A Far‐Red Fluorescent DNA Binder for Interaction Studies of Live Multidrug‐Resistant Pathogens and Host Cells

Transgene expression of green fluorescent protein (GFP) has facilitated the spatiotemporal investigation of host–pathogen interactions; however, introduction of the GFP gene remains challenging in drug‐resistant bacteria. Herein, we report a novel far‐red fluorescent nucleic acid stain, 6‐TramTO‐3 , which efficiently labels bacteria through a DNA binding mode without affecting growth and viability. Exemplarily, we stained Klebsiella pneumoniae, a major threat to hospitalized patients, and deciphered divergent interaction strategies of antibiotic‐resistant and antibiotic‐sensitive Klebsiella strains with immune cells. 6‐TramTO‐3 constitutes an off‐the‐shelf reagent for real‐time analysis of bacterial infection, including strains for which the use of genetically encoded reporters is not feasible. Eventually, our approach may aid the development of strategies to combat a major worldwide health threat: multidrug‐resistant bacteria.