium. This rBMDmethod was deemed necessary for greater accuracy and reproducibility of TLV MIC results. Methods. 9,610 S. aureuscollected from 28 USA sites were included. Susceptibility testing was performed based on CLSI guidelines (M07-A9 and M100-S24). MIC interpretation was guided by FDA (TLV) and CLSI (2014) criteria. MRSA resistant to ≥3 drug classes were defined as MDR. Results. TLV had MIC50, MIC90 and MIC100 of 0.03, 0.06 and 0.12 μg/mL, respectively, against methicillin-susceptible, MRSA, non-MDR and MDR subsets. MRSA with vancomycin (VAN) MIC = 2 μg/mL had TLV MIC50 (0.06 μg/mL) 2fold higher than those MRSAwith VANMIC at ≤1 μg/mL. These TLV MIC50 results were equivalent to those noted for MRSA categorized by the daptomycin (DAP) MICs. However, TLV had MIC90 and MIC100 results of 0.06 and 0.12 μg/mL, respectively, regardless of MRSA subset. VAN (MIC50/90, 1/1 μg/mL), DAP (MIC50/90, 0.25/0.5 μg/mL) and linezolid (MIC50/90, 1/1 μg/mL) were active against MDR (≥99.7% susceptible); however, TLV had MICs 8to 32-fold lower than these comparators.