Determination of hydrophobicity on bacterial surfaces by nonionic surfactants

The hydrophobicity of the bacterial cell surface was determined by using nonionic surfactants. The method is based on the adsorption of nonionic surfactants at the hydrophobic sites of the cell surface. Among many nonionic surfactants, C18H37O(CH2CH2O)13H was preferred. The surfactant was added in excess to a bacterial suspension, and the suspension was mixed by sonication or mechanical stirring. The amount of surfactant remaining in the supernatant after centrifugation was determined spectrophotometrically by measuring the absorbance of tetrabromophenolphthalein ethylester. Effective dispersion of bacterial cells such as Staphylococcus aureus and Mycobacterium smegmatis was achieved by sonication in the presence of the nonionic surfactant. Adsorption measurements coincided with Langmuir's equation, indicative of monolayer adsorption. The method is useful for the determination of the hydrophobicity of various bacterial cell surfaces.