1629. Vancomycin Resistance in Enterococcus faecium Clinical Isolates Responsible for Bloodstream Infections in US Hospitals Over Ten Years (2010-2019) and Activity of Oritavancin

BACKGROUND: Enterococcus faecium (EFM) causes difficult-to-treat infections due to its intrinsic resistance (R) and ability to acquire R to many antimicrobials. This study evaluated the vancomycin (VAN)-R rates over time and the activity of oritavancin (ORI) against a collection of EFM causing bloodstream infections (BSI). METHODS: A total of 1,081 BSI EFM isolates collected from 36 US hospitals in a prevalence mode design during 2010-2019 were evaluated. Bacterial identification was confirmed by MALDI-TOF MS. Susceptibility testing was performed by reference broth microdilution. For comparison, the ORI breakpoint for VAN-susceptible E. faecalis was applied to EFM. Isolates were characterized as VanA or VanB phenotypes based on their susceptibility (S) to VAN and teicoplanin (TEC). The VanB phenotype was confirmed by PCR and/or whole genome sequencing. RESULTS: Overall, 72.3% (782/1,081) of EFM were VAN-R (Table). VanA was the most common phenotype (97.7%; 764/782). The yearly VAN-R rates decreased from 81.8% in 2010 to 58.7% in 2019. A total of 18 (2.3%) isolates exhibited a VanB phenotype (TEC MIC, 0.5-8 mg/L); however, the vanB gene only was confirmed in 9 EFM isolates (TEC MIC, 0.5-1 mg/L), which were all collected in 2010-2012. The remaining 9 (50.0%) VanB phenotype EFM isolates carried a vanA gene (TEC MIC, 4-8 mg/L). ORI was very active against VAN-susceptible EFM (MIC(50/90), ≤ 0.008/≤0.008/mg/L), VanA (MIC(50/90), 0.03/0.12 mg/L; MIC(100,) 0.5 mg/L), and VanB (MIC(50/90), ≤ 0.008/0.015 mg/L; MIC(100,) 0.03 mg/L) subsets. Only linezolid (LZD) and ORI (MIC, ≤ 0.12 mg/L) showed > 95.0%S against EFM and VAN-R subsets. Daptomycin (DAP)-R rarely was observed (0.8%), but it was more frequently found in the last 5 years. However, 49.9% of EFM isolates showed elevated DAP MICs (2 and 4 mg/L). ORI inhibited 77.8%, and 100.0% of DAP-R and LZD-nonsusceptible EFM isolates at ≤ 0.12 mg/L, respectively. CONCLUSION: VAN-R rates among EFM causing BSI in the US decreased during 2010-2019. VanA remains the most common phenotype, whereas vanB-carrying isolates became rarer in later years. Interestingly, half of VanB-phenotype isolates carried a vanA gene. ORI was very active against EFM causing BSI, including isolates R to VAN, DAP, and/or nonsusceptible to LZD. Table 1 [Image: see text] DISCLOSURES: Cecilia G. Carvalhaes, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Pfizer (Research Grant or Support) Helio S. Sader, MD, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Melinta (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support) Jennifer M. Streit, BS, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support) Mariana Castanheira, PhD, 1928 Diagnostics (Research Grant or Support)A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Amplyx Pharmaceuticals (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cidara Therapeutics (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Fox Chase Chemical Diversity Center (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Merck & Co, Inc. (Research Grant or Support)Paratek Pharma, LLC (Research Grant or Support)Pfizer (Research Grant or Support)Qpex Biopharma (Research Grant or Support) Rodrigo E. Mendes, PhD, A. Menarini Industrie Farmaceutiche Riunite S.R.L. (Research Grant or Support)Allergan (Research Grant or Support)Allergan (Research Grant or Support)Basilea Pharmaceutica International, Ltd (Research Grant or Support)Cipla Ltd. (Research Grant or Support)Department of Health and Human Services (Research Grant or Support)GlaxoSmithKline (Research Grant or Support)Melinta Therapeutics, Inc. (Research Grant or Support)Merck (Research Grant or Support)Merck (Research Grant or Support)Pfizer (Research Grant or Support)