Cluster analysis of genotypically characterized Lactobacillus species based on physicochemical cell surface properties and their relationship with adhesion to hexadecane

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Abstract
Lactobacilli can interfere with the adhesion of uropathogens to uroepithelial cells and catheter materials through a variety of mechanisms, such as adhesion. Lactobacillus adhesion to substratum surfaces has been theorized to result from the physicochemical properties of the interacting surfaces. In this paper physicochemical cell-surface properties, including hydrophobicity (determined by water contact angles), pH dependence of zeta potentials, elemental surface composition (determined by X-ray photoelectron spectroscopy), and adhesion to hexadecane, of four genotypically characterized Lactobacillus species (eight L. acidophilus, eight L. casei, four L. fermentum, and seven L. plantarum strains) were determined to see whether a grouping of the strains according to their phenotypes could be obtained that corresponded with the genotypic characterization of the strains. The strains showed major differences in physicochemical cell-surface properties: at the species level relationships could be observed between water contact angles, isoelectric points, and the N/C and O/C elemental surface concentration ratios, with nitrogen-containing groups (proteins) being responsible for increased hydrophobicities and isoelectric points, and oxygen-containing groups (phosphates and polysaccharides) yielding decreased hydrophobicities and isoelectric points. A hierarchical cluster analysis grouped all L. acidophilus strains in one well-separated cluster that also included two L. casei and two L. fermentum strains. Separation of L. acidophilus from the other species was done predominantly on the basis of increased cell surface hydrophobicity (average water contact angle of 63°) and isoelectric point (approximately pH 3.3) as compared with the other species, which had lower water contact angles and isoelectric points, and corresponded with the observation that only L. acidophilus strains adhered in measurable numbers to hexadecane. Also, the L. plantarum strains were grouped closely together in one cluster, but this cluster was heterogeneous due to the inclusion of L. casei and L. fermentum strains.Key words: Lactobacillus, surface properties, hydrophobicity, zeta potential, adhesion.

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