1703. Efficacy of Selected Metabolic Inhibitors for the Prevention and Resensitization of High-Level Daptomycin Resistance in Streptococcus mitis-oralis In Vitro and in an Ex Vivo Simulated Endocarditis Model

BACKGROUND: Rapid development of stable, high-level daptomycin-resistance (DAP-R) is frequent among Streptococcus mitis-oralis strains during exposure to DAP in vitro and in vivo. Metabolomic analyses of in vitro-derived daptomycin-resistant (DAP-R) S. mitis-oralis strains (351D10) revealed substantial glycolytic pathway differences vs. its DAP-susceptible (DAP-S) parental strain, 351. To define translatability of such metabolic changes, we assessed combinations of DAP + strategic metabolic inhibitors likely to impact such pathways, including: oxamic acid [OXA], trimetazidine [TMZ) and 6-mercaptopurine [6-MP]. We assessed these combinations vs. our DAP-S/DAP-R isogenic strain pair both in vitro and ex vivo for: bactericidal and synergistic activities; prevention of high-level DAP-R in DAP-S cells; and/or resensitization of DAP-R cells METHODS: MICs. E test and microbroth dilution In vitro antimicrobial combination assays. Time-kill curves (24 hr) and serial passaging in DAP (10 d). Ex vivo IE model: SEVs (simulated endocardial vegetation’s) were quantitatively cultured at serial time-points post-exposures to DAP +/- inhibitors (0, 4, 8, 24, 32, 48 hr). RESULTS: In vitro , combinations of DAP + OXA or DAP + TMZ, as well as OXA or TMZ monotherapy, exerted bactericidal effect against both strains. Moreover, DAP + 6-MP yielded both a bactericidal, as well as synergistic activity against DAP-S 351 (but not against DAP-R 351 D10). None of the combinations prevented the development of DAP-R or resensitized the DAP-R strain to a DAP-S phenotype in vitro. In the ex vivo SEV model, using PK/PD simulations of humanized drug doses, DAP + OXA was the most effective regimen for both the DAP-S 351 and DAP-R 351 D10 strains; both OXA alone and DAP + OXA prevented DAP-R evolution, although not resensitizing the DAP-R strain to a DAP-S phenotype. CONCLUSION: Combinations of DAP plus specific metabolic inhibitors represents a promising approach to enhance killing of S. mitis-oralis strains, as well as to potentially forestall DAP-R emergence. Also, they do provide a solid platform upon which to explore other potential metabolic modifiers for their ability to enhance the efficacy of DAP, based on definable metabolic perturbations in DAP-R S. mitis-oralis. DISCLOSURES: All Authors: No reported disclosures.