Effect of surfactants on the antibacterial activity of preservatives

Antibacterial activities of methyl-p-hydroxybenzoate, phenoxyethanol and chlorocresol against Pseudomonas aeruginosa were evaluated in the presence of varying concentrations of Tween 80. Below cmc level, the bactericidal activities increased with decrease in the surface tension values of Tween 80 solutions and with interfacial tension values of Tween 80 solution/liquid paraffin systems. Linear relationships were found to exist between the concentrations of each preservative required to reduce the microbial population by a factor 10(3) within 48 hours and the values of surface tension and interfacial tension respectively. Reduction in surface tension and interfacial tension would have increased the adsorption and uptake of preservatives by bacterial cells thereby killing the cells at a faster rate. Concentrations of Tween 80 above cmc also enhanced the antibacterial activities of these preservatives. This was attributed to the increase in the permeability of bacterial membranes to preservatives.