Project Summary/Abstract The proposed project is an investigation of the synergistic activity of antimicrobial combinations against carbapenem-resistant Enterobacteriaceae (CRE). The principal investigator, Dr. Thea Brennan-Krohn, recently completed fellowships in Pediatric Infectious Diseases and in Medical Microbiology and is now an Instructor at Harvard Medical School and a post-doctoral fellow at Beth Israel Deaconess Medical Center. She is interested in improving methods for detection and characterization of antimicrobial synergy in order to guide the treatment of patients infected with highly resistant pathogens. Her career goal is to become a leading investigator in the development, implementation and interpretation of tests for detection of antimicrobial synergy. During the award period, she will obtain a Master of Science in Pharmacology and will pursue coursework in clinical and translational research. The proposed research will be carried out under the mentorship of James Kirby, MD, D(ABMM), an NIH-funded investigator at Beth Israel Deaconess Medical Center whose laboratory investigates topics highly relevant to the proposed project, including the development of novel antimicrobial susceptibility testing methods and the investigation of new therapeutics for CRE. Dr. Brennan-Krohn will be supported during the award period by an advisory committee that includes Dr. George Eliopoulos, a world-renowned expert on antimicrobial synergy. In the proposed project, Dr. Brennan-Krohn will initially test antimicrobial combinations against a comprehensive collection of clinical CRE isolates in order to establish combinatorial spectra of activity. For this part of the project, she will use an automated checkerboard array microdilution method that makes use of the HP D300 inkjet printer-based dispensing system. She will next develop a novel, fluorescent time-kill synergy assay in order to investigate the bactericidal kinetics of synergistic combinations. Finally, she will investigate the in vivo efficacy and PK/PD parameters of the most effective combinations using an immunocompromised mouse model of CRE infection. Ultimately, the enhanced understanding of synergy as well as the technology developed and validated during the proposed study are expected to inform the design of prospective clinical trials of combination antibiotic therapy and to establish simple, rapid synergy testing platforms that will for the first time provide synergy data that can be used in a clinically actionable timeframe to guide patient care.