Whole-Cell Bioreporter-Based Assay for Detecting Fungal-Derived β-Lactamase Inhibitors

β-lactams are an important family of antibiotics that are prone to undergo resistance inhibition though the production of β-lactamases by some microorganisms. To combat this resistance and preserve the efficacy of β-lactam antibiotics, we developed a strategy for the discovery of such β-lactamase inhibitors. When combined with β-lactams, these inhibitors allow the antibiotics to be effective and prevent resistance. To date, the development of such combinatory drugs is limited due to the complexity of screening for new β-lactamase inhibitors. Therefore, to facilitate this development, it was essential to find sensitive assays to effectively screen for lactamase inhibitory compounds. To this end, a novel bioassay utilizing bioluminescent indicator bacteria as bioreporters was developed. The assay was first optimized using commercial antibiotics together with known β-lactamase inhibitors. Using this bioassay, we then screened for novel natural β-lactamase inhibitors derived from coral-associated fungi. We showed that the fungus Penicillium spinulosum, originating from the coral Pocillopora sp. from the Gulf of Aqaba Eilat, produced compounds with anti-β-lactamase activity. We further demonstrated that the bioreporter bacteria used here responded to the combined antibiotics and β-lactamase inhibitors in a concentration-dependent manner, indicating their usefulness for β-lactamase-inhibiting compound discovery. Future structural identification will promote the validation of this assay's usefulness.