<i>In Vitro</i> and <i>In Vivo</i> Activities of β-Lactams in Combination with the Novel β-Lactam Enhancers Zidebactam and WCK 5153 against Multidrug-Resistant Metallo-β-Lactamase-Producing Klebsiella pneumoniae

Abstract

Zidebactam and WCK 5153 are novel bicyclo-acyl hydrazide (BCH) agents that have previously been shown to act as β-lactam enhancer (BLE) antibiotics in <i>Pseudomonas aeruginosa</i> and <i>Acinetobacter baumannii</i> The objectives of this work were to identify the molecular targets of these BCHs in <i>Klebsiella pneumoniae</i> and to investigate their potential BLE activity for cefepime and aztreonam against metallo-β-lactamase (MBL)-producing strains <i>in vitro</i> and <i>in vivo</i> Penicillin binding protein (PBP) binding profiles were determined by Bocillin FL assay, and 50% inhibitory concentrations (IC₅₀s) were determined using ImageQuant TL software. MICs and kill kinetics for zidebactam, WCK 5153, and cefepime or aztreonam, alone and in combination, were determined against clinical <i>K. pneumoniae</i> isolates producing MBLs VIM-1 or NDM-1 (plus ESBLs and class C β-lactamases) to assess the <i>in vitro</i> enhancer effect of BCH compounds in conjunction with β-lactams. Additionally, murine systemic and thigh infection studies were conducted to evaluate BLE effects <i>in vivo</i> Zidebactam and WCK 5153 showed specific, high PBP2 affinity in <i>K. pneumoniae</i> The MICs of BLEs were >64 μg/ml for all MBL-producing strains. Time-kill studies showed that a combination of these BLEs with either cefepime or aztreonam provided 1 to >3 log₁₀ kill against MBL-producing <i>K. pneumoniae</i> strains. Furthermore, the bactericidal synergy observed for these BLE-β-lactam combinations translated well into <i>in vivo</i> efficacy even in the absence of MBL inhibition by BLEs, a characteristic feature of the β-lactam enhancer mechanism of action. Zidebactam and WCK 5153 are potent PBP2 inhibitors and display <i>in vitro</i> and <i>in vivo</i> BLE effects against multidrug-resistant (MDR) <i>K. pneumoniae</i> clinical isolates producing MBLs.