Suppression of β-Lactam Resistance by Aspergillomarasmine A Is Influenced by both the Metallo-β-Lactamase Target and the Antibiotic Partner

Abstract

The rise of Gram-negative pathogens expressing metallo-β-lactamases (MBLs) is a growing concern, threatening the efficacy of β-lactam antibiotics, in particular, the carbapenems. There are no inhibitors of MBLs in current clinical use. Aspergillomarasmine A (AMA) is an MBL inhibitor isolated from <i>Aspergillus versicolor</i> with the ability to rescue meropenem activity in MBL-producing bacteria both <i>in vitro</i> and <i>in vivo</i> Here, we systematically explored the pairing of AMA with six β-lactam antibiotic partners against 19 MBLs from three subclasses (B1, B2, and B3). Cell-based assays performed with <i>Escherichia coli</i> and <i>Klebsiella pneumoniae</i> showed that bacteria producing NDM-1 and VIM-2 of subclass B1 were the most susceptible to AMA inhibition, whereas bacteria producing CphA2 and AIM-1 of subclasses B2 and B3, respectively, were the least sensitive. Intracellular antibiotic accumulation assays and <i>in vitro</i> enzyme assays demonstrated that the efficacy of AMA/β-lactam combinations did not correlate with outer membrane permeability or drug efflux. We determined that the optimal β-lactam partners for AMA are the carbapenem antibiotics and that the efficacy of AMA is linked to the Zn²⁺ affinity of specific MBLs.