Four different thermodynamic approaches were compared on their usefulness to predict correctly the adhesion of two fouling microogranisms from dairy processing to various solid substrata. The surface free energies of the interacting surfaces were derived from measured contact angles according to: 1. The equation of state; 2. The geometric-mean equation using dispersion and polar components neglecting spreading pressures; 3. The geometric-mean equation using dispersion and polar components while accounting for spreading pressures; and 4. The Lifshitz-van der Waals/Acid-Base approach. All approaches yielded similar surface free energies for the low energy surfaces. Application of approach 1 with different liquids did not give consistent values for the high surface free energy substrata. The dispersion or Lifshiftz-van der Waals components were nearly equal for approaches 2, 3, and 4; however, the polar or acid-base components differed greatly according to the approach followed. Approaches 1 and 2 correctly predicted that adhesion should occur, although the trend with respect to the various solid substrata was opposite the one experimentally observed, as was also the trend predicted by approach 4. Only approach 3 correctly predicted the observed bacterial adhesion with respect to the various solid substrata. In approach 3 and 4, adhesion was frequently found, despite a positive free energy of adhesion. This was attributed to either possible local attractive electrostatic interactions, inadequate weighing of surface free energy components in the calculation of free energies of adhesion, or to additional forces arising from structured interfacial water.

To characterize the functional cell surface, the zeta potentials and elemental surface composition of Streptococcus salivarius HB and a range of mutants with known molecular surface structures were determined. Zeta potentials of fully hydrated cells were measured as a function of pH in dilute potassium phosphate solutions, yielding isoelectric points of the strains. Elemental composition (0, C, N, and P) of the outer 2 to 5 nm of the freeze-dried cell surfaces were measured by X-ray photoelectron spectroscopy. An increasing loss of proteinaceous fibrillar surface antigens of the mutants was found to be accompanied by a progressive decrease in the N/C ratio from 0.104 in the parent strain HB to 0.053 in mutant HBC12. Simultaneously, the value of the isoelectric point shifted from 3.0 to 1.3. In a previous study (A. H. Weerkamp, H. C. van der Mei, and J. W. Slot, Infect. Immun. 55:438-455, 1987) on the cell surfaces of the same strains, it was shown that removal of fibrils led to increased exposure of (lipo)teichoic acid at the surface, which explains the low isoelectric point caused by the low pKa of the phosphate groups.The outer surface of bacterial cells mediates many crucial interactions of the cells with their environment, such as adherence, flocculation, antigenicity, susceptibility to phagocytosis, and binding of macromolecules. Understanding these complex functions requires detailed knowledge of the elemental, molecular, and structural composition of the cell surface, which is obviously different from the bulk of the cell wall (3, 18). Generally such knowledge is obtained by electron microscopic methods, by probing the cell surface with specific molecules such as antibodies or lectins, by functional tests such as hydrophobicity assays, or by indirect techniques involving the removal of surface components (8,12).Only a few techniques provide information on the chemical composition on the outer surface of intact cells. An elemental analysis over the thickness of the outer 2 to 5 nm can be obtained by X-ray irradiation of surfaces, causing ejection of electrons, which can be discriminated by their binding energy in a specific chemical element. X-ray photoelectron spectroscopy (XPS) is most frequently used for nonbiological surfaces but has been used in a few cases for the study of bacterial and eucaryotic cells (2, 7, 13). Compared with other surface techniques (1), XPS has the advantage of being nondestructive and highly surface sensitive; it gives a high information content and yields quantitative data on elemental composition and chemical bonding. A disadvantage, common to most analytical surface techniques, is that samples must be measured under high vacuum (10-6 to 10-9 Pa).Previously, we studied the structure and molecular composition of the cell surface of Streptococcus salivarius HB and a range of mutants devoid of specific fibrillar appendages and lacking adhesive abilities (11,17). No information is * Corresponding author. available on the elemental surface composition of these cells and how it w...

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Abstraet-Supcrhydrophohic FEP-Teflon was prepared by argon ion etching followed by oxygen glow discharge treatment of commercially available FEP-Teflon sheet material. This combined treatment yielded an increase in water contact angle from 109° to > 140°. Ion etching alone caused a small increase in surface roughness and a loss of fluorine from the surface, but the water contact angles increased only to 120°. Scanning electron micrographs of ion-etched surfaces showed stalky protrusions with a diameter of approximatcly 40 nm. Glow discharge treatment of ion-etched surfaces reduced the length of these protrusions and therewith the microscopic surface roughness. However, in all cases the macroscopic surface roughness was less than 1 um (RA value). X-Ray photoelectron spectroscopy indicated major changes in elemental surface composition as a result of the treatments. These modifications did not influence the infrared absorption spectra (attenuated total reflection) of the modified surfaces, indicating that the chemical changes brought about are really superficial. It is concluded that the superhydrophobicity created is mainly due to changes in the specific, microscopic surface topography resulting from ion etching, but also partly due to the role of the glow discharge treatment, restoring a high surface concentration of fluorine after ion etching.

The surface properties of nine Streptococcus mitis and four Peptostreptococcus micros strains from the oral cavity were examined and compared with a large group of oral streptococci. Zeta potential and contact angle measurements were employed to determine physico-chemical cell surface properties. In addition, elemental surface concentration ratios were obtained via X-ray photoelectron spectroscopy, and surface structures were examined with transmission electron microscopy. The S. mitis and P. micros strains were found to have higher isoelectric points, higher hydrophobicities and higher N/C surface concentration ratios than some other oral streptococci. The combined data suggest that both species possess large amounts of surface protein. All the S. mitis strains displayed abundant surface fibrils in negative staining, but the P. micros strains were devoid of surface appendages indicating that surface protein is present in different forms in the two species. The surfaces of S. mitis and P. micros type strains differed significantly from the other strains examined.