Antimicrobial resistance is an urgent threat to human health, and new antibiotics are desperately needed, as are research tools to aid in their discovery and development. Vancomycin is a glycopeptide antibiotic that is widely used for the treatment of Gram-positive infections1. However, the effectiveness of vancomycin is under threat due to the development of resistance2. Fluorescent probes can be used to visualise cellular structure and dynamics in living cells enabling scientists to understand how antibiotics interact with bacteria3. Here, we describe the synthesis of novel vancomycin probes and demonstrate their utility in studying interactions between antibiotic and bacteria.
Methods
Vancomycin probes were synthesized by a facile Cu-catalysed azide−alkyne cycloaddition reaction. They were then used to visualise bacteria using high-resolution microscopy, flow cytometry and fluorescence spectrophotometry.
Results
We synthesised colorful vancomycin probes which retained similar antibacterial activity as the parent antibiotic, vancomycin. Microscopy of Staphylococcus aureus stained with these probes showed strong fluorescent localisation at the dividing septum compared to the lateral wall, confirming binding to the nascent peptidoglycan Lipid II. These target-specific probes did not normally label Gram-negative Escherichia coli due to the impermeable outer membrane (OM), but if the OM was permeabilised by genetic modifications, cold stress, or membrane-active antibiotics, fluorescent uptake could quantify the OM damage.
Conclusion
Vancomycin fluorescent probes were synthesised. We highlighted their versatility at visualising bacteria and determining OM permeabilisation in Gram-negative bacteria. These probes could become useful tools to help define the mechanism of action of new antimicrobial compounds and the effects of bacterial pathway mutations.