Subcellular chemical imaging of antibiotics in single bacteria using C60-secondary ion mass spectrometry

The inherent difficulty of discovering new and effective antibacterials and the rapid development of resistance particularly in Gram-negative bacteria, illustrates the urgent need for new methods that enable rational drug design. Here we report the development of 3D imaging cluster secondary ion mass spectrometry (SIMS) as a label-free approach to chemically-map small molecules in aggregated and single Escherichia coli cells, with ~300 nm spatial resolution and high chemical sensitivity. The feasibility of quantitative analysis was explored, and a non-linear relationship between treatment dose and signal for tetracycline and ampicillin, two clinically-used antibacterials, was observed. The methodology was further validated by the observation of reduction in tetracycline accumulation in an E. coli strain expressing the tetracycline-specific efflux pump (TetA) compared to the isogenic control. This study serves as a proof-of-concept for a new strategy for chemical imaging at the nano-scale and has the potential to aid discovery of new antibacterials