Sensitive Detection of Broad-Spectrum Bacteria with Small-Molecule Fluorescent Excimer Chemosensors

Abstract

Antibiotic resistance is a major problem for world health, triggered by the unnecessary usage of broad-spectrum antibiotics on purportedly infected patients. Current clinical standards require lengthy protocols for the detection of bacterial species in sterile physiological fluids. In this work, a class of small-molecule fluorescent chemosensors termed <i>ProxyPhos</i> was shown to be capable of rapid, sensitive, and facile detection of broad-spectrum bacteria. The sensors act via a turn-on fluorescent excimer mechanism, where close-proximity binding of multiple sensor units amplifies a red shift emission signal. <i>ProxyPhos</i> sensors were able to detect down to 10 CFUs of model strains by flow cytometry assays and showed selectivity over mammalian cells in a bacterial coculture through fluorescence microscopy. The studies reveal that the zinc(II)-chelates cyclen and cyclam are novel and effective binding units for the detection of both Gram-negative and Gram-positive bacterial strains. Mode of action studies revealed that the chemosensors detect Gram-negative and Gram-positive strains with two distinct mechanisms. Preliminary studies applying <i>ProxyPhos</i> sensors to sterile physiological fluids (cerebrospinal fluid) in flow cytometry assays were successful. The results suggest that <i>ProxyPhos</i> sensors can be developed as a rapid, inexpensive, and robust tool for the "yes-no" detection of broad-spectrum bacteria in sterile fluids.