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Co-aggregation (interactions between two suspended micro-organisms) between oral microbial pairs has been studied extensively and is believed to be an important factor in dental plaque formation. However, co-adhesion (interactions between suspended and already-adhering micro-organisms) may well be equally important. The aim of this paper was to determine the influence of saliva and lactose on the co-adhesion of streptococci (S. oralis 34 and S. sanguis PK1889) to actinomyces (A. naeslundii T14V-J1 or 5951) adhering on glass under flow from buffer and saliva in the absence and presence of lactose. The kinetics of co-adhesion as well as co-adhesion in a stationary end-point of co-aggregating and non-co-aggregating pairs was studied in a parallel plate flow chamber by analysis of the spatial arrangement of co-adhering micro-organisms as a function of time. For co-aggregating pairs, initial deposition rates of streptococci in the immediate vicinity of adhering actinomyces (local initial deposition rates) were up to 5 to 10 times higher than the non-local initial deposition rates in buffer and in saliva, respectively. In a stationary end-point of co-adhesion, 5 to 6 times more streptococci co-adhered with the adhering actinomyces than averaged over the entire substratum surface. A non-co-aggregating pair showed only minor preferential (co-)adhesion near the adhering actinomyces. Co-adhesion in buffer was fully lost when lactose was added. However, addition of lactose to saliva did not inhibit co-adhesion, but co-adhesion became more reversible. Detachment of micro-organisms from the substratum due to the passage of an air-liquid interface, as occurs in the oral cavity during eating, drinking, and speaking, was minimal when deposition was carried out from buffer to bare glass. Major detachment of streptococci adhering to the substratum occurred when adhesion was mediated through a salivary conditioning film on the glass, while detachment of adhering actinomyces and streptococci co-adhering with them remained low. It is suggested that, in the development of dental plaque, adhering actinomyces may act as strongholds for other micro-organisms, like streptococci, to adhere.

The fungal hydrophobin SC3p, a protein secreted by Schizophyllum commune, has become known to form SDS-insoluble layers and to change the physico-chemical properties of an interface. In this study, the surface activity of SC3p was studied by determining the interfacial tensions gamma iv and gamma sl during adsorption of SC3p at both the liquid-vapour and the solid-liquid interface utilizing the in situ technique axisymmetric drop-shape analysis by profile. To this end, protein solution droplets were put on the solid fluoroethylene-propylene-Teflon. At the liquid-vapour interface, SC3p caused a large decrease of gamma iv from 72 to 43 mJ m-2 at the concentration of 0.1 mg ml-1. At the solid-liquid interface, gamma sl was slightly decreased, whereas the contact angle theta increased, indicating an increase in hydrophobicity of FEP-Teflon, which is unique among the proteins studied so far. Earlier findings indicated a decrease in hydrophobicity of Teflon upon adsorption of SC3p, but this was after a washing and drying step. In order to reconcile these findings with those of the present study, adsorption of SC3p to hydrophobic surfaces is suggested to occur in bilayers. The second layer is supposed to be less strongly adsorbed than the first layer and can be easily removed by washing.

In this study, adhesion and spreading of human skin fibroblasts on gradient surfaces of dichlorodimethylsilane (DDS) coupled to glass was investigated. Gradient surfaces were prepared by the diffusion technique and characterized by the Wilhelmy plate technique and characterized by the Wilhelmy plate technique for their wettability and by scanning x-ray photoelectron spectroscopy for their chemical surface composition. A linear relation between the gradient length, based on advancing water contact angles, and the square root of the diffusion time of DDS was observed. XPS analysis and the cellular experiments were carried out on gradient surfaces prepared using a diffusion time of 3 h. A continuously varying chemical composition with Si/O elemental surface concentration ratio being highest on the hydrophobic end of the gradient surfaces. In the presence of serum proteins, human skin fibroblasts seeded on these gradient surfaces showed a preferential adhesion onto the steepest part of the gradient, probably due to an optimal local wettability and/or local chemistry. Furthermore, it was shown that the spread area of human fibroblasts increased over the length of the gradient surface when going from the hydrophobic to the hydrophilic end. Summarizing, this study shows that the use of gradient surfaces to study cellular responses to materials surface properties, like wettability, yields more-convincing conclusions than the use of a variety of materials with different wettabilities due to the control of the specific surface chemistry of gradient surfaces.

Objectives: The ability of three oral bacteria to adhere to hydrophobic amalgam (water contact angle 60 degrees) and hydrophobic resin composites (Prisma-AP.H 56 degrees. Herculite XRV 82 degrees and Z100 89 degrees) was compared using an in vitro assay., Methods and Results: Following preincubation of the materials with human saliva, X-ray photoelectron spectroscopy showed the surfaces to adsorb carbon and nitrogen-containing compounds in a conditioning film that appeared to block the detection of Na and others in 2100 resin. Hg and Ag in amalgam, Si and Zn in Prisma AP.H resin and Ag and Na in Herculite resin. The precoating of the substrata by a proteinaceous conditioning film led to decreased binding of viable cells of Streptococcus sanguis CH3, Streptococcus salivarius HB and Actinomyces viscosus WG as compared with the adhesion to bare composites. With and without salivary coating, there was a correlation between increased bacterial hydrophobicity and increased retention on the substrata. However, there was no statistical difference in binding to the amalgam compared with the resin composites. In vitro studies showed that the bacteria autoaggregated in the presence of saliva., Conclusion: The results indicate the potential ability of normal oral flora to colonize resin composite.

This paper presents a hypothesis on the importance of initial microbial adhesion in the overall process of biofilm formation. The hypothesis is based on the realization that dynamic shear conditions exist in many environments, such as in the oral cavity, or on rocks and ship hulls. Recognizing that an entire biofilm is detached during high shear once the bond between the initially adhering organisms and a surface (often constituted through a so-called 'conditioning film') is broken, it becomes clear that research should focus on detachment rather than adhesion. Experiments were done in a parallel plate flow chamber in which attempts were made to detach adhering oral streptococci from glass by applying a high shear caused by the passage of a bubble, giving an air-liquid interface. Detachment of streptococci from bare glass and from an initially adhering actinomycete strain appeared not to occur. However, substantial detachment of adhering streptococci occurred when adhesion was mediated through a salivary conditioning film, presumably because of cohesive failure in the conditioning film.

In this study, the effect of antibody adsorption on physicochemical properties of Streptococcus sobrinus was studied. Bacteria were preincubated with polyclonal antibodies or with OMVU10, a monoclonal antibody (MAb) reactive with S. sobrinus. The zeta potentials and the hydrophobicity as determined by microbial adhesion to hydrocarbons were measured in potassium phosphate buffer with a pH ranging from 2 to 9. S. sobrinus preincubated with polyclonal antibodies was positively charged at pH 2, 3, and 4 and had an isoelectric point at pH 4.8. Untreated S. sobrinus cells or cells preincubated with MAbs were negatively charged over the whole pH range. X-ray photoelectron spectroscopy showed a decrease in O/C and P/C ratios for bacteria preincubated with polyclonal antibodies. A combination of the pH-dependent zeta potential and the X-ray photoelectron spectroscopy data of the overall chemical composition of the cell surface suggests that polyclonal antibody adsorption occurs through blocking of surface phosphate. The measurement of hydrophobicity by microbial adhesion to hydrocarbons revealed that S. sobrinus preincubated with polyclonal antibodies was hydrophobic (90% of the bacteria bound to hexadecane), whereas the controls were relatively hydrophilic. S. sobrinus preincubated with OMVU10 was found to be more hydrophobic than the controls at pH 5 and 7. Hydrophobicity as measured by water contact angles showed an increase in hydrophobicity when S. sobrinus was preincubated with polyclonal antibodies. The epitopes to which the antibodies are directed were visualized by immunogold labeling and electron microscopy. The results suggested that OMVU10 is reactive with only a few epitopes of the cell surface, whereas polyclonal antibodies were found to be reactive with many epitopes. In conclusion, adsorption of polyclonal antibodies was found to influence the overall physicochemical surface properties of the organism, probably by forming a coating over the whole cell surface. Adsorption of MAbs was more localized, which could explain their lesser influence on these surface properties.

Under clinical conditions, during antibiotic treatment, micro-organisms often grow at sub-inhibitory concentrations. This may lead to altered adhesive cell surface properties and to a disruption of the indigenous microflora, in addition to the creation of a more pathogenic biofilm. The effects of growing Staphylococcus epidermidis, Escherichia coli and lactobacilli in the presence of sub-inhibitory concentrations of ciprofloxacin and vancomycin were determined. Growing the cells under antibiotic burden sometimes led to altered cell surface hydrophobicity (by adhesion to hexadecane), changes in the pH-dependence of zeta potentials, and elemental surface compositions or in different SDS-PAGE protein profiles. For several isolates only one of the surface properties was altered by the presence of an antibiotic in the growth medium and no systematic effects were observed for all isolates representing a certain species or even strain. The important conclusion to be drawn from the results of this study is that the effects of growing cells under antibiotic burden on their adhesive cell surface properties can only be established when using a variety of techniques.

In this study, human umbilical vein and human saphenous vein endothelial cells were seeded on glass and exposed to fluid shear in a parallel-plate flow chamber. Cell retention, morphology and migration were studied as a function of shear stress and of adhesion time prior to exposure to shear. Three-hour and 24-h adhesion times gave rise to comparable cell retention values after 2 h of flow for both cell types. Cell retention decreased from 85 to 20% as shear stress increased from 88 to 264 dynes cm-2 (8.8 to 26 Pa). Mean spreading areas decreased after the onset of flow, but subsequently stabilized to plateau values, which were smaller at higher shear stresses. Shape factors increased faster to higher values as cells were exposed to higher shear stresses, without any obvious preference in orientation of the cells with respect to the direction of flow. Migration was unidirectional with flow and linear with time. Migration was faster for cells which had adhered for 24 h than for cells which had adhered for 3 h and was accompanied by the presence of fibrillar structures left behind on the surface upstream of migrating cells. It is concluded that after 3 h adhesion to glass, cells have adhered with an adhesion strength that does not substantially increase during the next 21 h. However, during this time changes in cell-substratum interactions seem to occur judging by the differences in, e.g., migration rates.

The hydrophobin SC3p of Schizophyllum commune self-assembles into a 10-nm-thick amphipathic membrane at hydrophilic-hydrophobic interfaces. X-ray photoelectron spectroscopy of the hydrophobic membrane side of SC3p, assembled in vitro, showed an atomic composition similar to the calculated composition of SC3p when glycosylation was taken into account. The atomic composition measured at the hydrophilic membrane side deviated from that at the hydrophobic side and indicated the presence of a lower number of peptide bonds. High levels of S and N were detected only on mycelia carrying hydrophobic aerial hyphae, as expected with assembled SC3p present at the surface of these hyphae.

The displacement of Enterococcus faecalis 1131 from hydrophobic and hydrophilic substrata by isolates of Lactobacillus casei 36 and Streptococcus hyointestinalis KM1 was studied in a parallel plate flow chamber. The experiments were conducted with either 10 mM potassium phosphate buffer or human urine as the suspending fluid, and adhesion and displacement were measured by real-time in situ image analysis. The results showed that E. faecalis 1131 was displaced by lactobacilli (31%) and streptococci (74%) from fluorinated ethylene propylene in buffer and that displacement by lactobacilli was even more effective on a glass substratum in urine (54%). The passage of an air-liquid interface significantly impacted on adhesion, especially when the surface had been challenged with lactobacilli (up to 100% displacement) or streptococci (up to 94% displacement). These results showed that the parallel plate flow system with real-time in situ image analysis was effective for studying bacterial adhesion and that uropathogenic enterococci can be displaced by indigenous bacteria.

Thirteen strains of lactobacilli were tested for their ability to adhere to commercial devices used in the urinary tract. Although it appeared that the most hydrophilic organisms adhered in highest numbers, there was no significant correlation between water contact angle and adhesiveness to catheters. Five organisms tested were found to be highly adherent to Huggies commercial diapers. Loss in hydrophobicity upon serial culture of Lactobacillus fermentum B-54 was not due to a proteinaceous S layer, although protein involvement per se cannot be ruled out. It was evident that, not only can members of the normal female urogenital flora adhere to commonly used commercial prostheses, but their ability to attach is related to hydrophilic as well as hydrophobic surface components.

Silicone rubber voice prostheses are implants which are inserted in a non-sterile environment and therefore become quickly colonized by micro-organisms. The micro-organisms exist on the medical grade silicone rubber as mixed biofilms of bacteria and yeasts. A total of 79 bacterial and 39 yeast strains were isolated from these biofilms by soft ultrasonic treatment. Gram-positive/catalase-negative and Gram-positive/catalase-positive cocci represented the dominant bacterial strains. The yeasts were mainly Candida species. Further characterization of cell surface properties such as hydrophobicity by microbial adhesion to hexadecane and electrophoretic mobility showed a distinct difference when the bacterial strains were compared with the yeasts. The bacterial hydrophobicities ranged from 0 to 100% adhesion to hexadecane, whereas the yeast strains, especially the Candida albicans strains, all had markedly hydrophilic cell surfaces. A comparison of the electrophoretic mobilities showed also differences between bacteria and yeast. The values for the bacteria were found to be between -2.5 to -0.5 (10(-8) m2 V-1 s-1), whereas for the yeasts electrophoretic mobilities were more positive. Based on the adhesive properties of the isolated micro-organisms, strategies can now be developed to modify the properties of the silicone rubber to reduce biofilm formation on such prostheses.

The influence of surface free energy on supra- and subgingival plaque microbiology was examined in 9 patients with functional fixed prostheses supported by endosseous titanium implants. Two abutments (trans-mucosal part of the 2 stage implant) were replaced by either a new titanium abutment or a fluor-ethylene-propylene (FEP) coated abutment per subject. After 3 months of habitual oral hygiene, plaque samples were taken. Supragingival plaque was examined by means of differential phase-contrast microscopy, whereas for the subgingivial plaque additional analyses (DNA probes analysis, culturing) were performed. The subgingival samples were taken by paper-points and by scraping of the subgingival abutment surface. Differential phase-contrast microscopy showed a significant difference in plaque composition, especially when supragingival plaque was considered (P = 0.05). FEP coated abutments frequently harbored more coccoid microorganisms, whereas spirochetes or motile organisms were only detected around titanium abutments. Subgingivally, the number of colony forming units (CFU) in paper-points was comparable for both types of abutments. If the to-the-abutment-adhering plaque was considered, the number of CFU was 5 times higher on the titanium abutments than on the FEP coated abutments. However, this difference did not reach a statistical level of significance (P = 0.38). The DNA probe analysis of the subgingival plaque collected with paper-points showed a slightly higher frequency and concentration of perio-pathogens around the titanium abutments. However, the inter-substratum differences were smaller than the inter-subject differences. The latter seemed to be related to patient's dental status.(ABSTRACT TRUNCATED AT 250 WORDS)

Microbial adhesion to hydrocarbons (MATH) and microelectrophoresis were done in 10 mM potassium phosphate solutions to characterize the surfaces of thermophilic dairy streptococci, isolated from pasteurizers. Regardless of whether they were grown (in M17 broth) with lactose, sucrose, or glucose added, strains were relatively hydrophilic (showing low initial removal rates by hexadecane) and slightly negatively charged. A tendency exists for cells grown with sucrose added to be more hydrophilic than cells grown with glucose or lactose added. Also, the lowest isoelectric points, i.e., the pH values for which the zeta potentials are zero, were measured for strains with glucose added to the growth medium. The isoelectric points for the strains were all rather high, between pH 3 and 5, indicative of protein-rich surfaces, although X-ray photoelectron spectroscopy did not measure excessively large amounts of nitrogen on the cell surfaces. Both MATH and microelectrophoresis were done as a function of pH. Maxima in hydrophobicity were observed at certain pH values. Usually these pH values were in the range of the isoelectric points of the cells. Thus it appears that MATH measures an interplay of hydrophobicity and electrostatic interactions. MATH measures solely hydrophobicity only when electrostatic interactions are absent, i.e., close to the isoelectric points of the cells. Considering that these thermophilic streptococci are all rather hydrophilic, a possible pathway to prevent fouling in the pasteurization process might be to render the heat exchanger plates of the pasteurizer more hydrophobic.

The grouping and identification made by Fourier-transform infrared spectroscopy (FT-IR) of 40 oral streptococcal strains was compared with their known taxonomic positions. Grouping was obtained by cluster analysis on the spectral distances between the first derivative spectra of the strains. Spectra were divided into five spectral 'windows' and cluster analysis was either on either a combination of all five windows or on a selected window. The oral streptococci were divided into two main clusters, mutans streptococci and other streptococci. This division was based mainly on the spectral information contained in the window between 1300-900 cm-1, indicative of polysaccharide and phosphate-carrying compounds. In the grouping based on the entire spectrum, species clusters could be observed for Streptococcus crista, Strep. salivarius and Strep. rattus. A few strains were placed in wrong clusters because of intra-strain variance. It is concluded that the grouping of these oral streptococcal species was good and similar to the classical taxonomy and that FT-IR might develop into a new identification method for oral streptococci.

In nine patients with fixed prostheses supported by endosseous titanium implants, 2 titanium abutments (transmucosal part of the implant) were replaced by either an unused standard abutment or a roughened titanium abutment. After 3 months of habitual oral hygiene, plaque samples were taken for differential phase-contrast microscopy, DNA probe analysis, and culturing. Supragingivally, rough abutments harbored significantly fewer coccoid micro-organisms (64 vs. 81%), which is indicative of a more mature plaque. Subgingivally, the observations depended on the sampling procedure. For plaque collected with paper points, only minor qualitative and quantitative differences between both substrata could be registered. However, when the microbiota adhering to the abutment were considered, rough surfaces harbored 25 times more bacteria, with a slightly lower density of coccoid organisms. The presence and density of periodontal pathogens subgingivally were, however, more related to the patient's dental status than to the surface characteristics of the abutments. These results justify the search for optimal surface smoothness for all intra-oral and intra-sulcular hard surfaces for reduction of bacterial colonization and of periodontal pathogens.

Positive cooperativity is a mechanism proposed to account for the adhesion of bacteria to surfaces. In this paper, two methods that both claim to assess experimentally cooperative phenomena, viz. Scatchard analysis of adhesion data (using adhesion to vials) and analysis of the spatial arrangement of adhering cells (using a flow chamber), were compared and critically evaluated. Three oral strains were used and the substrata involved were glass (hydrophilic) and silicone-coated glass (hydrophobic) employed with or without a salivary coating. Scatchard analysis and near-neighbour analysis of adhering cells yield similar conclusions with regard to the mechanism of adhesion of the cells, provided that adhering cells are sufficiently immobilized under the experimental conditions. In the case of incomplete immobilization, near-neighbour collection results from sliding of adhering cells rather than from cooperative phenomena. Also, the agreement between the conclusions from both methods seems to be better, the more reversibly the cells adhere. Positive cooperativity can be absent or present on saliva-coated substrata with a distinct effect of the substratum hydrophobicity, despite the presence of an adsorbed film. This suggests that a different pellicle develops on a hydrophobic substratum than on a hydrophilic substratum. This is confirmed by our observation that the amino acid composition of salivary films is different on both types of substratum.

Silicone voice prostheses used for rehabilitation of speech after total laryngectomy are inserted in an non-sterile habitat. Deposits on explanted Groningen Button voice prostheses revealed a biofilm, due to heavy colonization of the silicone surface by bacteria and yeasts. Furthermore, it was demonstrated by scanning electron microscopy on sectioned explants that the silicone material was deteriorated by filamentous and vegetative yeast cells. The different explants showed a variety of sharp-edged, discrete yeast colonies. The yeasts grew just under the silicone surface and up to 700 microns into the silicone material. Finally, nine different types of defects in the silicone material created by the yeasts are described. This deterioration of the silicone by yeasts seems to be the main reason for the failure and the frequent replacement of the prostheses. The mechanisms of silicone deterioration are still hypothetical.

In the human body, cells contacting biomaterials surfaces are frequently exposed to pulsatile shear stresses, e.g. blood vessel prostheses. Most studies involving shear, however, try to achieve a steady, pulse-free shear stress in studying cell-biomaterial interactions. In this study, human fibroblasts adhering to glass were exposed to an applied 0.5 Hz square-wave pulsatile shear, created in a parallel plate flow chamber by a computer-driven pump. Cells were also exposed to the single lower and higher shear stresses making up the square wave in the presence or absence of pressure variations due to the peristaltic roller pump. Results indicate that cells exposed to the applied square-wave regime showed a detachment rate in between that of the single shear stresses making up the square wave. Furthermore, the presence of the pulsations gave rise to elongated cell shapes in the direction of flow and the formation of a more extensive filopodial network than in the absence of pulsations. This was also true for cells exposed to the high shear component in the presence of pressure variations. Cells exposed to the high shear component without any pressure variations, however, adapted spherical shapes after the onset of flow.

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.

Porphyromonas gingivalis, Prevotella intermedia, and Actinobacillus actinomycetemcomitans (A.a.) are Gram-negative bacteria which are implicated in various forms of periodontal disease. The Gram-positive Peptostreptococcus micros may also play an important role. For investigation of the possible adhesion and colonization mechanisms of these organisms, the charge properties of the outermost layers of bacterial cell surfaces were studied through the measurement of zeta potentials at various pH values. Eleven fresh clinical isolates, representing the four species, and one laboratory strain, P. gingivalis W83, were examined. Eleven of the 12 strains displayed heterogeneity with respect to pH-dependent zeta potentials. Within single cultures of each of these strains, two distinct populations of cells were found, one which was more negatively charged than the other. For the Gram-negative strains, the more negatively charged subpopulation was in the majority, while the P. micros strains appeared to be composed mainly of a less-negatively-charged subpopulation. Vesicles prepared from two strains displayed the same pH dependence and heterogeneity of zeta potentials as the parent cells. An A.a. strain which was passaged several times in fluid medium had lost its fimbriae and became homogeneous with respect to charge.

Seven clinical isolates of lactobacilli were found to be relatively hydrophobic with a mean water-contact angle of 66 +/- 15 degrees, and to be susceptible to 1% nonoxynol-9 and vancomycin. However, seven other strains were relatively hydrophilic with a mean water-contact angle of 32 +/- 13 degrees, and found to be resistant to 25% nonoxynol-9 and vancomycin. Thus, the surface properties of lactobacilli that influence susceptibility to antimicrobial agents may involve surface hydrophobicity. Possibly the penetration barrier posed by the cell surface towards these two nonionic antimicrobials is lower for hydrophobic cells than for hydrophilic cells.

In this paper, it is suggested that specificity and non-specificity in (oral) microbial adhesion are different expressions for the same phenomena. It is argued that the same basic, physicochemical forces are responsible for so-called 'non-specific' and 'specific' binding and that from a physico-chemical point of view the distinction between the two is an artificial one. Non-specific interactions arise from Van der Waals and electrostatic forces and hydrogen bonding, and originate from the entire cell. A specific bond consists of a combination of the same type of Van der Waals and electrostatic forces and hydrogen bonding, now originating from highly localized chemical groups, which together form a stereochemical combination. The absence or presence of specific receptor sites on microbial cell surfaces must therefore be reflected in the overall, non-specific surface properties of cells as well. This point is illustrated by showing that glucan-binding lectins on mutans streptococcal strains may determine the pH dependence of the zeta potentials of these cells. When studying microbial adhesion, a non-specific approach may be better suited to explain adhesion to inert substrata, whereas a specific approach may be preferred in case of adhesion to adsorbed protein films. Adhesion is, however, not as important in plaque formation in the human oral cavity as is retention, because low shear force periods, during which adhesion presumably occurs, are followed by high shear force periods, during which adhering cells must withstand these detachment forces. Evidence is provided that such detachment will be through cohesive failure in the pellicle mass, the properties of which are conditioned by the overall, non-specific substratum properties. Therefore, in vivo plaque formation may be more readily explained by a non-specific approach.

A parallel-plate flow chamber is developed in order to study cellular adhesion phenomena. An image analysis system is used to observe individual cells exposed to flow in situ and to determine area, perimeter, and shape of these cells as a function of time and shear stress. With this flow system the behavior of human fibroblasts spread on glass is studied when exposed to an increasing laminar flow. The flow system appears to be well-suited for following individual cells during detachment. After 75 to 90 min, at a shear stress of 350 dynes/cm2, more than 50% of the spread cells are detached from the surface. Cells with higher spreading areas stay longer at the glass surface. Cells round up before detaching. Sometimes the cell body is attached to the substratum through a thin filament during detachment. At the scanning electron microscopy level numerous filopodial extensions are observed. Cell material could only rarely be observed at the light or scanning electron microscopic level on the substratum once a cell was detached.

The aim of this study was to examine the hydrophobicities of 23 urogenital, dairy, poultry, and American Type Culture Collection isolates of lactobacilli and to determine the effect on hydrophobicity of serially passaging the strains in liquid medium. To this end, strains were grown after isolation and identification and then serially passaged up to 20 times. Hydrophobicity was assessed through contact angle measurements on lawns of cells by using water, formamide, methylene iodide, 1-bromonaphthalene, and hexadecane as wetting agents and through measurement of their partitioning in a hexadecane-water system. The hydrophobicities of these strains varied widely, with Lactobacillus casei strains being predominantly hydrophilic and L. acidophilus strains being mostly hydrophobic. For some isolates, serial passaging was accompanied by a clear loss of hydrophobic surface properties, whereas for other strains, cultures became heterogeneous in that some cells had already lost their hydrophobic surface properties while others were still hydrophobic. Adhesion of this collection of lactobacilli to hexadecane droplets in microbial adhesion to hexadecane (MATH) tests was driven by their aversion to water rather than by their affinity for hexadecane, as concluded from the fact that hexadecane contact angles were zero for all strains. Furthermore, adhesion of the lactobacilli to hexadecane in MATH tests occurred only when the water contact angle on the cells was above 60 degrees.

The surfaces of nine clinical isolates of Porphyromonas gingivalis, Prevotella intermedia, Actinobacillus actinomycetemcomitans, and Peptostreptococcus micros and that of laboratory strain P. gingivalis W83 were studied by using contact angle measurements, X-ray photoelectron spectroscopy, infrared spectroscopy, microelectrophoresis of whole cells, and transmission electron microscopy of whole and sectioned cells. P. intermedia strains were hydrophilic, as judged from their small water contact angles, and had highly negative zeta potentials, consistent with the presence of a prominent ruthenium red (RR)-staining layer and fibrillar appendages which are probably partly carbohydrate. The two clinical isolates of P. gingivalis were also hydrophilic and highly negatively charged despite the presence of prominent fibrils, which usually yield less negative zeta potentials. This finding suggests that the RR-staining layer dominates the suspension characteristics of P. gingivalis and P. intermedia strains. P. gingivalis W83 had no demonstrable fibrils and a morphologically distinct RR-staining layer, and it was more hydrophobic than the two clinical isolates of P. gingivalis. P. micros isolates were hydrophobic and much less negatively charged than the other species. The A. actinomycetemcomitans strains displayed long, prominent fibrils and a very thin RR-staining layer, which resulted in high hydrophobicity but distinctly different zeta potentials for the two. Physicochemical data on microbial cell surfaces usually have clear and predictable relationships with each other. For the strains in this study that did not follow these relationships, their aberrant behavior could be explained as due to a masking effect caused by specific surface architecture. We conclude that this combined analysis provides a detailed image of subgingival bacterial surface architecture.

In order to determine the response of fixed and nonfixed cells adherent to a solid substratum to shear stress, human fibroblasts were allowed to adhere and spread on either hydrophilic glass or hydrophobic Fluoroethylene-propylene (FEP-Teflon) and fixed with glutaraldehyde. Then, the cells were exposed to an incrementally loaded shear stress in a parallel plate flow chamber up to shear stresses of about 500 dynes/cm2, followed by exposure to a liquid-air interface passage. The cellular detachment was compared with the one of nonfixed cells. In case of fixed cells, 50% of the adhering cells detached from FEP-Teflon at a shear stress of 350 dynes/cm2, whereas 50% of the adhering, nonfixed cells detached already at a shear stress of 20 dynes/cm2. No fixed cells detached from glass for shear stresses up to at least 500 dynes/cm2. More than 50% of the nonfixed cells were detached from glass at a shear stress of 350 dynes/cm2. Furthermore, the shape and morphology of fixed cells did not change during the incrementally loaded flow, in contrast to the ones of nonfixed cells, which clearly rounded up prior to detachment.

Deposition and adhesion to glass with and without a salivary coating in a parallel-plate flow chamber were studied with four strains of mutans streptococci. Stationary-state adhesion of the strains to uncoated glass ranged from 0.3 x 10(6) cm-2 (Streptococcus rattus HG218) to 12.7 x 10(6) cm-2 (Streptococcus sobrinus HG1025) and generally decreased after saliva coating of the glass. The poor adhesion found for S. rattus HG218 to both uncoated and saliva-coated glass could be due to its relatively high negative surface-charge. Deposition efficiencies of all strains were greater than or equal to 1 for uncoated glass and decreased greatly after saliva coating of the glass. Possibly, adhesion to a saliva coating is less efficient and more time-consuming than that to uncoated glass, because stereochemical groups in the pellicle and on the cell surfaces may have to re-arrange before an effective interaction can occur. Desorption rates, measured 1000 s and 5000 s after the start of an experiment, decreased by a factor of ten upon a five-fold increase in contact time, indicative of a two-phase adhesion process. Of the four strains studied, only Streptococcus cricetus HG737 showed a minor positive cooperativity on saliva-coated glass, possibly mediated by surface appendages observed by transmission electron microscopy on negatively-stained cells. Retention of adhering bacteria was strain-dependent on uncoated glass, but was identical for all strains on saliva-coated glass, which suggests that the structure and composition of the pellicle may be more important with respect to the retention of adhering cells than the cell-surface properties themselves.

Elemental surface concentration ratios N/C,O/C, and P/C of fibroblasts, HELA epithelial cells, and smooth muscle cells, prior to and after washing in the absence or presence of serum proteins, were determined by X-ray photoelectron spectroscopy. Cell surfaces appeared to adsorb hardly any serum proteins, and the relatively high P/C, as compared to N/C and O/C, elemental surface concentration ratio indicated that the cell surfaces consisted mainly of the phospholipid bilayer, with little or no proteins present. The lack of adsorption of serum proteins to the cell surfaces seems at odds with the common notion that cells require adhesive proteins in order to adhere and spread. However, the adsorption behavior of cellularly produced proteins may be completely different, particularly since they seem to be able to displace adsorbed serum proteins from biomaterials surfaces. Interestingly, only HELA epithelial cells (a tumor cell line) appeared to adsorb a very small amount of proteins.

Eight Escherichia coli strains were characterized by determining their adhesion to xylene, surface free energy, zeta potential, relative surface charge, and their chemical composition. The latter was done by applying X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). No relationship between the adhesion to xylene and the water contact angles of these strains was found. Three strains had significantly lower surface free energies than the other strains. Surface free energies were either obtained from polar and dispersion parts or from Lifshitz-van der Waals and acid/base parts of the surface free energy. A correlation (r = 0.97) between the polar parts and the electron-donor contributions to the acid/base part of the surface free energy was found. The zeta potentials of all strains, measured as a function of pH (2-11), were negative. Depending on the zeta potential as a function of pH, three groups were recognized among the strains tested. A relationship (r = 0.84) was found between the acid/base component of the surface free energy and the zeta potential measured at pH = 7.4. There was no correlation between results of XPS and IR studies. Data from the literature of XPS and IR studies of the gram-positive staphylococci and streptococci were compared with data from the gram-negative E. coli used in this study. It appeared that in these three groups of bacteria, the polysaccharide content detected by IR corresponded well with the oxygen-to-carbon ratio detected by XPS.

X-ray photoelectron spectroscopy (XPS) on microbial cell surfaces requires freeze-drying of cells, and as a result, the cell surface appendages flatten out on the cell surface and form a collapsed fibrillar mass. At present, it is unclear how the density, length and composition of these fibrils influence the elemental surface composition as probed by XPS. The sampling depth of XPS can be varied by changing the electron take-off angle. In this article, we made a depth profiling of the collapsed fibrillar mass of Streptococcus salivarius HB and fibril-deficient mutants by angle-dependent XPS. Methylamine tungstate negative staining and ruthenium red staining followed by sectioning revealed distinct classes of fibrils with various lengths on each of the strains. Interpretation of the angle dependence of the oxygen/carbon (O/C) and phosphorus/carbon (P/C) surface concentration ratios of these strains was difficult. However, the angle dependence of the nitrogen/carbon (N/C) surface concentration ratio could be fully interpreted: N/C did not vary with sampling depth on a bald strain, S. salivarius HBC12 and on S. salivarius HB7, a strain with a dense array of fibrils of uniform length. N/C decreased with sampling depth in case of a sparsely fibrillated strain, S. salivarius HBV51 and eventually reached the value observed for the bald strain, HBC12. A high N/C at small sampling depth was observed for S. salivarius HB with protruding, protein rich fibrils. We conclude that elemental depth profiling of microbial cell surfaces by XPS can be interpreted to coincide with structural and biochemical information on the cell surface as obtained by electron microscopy and can therefore be considered as a useful technique to study structural features of cell surfaces in combination with electron microscopy.

To determine the strength of adhesion and the detachment mechanisms of fibroblasts from substrata with different wettability, the behaviour of adhered cells was studied in a parallel-plate flow chamber during exposure to shear. Adhered cells were observed in situ, i.e. in the flow chamber, by phase-contrast microscope and images were analysed semiautomatically. Detachment was found to be dependent both on shear stress and time, although a critical shear stress can be found below which no detachment occurs. On all substrata, cells round up before detachment and are approximately spherical immediately before detachment. The strength of adhesion calculated ranged from 0.6-3.5 x 10(-10) N per cell on FEP-Teflon (the least wettable material included) to 9.4 x 10(-9) N per cell for glass (the most wettable). Ease of detachment seemed to decrease with increasing wettability. However, cells reacted more strongly with tissue culture polystyrene (TCPS) than expected on the basis of its wettability, probably due to surface chemistry.

Mutans streptococci comprise a group of seven closely related, yet distinct species. The distinction between the four species used in this study, namely Streptococcus sobrinus, Streptococcus cricetus, Streptococcus rattus, and Streptococcus mutans, has been made only recently on the basis of DNA homologies. In order to determine if there is a difference in the physicochemical surface properties of these species, strains were characterized by contact angles, zeta potentials and isoelectric points (IEP), elemental surface compositions by X-ray photoelectron spectroscopy, and molecular moieties by infrared spectroscopy. Contact angles, particularly when measured with water, can be considered a measure of cell surface hydrophobicity; zeta potentials reflect the charge of the outermost cell surface; X-ray photoelectron spectroscopy yields the relative abundance of carbon, oxygen, nitrogen, and phosphorus over the outer 5 nm of the bacterial cell surface; infrared spectroscopy enables a molecular characterization in terms of proteins, phosphates, and polysaccharides. All four species were homogeneous with regard to their physicochemical surface properties. However, the S. rattus species were clearly different from the others on the basis of the low water contact angle (21 +/- 2 vs. 26-31 degrees), highly negative zeta potential and lack of IEP, and high oxygen/carbon (0.50 +/- 0.02 vs. 0.41-0.43) and phosphorus/carbon (0.016 +/- 0.001 vs. 0.006-0.008) surface concentration ratios. Amongst the other differences observed, each species had a characteristic pH dependence of their zeta potential measured in phosphate buffer, yielding an IEP of 1.7, 2.1, and 2.5 for S. cricetus, S. sobrinus, and S. mutans, respectively. However, a cluster analysis on the zeta potential data showed only an isolated cluster for the S. rattus species. Thus it is likely that the higher cariogenicity of S. sobrinus with respect to S. cricetus and S. mutans is, in addition to a higher acidogenicity, due to the smaller negative surface charge, giving an increased adhesion to negatively charged tooth surfaces. S. rattus is expected to be the least adherent strain in the oral cavity as it carries a relatively high negative surface charge.

Neither proteins nor bacteria adsorb or adhere homogeneously to a substratum surface. The final two-dimensional spatial arrangement depends on a complicated interplay between protein-protein (bacterium-bacterium) and protein (bacterium)-substratum interactions and the prevailing hydrodynamic conditions. In this paper, results are presented of two separate experiments in which bovine serum albumin (BSA) was adsorbed to, or Streptococcus sanguis 12 was deposited on substrata with different wettabilities in a search for analogies in the two-dimensional spatial arrangement of the absorbed proteins and adhering bacteria. The spatial arrangement of adsorbed BSA, visualized by transmission electron microscopy on replicas of the surface, was island-like on substrata with a low wettability and well distributed on substrata with a high wettability. The spatial arrangement of adhering S. sanguis 12 was observed directly by light microscopy during the experiment and showed a relatively large collection of near-neighbour sites on the low wettability substrata compared with the high wettability substrata. Thus, it seems that the occurrence of island-like structures in protein adsorption is concurrent with a large collection of near-neighbour sites in bacterial adhesion. As a possible explanation for the above analogy, it is suggested that proteins or bacteria are insufficiently immobilized on low wettability substrata owing to weak interaction forces, and they can move over the substratum surface to yield the two-dimensional spatial arrangements observed.

The adsorption of active agents from six commercially available mouthrinses to ground and polished enamel, with and without adsorbed salivary constituents, was monitored by contact angle measurements and X-ray Photoelectron Spectroscopy (XPS). Human enamel samples were treated with mouthrinses containing chlorhexidine (Peridex), stannous fluoride/amine fluoride (Meridol), thymol/benzoic acid (Listerine), sanguinarine (Veadent), sodium fluoride (Prodent), or cetylpyridinium chloride (Merocet). XPS indicated a sizeable adsorption of both active and non-active components for all products. After treatment, all enamel surface free energies increased except for the stannous fluoride/amine fluoride containing mouthrinse. It is suggested that non-active components in the products cause an increase in surface free energy. Despite this thermodynamically unfavorable increase in surface free energy, all rinses have plaque reducing effects, indicating that this unfavorable surface characteristic is overruled by the antibacterial properties of the components. Replacement of non-active components by less adsorbing surfactants could increase the efficiency of the products tested.

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.

This study evaluated physicochemical properties of eight commercially available mouthrinses, namely surface tension, in vivo enamel contact angle, viscosity, penetration coefficient, acidity and buffer capacity. The penetration coefficient, determined by the surface tension, contact angle and viscosity, is a measure of the ability of a liquid to penetrate into a capillary space, such as interproximal regions, gingival pockets and pores. The acidity is often determined by a compromise of the requirements for taste, enamel remineralization and stability of the solution. Among the eight mouthrinses evaluated, the physicochemical properties differed greatly, in particular, the penetration coefficient which varied by a factor of 1.8 over the products tested. Surprisingly several of the products tested were found to be extremely acidic.

The spatial arrangement of two strains of oral bacteria adhering on glass was studied in order to investigate cooperative effects in their adhesion mechanisms. Streptococcus salivarius HB was a strain which possessed several classes of fibrillar surface appendages, whereas on the cell surface of S. mutants NS no surface appendages could be identified. The bacteria were deposited from a flowing suspension with various buffer concentrations on the bottom glass plate of a parallel plate flow cell and were observed directly with a video camera mounted on a phase contrast microscope. The positions of all adhering bacteria were determined by means of automated real time image analysis and subsequently employed for calculating radial and angular pair distribution functions. Pair distribution functions indicate the average relative number density of bacteria around one deposited bacterium as a function of the radial distance or the angular orientation relative to the flow direction. From the calculated pair distribution functions of both bacterial strains it was concluded that cooperative effects contributed to the adhesion of S. salivarius HB, but not to adhesion of S. mutants NS. It was suggested that these cooperative effects originate from the surface appendages of S. salivarius HB.

To determine the influence of cetylpyridinium chloride (CPC) adsorption on the wettability and elemental surface composition of human enamel, with and without adsorbed salivary constituents, surface-free energies and elemental compositions were determined. The surface-free energies were estimated from contact angle measurements; whereas the elemental compositions were determined by X-ray photoelectron spectroscopy. Surface-free energies of ground and polished enamel (88 +/- 8 mJ.m-2 and saliva-coated enamel (103 +/- 4) became similar (109-112) upon adsorption of CPC. Also, the N/C concentration ratios of the ground and polished enamel surface (0.06) and saliva-coated enamel (0.21) become equal upon CPC adsorption. The N/C concentration ratio after CPC adsorption (N/C = 0.04) corresponds with the value expected on basis of the molecular structure of CPC. The strongest evidence for adsorption of CPC to both ground and polished enamel and saliva-coated enamel is presented by the double nitrogen N1s peak. This double nitrogen1s peak is not observed for ground and polished enamel nor for enamel with a salivary coating on top of adsorbed CPC, which indicates that adsorbed CPC can be completely screened by salivary proteins. This study demonstrates that CPC has a definite capacity to adsorb both on ground and polished enamel as well as on pellicle-coated enamel.

The surface properties of five freshly isolated clinical strains of Actinobacillus actinomycetemcomitans and a non-sticky, non-cohesive colonial variant were characterized. On growth in serum-containing and serum-free media, the primary isolates had a high surface free energy, corresponding with the low hydrophobicity observed, using as assay adsorption to hexadecane. The dispersion component of the surface free energy was significantly lower upon growth in serum-free medium. In the electron microscope the cells appeared covered with vesicles. In sharp contrast, the colonial variant had a very low surface free energy but still showed a low hydrophobicity in the hexadecane assay. Expression of the surface free energy characteristics in serum-grown cultures appeared strongly dependent on cell treatment, suggesting a significant influence of an adsorbed proteinaceous layer. The cells of the variant strain generally carried fewer surface vesicles. No major difference was observed in the outer membrane protein composition between parent and variant strain.

Most Streptococcus salivarius (K+) cells contain two protein antigens with different adhesive functions. The subcellular distribution and some structural properties of purified proteins were studied. Antigen B (AgB), a protein involved in interbacterial coaggregation with gram-negative bacteria, was present in the cell wall fraction only of the wild-type strain and was absent from the cells of a nonadhesive mutant. Antigen C (AgC), a glycoprotein involved in host-associated adhesive functions, was predominantly associated with the cell wall of the wild-type strain (AgCw), but accumulated in high amounts in the cytoplasmic fraction (AgCin) of mutants lacking the wall-associated form. AgB, AgCw, and AgCin had molecular weights of 380,000, 250,000 to 320,000, and 488,000, respectively, upon gel electrophoresis under nondenaturing conditions. In the presence of sodium dodecyl sulfate and beta-mercaptoethanol the molecular weights were only slightly lower, suggesting that the free, isolated molecules exist as monomers under native conditions. AgCin readily stained with periodate-Schiff reagent, indicating a significant content of carbohydrate, similar to AgCw. Circular dichroism spectra showed that about 45% of the amino acids of AgCw were involved in alpha-helical coiled structures. AgB had a significantly lower proportion of ordered coiled structure. Electron microscopic observations of low-angle-shadowed preparations of purified antigens showed that they were flexible, thin rods with thickened or globular ends. Measurements corrected for shadow thickness showed lengths of 184 nm (AgB), 112 nm (AgCin), and 87 nm (AgCw). Treatment of AgCw with protease destroyed the fibrillar core, but seemed not to affect the globular ends. Comparison of the results with the localization of the antigens in wild-type and specific mutant strains suggested that each antigen molecule may represent a single, characteristic surface fibril with a specific adhesive capacity.

An experimental technique is described to determine contact angles on bacterial layers deposited on cellulose triacetate filters. Measurements with water, water-n-propanol mixtures, and alpha-bromonaphthalene were employed to calculate surface free energies of various oral bacteria. Differences of 30 to 40 erg cm-2 were obtained for four different bacterial species isolated from the human oral cavity, if the concept of dispersion and polar surface free energies is applied. The free energies obtained were used to calculate interfacial free energies of adhesion of these bacteria from saliva onto tooth surfaces. Bacterial adhesion is energetically unfavorable, if the enamel surface free energy is less than 50 erg cm-2.

In vitro adsorption of chlorhexidine from a commercially available chlorhexidine-containing (0.12%) mouthrinse (Peridex) on both ground and polished and on saliva-coated enamel was studied by X-ray photoelectron spectroscopy and contact angle measurements. Furthermore, adsorption of salivary constituents was studied on chlorhexidine-treated enamel. Changes in the elemental surface composition obtained by X-ray photoelectron spectroscopy clearly demonstrated adsorption of chlorhexidine from the mouthrinse as indicated by increased N and C signals which were in all cases accompanied by a higher enamel surface free energy, estimated from the contact angle data. In addition, it was found that salivary constituents adsorb less to chlorhexidine-treated enamel than to ground and polished enamel and, moreover, that adsorbed salivary constituents were desorbed by chlorhexidine. In vivo, the effect of a 3-week use of chlorhexidine was compared with the use of a placebo and habitual oral hygiene of 10 volunteers by means of clinical contact angle measurements. Also in vivo adsorption of chlorhexidine yielded elevated surface free energies with respect to habitual oral hygiene or a placebo. Thus in vivo, the well-known favourable effects of the bactericidal properties of chlorhexidine completely overrule the unfavourable effects of high enamel surface free energies.

Cell surfaces of three nonencapsulated and three encapsulated coagulase-negative staphylococci were characterized by their surface free energies, zeta potentials, and elemental and molecular compositions. Surface free energies were calculated from contact angle measurements with various liquids. All six strains showed a high surface free energy (103 to 126 mJ.m-2), estimated from the concept of polar and dispersion components. However, the hydrogen-donating surface free energy parameter was zero for all nonencapsulated strains. The zeta potential profile measured as a function of pH in phosphate-buffered saline for the nonencapsulated strains was completely different from that of the encapsulated strains. X-ray photoelectron spectroscopy was used to determine the elements (O, C, N, P, and K) in the outer 2 to 5 nm of the freeze-dried cell surface and showed that the hydrophilic character of the staphylococci was related to oxygen (O/C ratio, approximately 0.52)- and phosphorus (P/C ratio, approximately 0.03)-containing groups. Both the elemental and molecular characterizations (done by infrared spectroscopy) pointed to the presence of polysaccharides and polypeptides on the cell surface of the nonencapsulated and encapsulated strains.

The adhesion of Streptococcus mitis to solid substrata from phosphate suspensions with various ionic strengths was studied and compared with the adhesion of polystyrene particles. At all ionic strengths, the interfacial free energy of adhesion governed the relative number of bacteria or polystyrene particles adhering at equilibrium, except that in a low-ionic-strength buffer, adhesion occurred less frequently because of increased electrostatic repulsion. Large differences between bacterial and polystyrene particle adhesion were observed, as indicated by the ratio of bacteria to polystyrene particles adhering, which decreased from 30 to 4 with a change from low to high ionic strength.

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 (O, 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.

Adhesion of Candida albicans to the acrylic fitting surface of dentures can lead to the development of denture induced stomatitis and is suggested to be preceeded by the adhesion of indegeneous oral bacteria. Bacterial adhesion can be considered as a result of attractive van der Waals and repulsive electrostatic forces. In this paper we investigate the role of electrostatic interactions in the adhesion of oral streptococci to polymethylmethacrylate (PMMA), the most commonly employed denture-base material. Zeta potentials of the bacterial strains as well as of PMMA fillings were reduced by increasing the ionic strength in the buffer suspension, causing an elevated number of adhering S. mitis, S. sanguis and S. mutans. As streptococcal adhesion is suggested to be a prerequisite for the subsequent adhesion of Candida albicans, the use of more negatively charged denture-base materials can be recommended in order to prevent streptococcal adhesion and therewith adhesion of candidae, and the occurrence of denture-induced stomatitis.