Effect of Salt on Synthetic Cationic Antimicrobial Polymer-Cell Interactions

Area of Science:

• Antimicrobial agents
• Microbiology
• Polymer science

Background:

• Cationic antiseptics are widely used in diverse environments with varying salinity.
• The impact of salt concentration on antiseptic efficacy is not fully understood.

Purpose of the Study:

• To investigate how sodium chloride (NaCl) concentration affects the antimicrobial activity of polydiallyldimethylammonium chloride (PDADMAC).
• To elucidate the mechanism by which PDADMAC interacts with Escherichia coli (E. coli) under different salinity conditions.

Main Methods:

• Utilized fluorescence microscopy to monitor PDADMAC adsorption onto E. coli and assess cell viability.
• Employed fluorescence depolarization to measure changes in model membrane rigidity.

Main Results:

• Increased NaCl concentrations reduced PDADMAC adsorption density and antimicrobial efficacy.
• At 0.15 M NaCl or higher, PDADMAC inhibited E. coli growth and reproduction without causing cell death, a effect reversible upon PDADMAC removal.
• Salt decreased the membrane rigidifying effect of PDADMAC.

Conclusions:

• Salinity significantly modulates the interaction between cationic antiseptics and bacteria.
• The observed growth inhibition is attributed to reversible polymer bridging on the cell surface, hindering membrane expansion.