Schematic showing the principle of the β-LEAF assay. A. The β-LEAF probe comprises a β-lactam core structure including the cleavable lactam ring (green), flanked by two fluorophores (encircled), which undergo static quenching when the probe is intact. Following cleavage by β-lactamase, the fluorophores move apart and show fluorescence. B. Assay profile for β-lactamase producing bacteria C. Assay profile for lactamase non-producing bacteria.