Nonionic surfactants enhancing bactericidal activity at their critical micelle concentrations

Area of Science:

• Microbiology
• Surface Chemistry
• Biophysics

Background:

• Benzalkonium chloride (ADBAC) is a common disinfectant.
• Nonionic surfactants, such as methyl ester ethoxylates (MEE), can modify the properties of disinfectants.
• Understanding how MEE affects ADBAC's bactericidal activity is crucial for developing effective antimicrobial agents.

Purpose of the Study:

• To investigate the bactericidal activity of benzalkonium chloride (ADBAC) combined with methyl ester ethoxylates (MEE).
• To determine the influence of MEE's alkyl chain length and oxyethylene (EO) adduct number on antimicrobial efficacy against Escherichia coli and Staphylococcus aureus.
• To elucidate the mechanism of action for enhanced bactericidal activity.

Main Methods:

• Bactericidal activity assays were performed against E. coli and S. aureus using ADBAC-MEE mixtures.
• Critical micelle concentration (CMC) and zeta potential measurements were conducted.
• Bacterial membrane permeability was assessed using the viability stain SYTO 9 and fluorescence intensity measurements.

Main Results:

• MEE, particularly near its CMC, significantly reduced viable bacterial counts.
• MEE with a C12 alkyl group and lower EO adduct numbers showed greater bactericidal efficacy.
• Reduced EO adduct numbers in MEE increased E. coli membrane permeability and fluorescence intensity.
• ADBAC-MEE mixtures with lower EO adduct numbers exhibited higher zeta potentials and enhanced bacterial surface adsorption.

Conclusions:

• MEE molecules with low EO adduct numbers enhance ADBAC's bactericidal activity by increasing bacterial cell membrane permeability.
• The combination of ADBAC and MEE with specific properties offers a potent antimicrobial strategy.
• Surface adsorption of ADBAC onto MEE micelles contributes to augmented bactericidal effects.