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The monobactam LYS228: mode of action and mechanisms decreasing in vitro susceptibility of Escherichia coli and Klebsiella pneumoniae

Dean, Charles and Barkan, Dave and Bermingham, Alun and Blais, Johanne and Casey, Fergal and Casarez, Anthony and Colvin, Richard and Fuller, John and Jones, Adriana and Li, Cindy and Lopez, Sara and Metzger Iv, Louis and Mostafavi, Mina and Prathapam, Ramadevi and Rasper, Dita and Reck, Folkert and Ruzin, Alexey and Shaul, Jacob and Shen, Xiaoyu and Simmons, Robert and Skewes-Cox, Peter and Takeoka, Ken and Tamrakar, Pramila and Uehara, Tsuyoshi and Wei, Jun-Rong (2018) The monobactam LYS228: mode of action and mechanisms decreasing in vitro susceptibility of Escherichia coli and Klebsiella pneumoniae. Antimicrobial Agents and Chemotherapy, 62 (10). ISSN 1098-6596


The monobactam chemical scaffold is attractive for the development of new agents to treat infections caused by drug-resistant Gram-negative bacteria since it is stable to metallo-β-lactamases (MBLs). However, the clinically used monobactam aztreonam lacks stability to serine β-lactamases (SBLs) that are often co-expressed with MBLs. The novel monobactam LYS228 is stable to MBLs and most SBLs. LYS228 bound purified Escherichia coli penicillin binding protein 3 (PBP3) similarly to ATM (k2/Kd = 367504 s-1M-1 and 409229 s-1M-1, respectively) according to stopped-flow fluorimetry. A gel-based PBP binding assay showed that LYS228 bound mainly to E. coli PBP3, with weaker binding to PBP1a and PBP1b. Exposing E. coli cells to LYS228 caused filamentation, consistent with cell division defects resulting from inhibition of PBP3. No single-step mutants were selected from twelve Enterobacteriaceae strains expressing different classes of β-lactamases at 8X the minimum inhibitory concentration (MIC) of LYS228 (frequency <2.5x10-9). At 4X the MIC, mutants were selected from two of twelve strains at frequencies of 1.8x10-7 and 4.2x10-9. LYS228 MICs were ≤ 2 μg/mL against all mutants. These frequencies compared favorably to those obtained with meropenem and tigecycline. Mutations decreasing LYS228 susceptibility occurred in ramR and cpxA (Klebsiella pneumoniae) and baeS (E. coli and K. pneumoniae). Susceptibility of E. coli ATCC 25922 to LYS228 decreased 256-fold (MIC 0.125 to 32 µg/mL) after 20 serial passages. Mutants had accumulated mutations in ftsI (encoding the target, PBP3), baeR, acrD, envZ, sucB and rfaI. These results support the continued development of LYS228, which is currently undergoing Phase II clinical trials for complicated intraabdominal infection and complicated urinary tract infection ( NCT03354754).

Item Type: Article
Date Deposited: 28 Aug 2018 00:45
Last Modified: 28 Aug 2018 00:45


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