A comparison of various methods to determine hydrophobic properties of streptococcal cell surfaces

In order to determine whether various methods which are commonly applied to determine the hydrophobicity of bacterial cell surfaces yield similar results, the hydrophobicity of a range of oral streptococcal isolates was measured using various methods including adsorption to hexadecane, hydrophobic interaction chromatography, salt-aggregation and contact angle measurements. In addition the zela potential and the adhesion to saliva-coated hydroxyapatite were determined. To compare the results of the different methods, linear and rank correlation coefficients were calculated. The resulting correlations were weak when applied to the whole range of strains even in those cases where the tests are expected to probe the same surface characteristics. However, generally good correlations were obtained when a set of strains was examined which were derived from a single parent strain and which only differed in defined surface structures. Accordingly it must be concluded from the methods applied here, that if is not possible to define the surface ‘hydrophobicity’ of a bacterium other than on a comparative level with closely related strains. No clear correlation was found between any hydrophobicity test and the adhesion to saliva-coated hydroxyapatite.