Nonionic Surfactants Enhancing Bactericidal Activity at Their Critical Micelle Concentrations

This is the authors' abstract. We don't add key points for this paper.

soybean-casein digest broth with lecithin and polysorbate 80 (SCDLP) containing Tween 80 is added to the solution.Subsequently, viable bacteria are incubated on the SCDLP plates.Viable bacteria are able to grow on these plates in the presence of residual bactericides.It has been suggested that bactericides are incorporated into micelles formed by nonionic surfactant molecules such as Tween 80, and the adsorption of bactericides into the bacteria is suppressed 5) .Alternatively, several nonionic surfactants show reductions in minimum inhibitory concentrations (MIC) of bactericides such as cationic surfactants 2,6) .Gomi et al. reported that particular nonionic surfactants augmented bactericidal activity of DDAC 7) .Certain bactericides are included in many recent types of cleaning products and their bactericidal ability has great value.Nonionic surfactants are also included in cleaning products to increase the washing performance 8, 9) .Methyl ester ethoxylates (MEE) are well-known ester type nonionic surfactants that have superior washing performance 10,11) .Abstract: Bactericidal activities of benzalkonium chloride [also known as alkyldimethylbenzylammonium chloride (ADBAC)] containing nonionic surfactants such as methyl ester ethoxylates (MEE) with the alkyl group C8-C14 and oxyethylene (EO) group of average adduct number 3-15 were measured against Escherichia coli and Staphylococcus aureus.Sample solutions containing MEE in the vicinity of the critical micelle concentration exhibited a dramatic decrease in viable bacterial counts.MEE with an alkyl group of C12 and an oxyethylene group of lower adduct number exhibited little viable bacterial counts than those having higher EO adduct numbers.MEE with reduced EO adduct numbers increased fluorescence intensity in E. coli using the viability stain SYTO 9. Our results show that MEE molecules with low EO adduct numbers exhibited bactericidal activity by increasing the permeability of the E. coli cell membrane.Sample solution containing ADBAC and MEE molecules with lower EO adduct numbers also displayed higher zeta potentials.Moreover, ADBAC molecules incorporated into micelles of MEE with lower EO adduct numbers were adsorbed onto the surface of E. coli, which augmented bactericidal activity.