Methods: A total of 6,865 GP pathogens from 60 medical centers from 36 states were submitted. The organism groups (no.overall) were: S. aureus (SA; 3,106), coagulase-negative staphylococci (CoNS; 797), enterococci (ENT; 855), S. pneumoniae (SPN; 874), viridans group (VGS; 359), and β-hemolytic streptococci (BHS; 874). All susceptibility (S) testing was performed by reference broth microdilution methods. LZD-R isolates were confirmed by Etest (bioMerieux, Hazelwood, MO) and by repeated reference S testing. PCR and sequencing was performed to detect mutations in 23S rRNA, L3, L4, and L22 proteins, and an acquired gene (cfr).
LZD activity against GP organisms remains high (99.78% S). The MIC50/90 for SA was at 1/1 μg/ml. MRSA rates were at 47.2% (47.9% in 2013; declining since 2007 [58.2%]). Among the LZD-non-S (NS) MRSA, one strain harbored cfr only (MIC, 4 µg/ml), one harbored G2576T (MIC, 8 µg/ml) and one contained cfr and G2576T with L3 changes (MIC, ≥8 µg/ml). Among CoNS, six isolates, 0.75% of all strains (0.52% in 2013, 0.92% in 2012) demonstrated LZD MIC results of ≥4 μg/ml. Five of these were identified as S. epidermidis; 4 of which contained cfr in addition to the presence of mutations in the ribosomal proteins L3 and L4, alone or in combination with 23S rRNA (G2576T) mutations. Six ENT (0.7%) were LZD-NS (≥4 μg/ml; G2576T mutations and one with an additional cfr). LZD was active against all SPN and BHS with a MIC50/90 of 1/1, μg/ml and VGS with an MIC50/90of 0.5/1 μg/ml. SPN penicillin NS (MIC, ≥0.12 μg/ml) occurred at a rate of 41.5% and NS ceftriaxone at 7.2%.
Conclusion: LZD demonstrates excellent activity and a sustained susceptibility rate of 99.78% overall (99.62-99.83% during 2008-2013 LEADER Program). LZD MIC population distributions remained unchanged without evidence of “MIC creep” among monitored, indicated species.
J. M. Streit,
J. E. Ross, Pfizer: Research Contractor , Research support
R. E. Mendes, Pfizer: Research Contractor , Research support
R. N. Jones, Pfizer: Research Contractor , Research support
P. A. Hogan, Pfizer: Employee , Salary