Time-Resolved Killing of Individual Bacterial Cells by a Polycationic Antimicrobial Polymer

Area of Science:

• Microbiology
• Polymer Science
• Antimicrobial Research

Background:

• Polycationic polymers are common antiseptics, with efficacy typically measured by Minimum Bactericidal Concentration (MBC).
• Traditional methods assess bulk cell population responses, overlooking individual cell variations.
• Understanding antimicrobial variability is crucial for developing effective treatments.

Purpose of the Study:

• To investigate the heterogeneity in individual bacterial cell responses to a polycationic antimicrobial.
• To correlate antimicrobial adsorption with cell death kinetics at the single-cell level.
• To compare responses across different bacterial species (Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa).

Main Methods:

• Utilized fluorescence microscopy to track labeled polydiallyldimethylammonium chloride (PDADMAC) adsorption onto individual bacterial cells.
• Employed a cell permeability indicator to monitor cell death over time for each bacterium.
• Applied time-lapse microscopy to observe ensemble behavior of bacterial populations under antimicrobial exposure.

Main Results:

• Significant variability in PDADMAC adsorption and time-to-death was observed among individual cells, even within monoclonal populations.
• Cell death typically occurred after a threshold PDADMAC adsorption was reached, with a 5-10 minute lag time.
• Individual cell death time strongly correlated with its specific PDADMAC adsorption rate.
• Antimicrobial adsorption and cell death kinetics varied by species, correlating with cell surface charge.

Conclusions:

• Single-cell analysis provides critical insights into antimicrobial efficacy that are missed by traditional ensemble measurements.
• Bacterial cell response to polycationic antimicrobials is highly heterogeneous.
• Adsorption rate and cell surface properties significantly influence individual bacterial susceptibility and death kinetics.