1642. A Novel β-lactamase Inhibitor (Durlobactam, DUR) and β-Lactams Enhance Susceptibility Against Multidrug-Resistant (MDR) Mycobacterium abscessus (Mab)

BACKGROUND: Mab is a MDR nontuberculous mycobacterium that causes lung infections in patients with structural lung disease. Mab harbors a chromosomally encoded class A β-lactamase, Bla(Mab), able to hydrolyze penicillins, cephalosporins and carbapenems. L,D- and D,D-transpeptidases (L,D TP and D,D TP) shape peptidoglycan (PG) synthesis and contribute to cell wall structure. Select combinations of β-lactams that inhibit L,D TP and D,D TPs and Bla(Mab) are desirable as they can potentially improve treatment outcomes. DUR is a novel DBO β-lactamase inhibitor (BLI) with broad-spectrum activity against Ambler class A, C, and D β-lactamases (Fig.). Here, we investigated the mechanism of action and efficacy of DUR alone and combined with select β-lactams in restoring susceptibility of Mab to β-lactam antibiotics METHODS: Minimum inhibitory concentrations (MICs) of cefuroxime (CEF), imipenem (IMI) and amoxicillin (Amox) with or without DUR were determined using microdilution. Approximately 5 x 10(5) colony-forming units per milliliter were inoculated into Middlebrook 7H9 Broth supplemented with 10% (vol/vol) oleic albumin dextrose catalase and 0.05% (vol/vol) Tween 80. When more than 2 drugs were combined, Amox was added at fixed concentration of 8 µg/ml to serial dilutions of CEF-DUR or IMI-DUR. Mab isolates were incubated with test agents at 30°C for 48 h, and MIC was defined as lowest antibiotic concentration that prevented visible bacterial growth. Reaction intermediates in the inactivation pathway of Bla(Mab,) L,D-TP and D,D-TPs with DUR RESULTS: One hundred clinically derived and previously characterized isolates were tested in these assays. MIC(50) and MIC(90) of DUR alone was 4 and 8 µg/ml, demonstrating intrinsic activity. Combinations of DUR-IMI or DUR-CEF plus 8 µg/mL Amox lowered MIC(50) to < 0.06 µg/ml in all 100 clinical isolates (Table). Mass spectrometry analyses of Bla(Mab), L,D-TP and D,D-TPs (Mab (2,4)) inactivated by DUR showed formation of stable adducts of DUR to Bla(Mab), L,D-TP and D,D-TPs (Fig.) Chemical composition of durlobactam (DUR) and mass spectrometry of BlaMab, L,D TP and D,D TPs incubated with DUR [Image: see text] MIC50 and MIC90 of 100 Mab clinical strains against DUR alone and in combination with Amox, CEF and IMI [Image: see text] CONCLUSION: We demonstrate that a novel DBO BLI, DUR, is an active agent with potent intrinsic activity against Bla(Mab) and Mab L,D-TPs and D,D-TPs. We hypothesize that DUR improves b-lactam activity by protecting against the hydrolytic activity of Bla(Mab) and by targeting multiple steps in PG synthesis DISCLOSURES: Alita Miller, PhD, Entasis Therapeutics (Employee) Robert A. Bonomo, MD, Entasis, Merck, Venatorx (Research Grant or Support)