Intracellular\nQuantification of an Antibiotic Metal\nComplex in Single Cells of Escherichia coli Using Cryo-X-ray Fluorescence Nanoimaging

Bacterial resistance\nis a major public health challenge. In Gram-negative\nbacteria, the synergy between multidrug efflux pumps and outer membrane\nimpermeability determines the intracellular concentration of antibiotics.\nConsequently, it also dictates antibiotic activity on their respective\ntargets. Previous research has employed spectrofluorimetry and synchrotron\nradiation-based DUV microscopy as tools for monitoring the accumulation\nof fluoroquinolone antibiotics in bacteria at population and single-cell\nscales, respectively. Here, we show that cryo-XRF nanoimaging allows\nintracellular localization and quantification of a fluoroquinolone\nmetal complex accumulation in Escherichia coli with different efflux pump expression levels. This method offers\na promising avenue for elucidating the intracellular behavior of a\nrange of metallodrugs in bacteria and for designing novel agents with\nunique mechanisms of action.