Influence of Pretreatment and Experimental Conditions on Electrophoretic Mobility and Hydrophobicity of Cryptosporidium parvum Oocysts

Surface properties of Cryptosporidium parvum oocysts were investigated by using electrophoretic mobility and hydrophobicity measurements. Oocysts purified from calf feces by several sucrose flotation steps and deionized water (DI) washes (DIS method) had an electrophoretic mobility (neutral surface charge) near 0.0 m² V⁻¹ s⁻¹ over a pH range of 2 to 10. The mean electrophoretic mobility of oocysts stored in DI containing a mixture of antibiotics had a lower standard deviation (ς = 0.36) than that of oocysts stored in DI without antibiotics (ς = 0.53); their electrophoretic mobility remained unchanged up to 121 days after collection. The electrophoretic mobility of oocysts purified on a cold Percoll-sucrose gradient after the feces was defatted with ethyl acetate (EAPS method) varied linearly with pH from 0.0 m² V⁻¹ s⁻¹ at pH 2.4 to −3.2 × 10⁻⁸ m² V⁻¹ s⁻¹ at pH 10 (ς = 0.52), thus displaying the negative surface charge at neutral pH observed by other researchers. The hydrophobicity of oocysts and two types of polystyrene beads was measured as a function of ionic strength by adhesion to polystyrene. Oocysts were purified by the DIS method. The ionic strength of the suspending solution was varied from 0 to 95 mmol liter⁻¹. Two-week-old oocysts exhibited strong adhesion (~85%) at ionic strengths of 0 to 10 mmol liter⁻¹ and moderate adhesion (~20%) at ionic strengths of 20 to 95 mmol liter⁻¹. Two-month-old oocysts exhibited high adhesion (~60 to 80%) at all ionic strengths. These results show that adhesion properties governed by the electrophoretic mobility of purified C. parvum oocysts can be altered by the method of purification and that hydrophobicity can change as oocysts age.     

Surface Physicochemistry and Ionic Strength Affects eDNA’s Role in Bacterial Adhesion to Abiotic Surfaces

Extracellular DNA (eDNA) is an important structural component of biofilms formed by many bacteria, but few reports have focused on its role in initial cell adhesion. The aim of this study was to investigate the role of eDNA in bacterial adhesion to abiotic surfaces, and determine to which extent eDNA-mediated adhesion depends on the physicochemical properties of the surface and surrounding liquid. We investigated eDNA alteration of cell surface hydrophobicity and zeta potential, and subsequently quantified the effect of eDNA on the adhesion of Staphylococcus xylosus to glass surfaces functionalised with different chemistries resulting in variable hydrophobicity and charge. Cell adhesion experiments were carried out at three different ionic strengths. Removal of eDNA from S. xylosus cells by DNase treatment did not alter the zeta potential, but rendered the cells more hydrophilic. DNase treatment impaired adhesion of cells to glass surfaces, but the adhesive properties of S. xylosus were regained within 30 minutes if DNase was not continuously present, implying a continuous release of eDNA in the culture. Removal of eDNA lowered the adhesion of S. xylosus to all surfaces chemistries tested, but not at all ionic strengths. No effect was seen on glass surfaces and carboxyl-functionalised surfaces at high ionic strength, and a reverse effect occurred on amine-functionalised surfaces at low ionic strength. However, eDNA promoted adhesion of cells to hydrophobic surfaces irrespective of the ionic strength. The adhesive properties of eDNA in mediating initial adhesion of S. xylosus is thus highly versatile, but also dependent on the physicochemical properties of the surface and ionic strength of the surrounding medium.     

The interaction between saliva and Actinobacillus actinomycetemcomitans influenced by the Zeta potential

The adhesion of Actinobacillus actinomycetemcomitans is a virulence factor in the aetiology of periodontitis and is determined by physico-chemical properties, e.g. surface charge and hydrophobicity, of the bacterial cell surface. Although oral surfaces are constantly coated with saliva, few studies have dealt with the binding of A. actinomycetemcomitans with saliva. In this report, the charge properties of A. actinomycetemcomitans have been studied through measurement of the zeta potential and the saliva-bacteria interaction investigated at different pH-values.At physiological conditions the zeta potential was negative, varying from -11 to -26 mV, for two laboratory and two fresh isolates of A. actinomycetemcomitans. Under these conditions, binding of the low-molecular-weight salivary mucin, lactoferrin, and S-IgA was confirmed using salivary samples and purified salivary fractions in liquid-phase and in ELISA. The iso-electric points of the laboratory and fresh clinical isolates of A. actinomycetemcomitans were determined at pH 4.6 and 3.8, respectively. At pH below the iso-electric point, giving positive values of the zeta potential, additional salivary protein species bound to A. actinomycetemcomitans, including the high-molecular-weight salivary mucin (MG1) and agglutinin. Binding of the low-molecular-weight salivary mucin (MG2), lactoferrin, and S-IgA, was hardly affected by this change in zeta potential. A salivary coating formed on the bacterium at pH 7 reduced the zeta potential of the laboratory strain Y4 greatly and an iso-electric point for the bacterium could not be determined. Overall, the study suggests that upon changes in environmental pH additional salivary attachment sites on the micro-organism are exposed.     

Interaction forces drive the environmental transmission of pathogenic protozoa

The protozoan parasites Giardia duodenalis, Cryptosporidium spp., and Toxoplasma gondii are pathogens that are resistant to a number of environmental factors and pose significant risks to public health worldwide. Their environmental transmission is closely governed by the physicochemical properties of their cysts (Giardia) and oocysts (Cryptosporidium and Toxoplasma), allowing their transport, retention, and survival for months in water, soil, vegetables, and mollusks, which are the main reservoirs for human infection. Importantly, the cyst/oocyst wall plays a key role in that regard by exhibiting a complex polymeric coverage that determines the charge and hydrophobic characteristics of parasites' surfaces. Interaction forces between parasites and other environmental particles may be, in a first approximation, evaluated following the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of colloidal stability. However, due to the molecular topography and nano- to microstructure of the cyst/oocyst surface, non-DVLO hydrophobic forces together with additional steric attractive and/or repulsive forces may play a pivotal role in controlling the parasite behavior when the organism is subjected to various external conditions. Here, we review several parameters that enhance or hinder the adhesion of parasites to other particles and surfaces and address the role of fast-emerging techniques for mapping the cyst/oocyst surface, e.g., by measuring its topology and the generated interaction forces at the nano- to microscale. We discuss why characterizing these interactions could be a crucial step for managing the environmental matrices at risk of microbial pollution.     

Adhesion of Chlorella vulgaris to solid surfaces, as mediated by physicochemical interactions

Although adhesion of bacteria and yeast have been extensively studied by a wide range of experimental and theoretical approaches, significantly less attention has been focused on microalgae adhesion to solid materials. This work is focused on physicochemical aspects of microalgae adhesion. The results are based on experimental characterization of surface properties of both microalgae and solids by contact angle and zeta potential measurements. These data are used in modeling the surface interactions (thermodynamic and colloidal models) resulting in quantitative prediction of the interaction intensities. Finally, the model predictions are compared with experimental adhesion tests of microalgae onto model solids in order to identify the physicochemical forces governing the microalgae–solid interaction. The model solids were prepared in order to cover a wide range of properties (hydrophobicity and surface charge). The results revealed that, in low ionic strength environment, the adhesion was influenced mostly by electrostatic attraction/repulsion between surfaces, while with increasing ionic strength grew the importance of apolar (hydrophobic) interactions. The impact of solid surface properties on the degree of colonization by microlagae was statistically more significant than the influence of medium composition on cell surface of Chlorella vulgaris.     

Efficient in vivo gene delivery by the negatively charged complexes of cationic liposomes and plasmid DNA

We examined changes in zeta potential (the surface charge density, zeta) of the complexes of liposome (nmol)/DNA (microg) (L/D) formed in water at three different ratios (L/D=1, 10 and 20) by changing the ionic strength or pH to find an optimum formulation for in vivo gene delivery. At high DNA concentrations, zeta of the complexes formed in water at L/D=10 was significantly lowered by adding NaCl (zeta=+8.44+/-3.1 to -27.6+/-3.5 mV) or increasing pH from 5 (zeta=+15.3+/-1.0) to 9 (zeta=-22.5+/-2.5 mV). However, the positively charged complexes formed at L/D=20 (zeta=+6.2+/-3.5 mV) became negative as NaCl was added at alkaline pH as observed in medium (zeta=-19.7+/-9.9 mV). Thus, the complexes formed in water under the optimum condition were stable and largely negatively charged at L/D=1 (zeta=-58.1+/-3.9 mV), unstable and slightly positively charged at L/D=10 (zeta=+8.44+/-3.7 mV), and unstable and largely positively charged at L/D=20 (zeta=+24.3+/-3.6 mV). The negatively charged complexes efficiently delivered DNA into both solid and ascitic tumor cells. However, the positively charged complexes were very poor in delivering DNA into solid tumors, yet were efficient in delivering DNA into ascitic tumors grown in the peritoneum regardless of complex size. This slightly lower gene transfer efficiency of the negatively charged complexes can be as efficient as the positively charged ones when an injection is repeated (at least two injections), which is the most common case for therapy regimes. The results indicate that optimum in vivo lipofection may depend on the site of tumor growth.     

Surface Properties of Bacteria from Different Wastewater Treatment Plants

The surface properties of the individual members of degradative biocommunities isolated from different laboratory and natural populations were characterized. The bacterial strains isolated from a given origin and degrading a given substrate varied with respect to their hydrophobic and electrostatic properties (e.g. contact angle, adsorption to hexadecane, isoelectric point, adsorption of anionic orcationic dyes). However, despite their specific surface characteristics, in most cases the net charge properties of different bacterial strains (characterized by the zeta potential profiles of the bacteria in relation to the pH) were found to be related to the substrate the bacteria were able to degrade as well as to the consortium the bacteria were isolated from. For one group of specialized bacteria, only oneor at most two characteristic zeta potential profiles were measured. Compared to the differences between different strains, the zeta potential profiles of individual strains were only slightly affected by either growth state or changes in the actual nutrient composition. Even if isolated strains were cultivated in standard nutrient broth for several months, only slight differences in the zeta potential profiles were measured. Only the isoelectric focusing experiments indicated thatcultivation in a complex medium favoured a progressively decreased uniformity of surface charge properties. Thus, measurement of zeta potential profiles under standardized conditions may be a useful means to compare the surface structures of bacteria from different origins.     

Specific and non-specific interactions in bacterial adhesion to solid substrata

Abstract Based on a literature review, a hypothesis is forwarded on the mechanism of initial bacterial adhesion to solid substrata, which accounts both for the role of specific microscopic surface components as well as for the role of non-specific macroscopic surface properties (surface free energy, zeta potential or hydrophobicity). Three distinct regions in the adhesion process are suggested in which at large and intermediate separation distances adhesion is mediated by the macroscopic surface properties as surface free energy and surface charge, respectively. At small separation distances specific short-range interactions can occur, leading to a strong and irreversible bonding, provided the water film present in between the interaction surfaces can be removed. A major role of hydrophobic groups, supposed to be associated with bacterial surface appendages is suggested to be its dehydrating capacity, enabling the removal of the vicinal water film yielding small areas of direct contact between protruberant parts of the cell surface and the substratum.     

Dependence of the initial adhesion of biofilm forming Pseudomonas putida mt2 on physico-chemical material properties

Bacterial adhesion is strongly dependent on the physico-chemical properties of materials and plays a fundamental role in the development of a growing biofilm. Selected materials were characterized with respect to their physico-chemical surface properties. The different materials, glass and several polymer foils, showed a stepwise range of surface tensions (γ(s)) between 10.3 and 44.7 mN m(-1). Measured zeta potential values were in the range between -74.8 and -28.3 mV. The initial bacterial adhesion parameter q(max) was found to vary between 6.6 × 10(6) and 28.1 × 10(6) cm(-2). By correlation of the initial adhesions kinetic parameters with the surface tension data, the optimal conditions for the immobilization of Pseudomonas putida mt2 were found to be at a surface tension of 24.7 mN m(-1). Both higher and lower surface tensions lead to a smaller number of adherent cells per unit surface area. Higher energy surfaces, commonly termed hydrophilic, could constrain bacterial adhesion because of their more highly ordered water structure (exclusion zone) close to the surface. At low energy surfaces, commonly referred to as hydrophobic, cell adhesion is inhibited due to a thin, less dense zone (depletion layer or clathrate structure) close to the surface. Correlation of q (max) with zeta potential results in a linear relationship. Since P. putida carries weak negative charges, a measurable repulsive effect can be assumed on negative surfaces.     

Altered sodium and gating current kinetics in frog skeletal muscle caused by low external pH

The effect of low pH on the kinetics of Na channel ionic and gating currents was studied in frog skeletal muscle fibers. Lowering external pH from 7.4 to 5.0 slows the time course of Na current consistent with about a +25-mV shift in the voltage dependence of activation and inactivation time constants. Similar shifts in voltage dependence adequately describe the effects of low pH on the tail current time constant (+23.3 mV) and the gating charge vs. voltage relationship (+22.1 mV). A significantly smaller shift of +13.3 mV described the effect of pH 5.0 solution on the voltage dependence of steady state inactivation. Changes in the time course of gating current at low pH were complex and could not be described as a shift in voltage dependence. tau g, the time constant that describes the time course of the major component of gating charge movement, was slowed in pH 5.0 solution by a factor of approximately 3.5 for potentials from -60 to +45 mV. We conclude that the effects of low pH on Na channel gating cannot be attributed simply to a change in surface potential. Therefore, although it may be appropriate to describe the effect of low pH on some Na channel kinetic properties as a "shift" in voltage dependence, it is not appropriate to interpret such shifts as a measure of changes in surface potential. The maximum gating charge elicited from a holding potential of -150 mV was little affected by low pH.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of cell surface damage on surface properties and adhesion of Pseudomonas aeruginosa

Bacterial cell surfaces play a crucial role in their adhesion to surfaces. In the present study, physico-chemical cell surface properties of Pseudomonas aeruginosa, isolated from a case of contact lens associated keratitis, are determined for mid-exponential and early stationary phase cells and for cells after exposure to a lens care solution or after mechanical damage by sonication. Exposure to a lens care solution and mechanical cell surface damage reduced the cell surface hydrophobicity and water contact angles decreased from 129 degrees to 96 degrees and 83 degrees, respectively. Zeta potentials in saline (-9 mV) were hardly affected after mechanical damage, but tri-modal zeta potential distributions, with subpopulation zeta potentials at -11, -28 and -41 mV, were observed after exposure of bacteria to a lens care solution. X-ray photoelectron spectroscopy indicated changes in the amounts of oxygen-, nitrogen- and phosphorus-rich cell surface components. Mid-exponential phase cells had more nitrogen-rich cell surface components than early stationary phase cells, but water contact angles and zeta potentials were not very different. In addition, mid-exponential phase cells adhered better than early stationary phase cells to hydrophobic and hydrophilic substrata in a parallel plate flow chamber. The capacity of P. aeruginosa to adhere was decreased after inflicting cell surface damage. Exposure to a lens care solution yielded a larger reduction in adhesion capacity than sonication, likely because sonication left most of the cells in a viable state, in contrast to exposure to a lens care solution. It is argued that for clinically relevant experiments, it may be preferable to work with surface damaged cells rather than with gently harvested organisms.     

Near‐neutral surface charge and hydrophilicity prevent mineral encrustation of Fe‐oxidizing micro‐organisms

Microbial survival in mineralizing environments depends on the ability to evade surface encrustation by minerals, which could obstruct nutrient uptake and waste output. Some organisms localize mineral precipitation away from the cell; however, cell surface properties – charge and hydrophobicity – must also play a role in preventing surface mineralization. This is especially relevant for iron‐oxidizing bacteria (FeOB), which face an encrustation threat from both biotic and abiotic mineralization. We used electron microscopy and surface characterization techniques to study the surfaces of two stalk‐forming neutrophilic FeOB: the marine Zetaproteobacterium Mariprofundus ferrooxydans PV‐1 and the recently isolated freshwater Betaproteobacterium Gallionellales strain R‐1. Both organisms lack detectable iron on cell surfaces. Live and azide‐inhibited M. ferrooxydans PV‐1 cells had small negative zeta potentials (?0.34 to ?2.73 mV), over the pH range 4.2–9.4; Gallionellales strain R‐1 cells exhibited an even smaller zeta potential (?0.10 to ?0.19 mV) over pH 4.2–8.8. Cells have hydrophilic surfaces, according to water contact angle measurements and microbial adhesion to hydrocarbons tests. Thermodynamic and extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) calculations showed that as low charge causes low electrostatic attraction, hydrophilic repulsion dominates cell–mineral interactions. Therefore, we conclude that surface properties help enable these FeOB to survive in highly mineralizing environments. Given both mineral‐repelling surface properties and the ability to sequester Fe(III) biominerals in an organomineral stalk, these two FeOB have a well‐coordinated system to localize both biotic and abiotic mineral distribution.     

Surface properties of calcium phosphate particles for self setting bone cements

Calcium phosphate cements (CPC), consist of multicomponent powder mixtures of calcium orthophosphates with grain sizes in the region of 1-20 microm. Due to the small particle sizes surface properties as the zeta potential and adsorption processes play a significant role during manufacturing and application. In the context of this work zeta potentials of different calcium phosphates, like dicalcium phosphate anhydride (DPCA) tetracalcium phosphate (TTCP) and hydroxyapatite were measured in various organic/aqueous media with different pH values. The results show a strong dependency of the zeta potential on the kind of suspension medium used associated with different milling properties. The addition of sodium phosphate leads to a pH value dependent stabilization of the particles in the liquid phase; the zeta potential of the surface increases from about -15 to -18 mV in water and from -35 to -45 mV in 0.05 mol/l sodium phosphate solution. Besides the interaction of particles with various antibiotics was determined on the basis of the zeta potential of the surface. The substances partly cause a tremendous change of the surface load. This is accompanied by a change of the rheological properties of the cement paste, the morphology of the hardened cement matrix and a significant deterioration of the application-relevant properties as setting time or mechanical strength.     

Molecular characterization of cryptosporidium oocysts in samples of raw surface water and wastewater

Recent molecular characterizations of Cryptosporidium parasites make it possible to differentiate the human-pathogenic Cryptosporidium parasites from those that do not infect humans and to track the source of Cryptosporidium oocyst contamination in the environment. In this study, we used a small-subunit rRNA-based PCR-restriction fragment length polymorphism (RFLP) technique to detect and characterize Cryptosporidium oocysts in 55 samples of raw surface water collected from several areas in the United States and 49 samples of raw wastewater collected from Milwaukee, Wis. Cryptosporidium parasites were detected in 25 surface water samples and 12 raw wastewater samples. C. parvum human and bovine genotypes were the dominant Cryptosporidium parasites in the surface water samples from sites where there was potential contamination by humans and cattle, whereas C. andersoni was the most common parasite in wastewater. There may be geographic differences in the distribution of Cryptosporidium genotypes in surface water. The PCR-RFLP technique can be a useful alternative method for detection and differentiation of Cryptosporidium parasites in water.     

Biothermodynamic analysis of BSA adsorption to alum gel using isothermal titration calorimetry

In this study, we used ITC (isothermal titration calorimetry) to quantitatively investigate the impacts of temperature and protein concentration on adsorption behavior on a solid surface, using BSA (bovine serum albumin) as a model protein, and alum (aluminum hydroxide) gel as an adsorbent. The zeta potential measurement for alum gel (0.25 mV at pH 9.3) revealed that its surface charge was not strong enough for electrostatic interaction. ITC analysis showed that the BSA-alum gel interaction was entropy-driven, suggesting that during adsorption, water molecules were expelled from the hydration layers of the alum gel and BSA. Therefore, the major mechanism for the BSA-alum gel interaction was hydrophobic interaction rather than electrostatic interaction. This biothermodynamic approach can be helpful not only to identify interaction mechanisms, but also to explore the optimum conditions for protein-adsorbent interactions.     

An experimental test of new theoretical models for the electrokinetic properties of biological membranes. The effect of UO2++ and tetracaine on the electrophoretic mobility of bilayer membranes and human erythrocytes

For a large smooth particle with charges at the surface, the electrophoretic mobility is proportional to the zeta potential, which is related to the charge density by the Gouy-Chapman theory of the diffuse double layer. This classical model adequately describes the dependence of the electrophoretic mobility of phospholipid vesicles on charge density and salt concentration, but it is not applicable to most biological cells, for which new theoretical models have been developed. We tested these new models experimentally by measuring the effect of UO2++ on the electrophoretic mobility of model membranes and human erythrocytes in 0.15 M NaCl at pH 5. We used UO2++ for these studies because it should adsorb specifically to the bilayer surface of the erythrocyte and should not change the density of fixed charges in the glycocalyx. Our experiments demonstrate that it forms high-affinity complexes with the phosphate groups of several phospholipids in a bilayer but does not bind significantly to sialic acid residues. As observed previously, UO2++ adsorbs strongly to egg phosphatidylcholine (PC) vesicles: 0.1 mM UO2++ changes the zeta potential of PC vesicles from 0 to +40 mV. It also has a large effect on the electrophoretic mobility of vesicles formed from mixtures of PC and the negative phospholipid phosphatidylserine (PS): 0.1 mM UO2++ changes the zeta potential of PC/PS vesicles (10 mol % PS) from -13 to +37 mV. In contrast, UO2++ has only a small effect on the electrophoretic mobility of either vesicles formed from mixtures of PC and the negative ganglioside GM1 or erythrocytes: 0.1 mM UO2++ changes the apparent zeta potential of PC/GM1 vesicles (17 mol % GM1) from -11 to +5 mV and the apparent zeta potential of erythrocytes from -12 to -4 mV. The new theoretical models suggest why UO2++ has a small effect on PC/GM1 vesicles and erythrocytes. First, large groups (e.g., sugar moieties) protruding from the surface of the PC/GM1 vesicles and erythrocytes exert hydrodynamic drag. Second, charges at the surface of a particle (e.g., adsorbed UO2++) exert a smaller effect on the mobility than charges located some distance from the surface (e.g., sialic acid residues).     

Physicochemical properties of Shiga toxigenic Escherichia coli

AIMS: To investigate the physicochemical surface properties, such as cellular surface charge, hydrophobicity and electron donor/acceptor potential of a selection of Shiga toxigenic Escherichia coli (STEC) isolates grown in broth and agar culture. METHODS AND RESULTS: Cellular surface charge was determined using zeta potential measurements. Hydrophobicity of the isolates was determined using bacterial adhesion to hydrocarbons assay, hydrophobic interaction chromatography and contact angle measurements. Microbial adhesion to solvents was used to determine the electron donor/acceptor characteristics. No differences of surface charge measurements were found between broth and agar grown cultures. Isolates belonging to serogroup O157 and serotypes O26:H11 and O111:H- were significantly (P < 0.05) less negatively charged than other STEC serotypes tested. All strains were hydrophilic with most methods and demonstrated a lower hydrophobicity in agar culture compared with broth culture. All strains demonstrated a strong microbial adhesion to chloroform indicating that STEC possess an electron donor and basic character. A relationship between serogroup O157 and other STEC serotypes was apparent using principal-component analysis (PCA). CONCLUSIONS: Combining the results for physicochemical properties using PCA differentiated between strains belonging to the O157 serogroup and other STEC/non-STEC strains. PCA found similar results for broth and agar grown cultures. SIGNIFICANCE AND IMPACT OF THE STUDY: Particular serotypes of STEC possess similar physicochemical properties which may play a role in their pathogenicity or potential attachment to various surfaces.     

Modifications in erythrocyte membrane zeta potential by Plasmodium falciparum infection

The zeta potential (ZP) is an electrochemical property of cell surfaces that is determined by the net electrical charge of molecules exposed at the surface of cell membranes. Membrane proteins contribute to the total net electrical charge of cell surfaces and can alter ZP through variation in their copy number and changes in their intermolecular interactions. Plasmodium falciparum extensively remodels its host red blood cell (RBC) membrane by placing 'knob'-like structures at the cell surface. Using an electrophoretic mobility assay, we found that the mean ZP of human RBCs was -15.7 mV. In RBCs infected with P. falciparum trophozoites ('iRBCs'), the mean ZP was significantly lower (-14.6 mV, p<0.001). Removal of sialic acid from the cell surface by neuraminidase treatment significantly decreased the ZP of both RBCs (-6.06 mV) and iRBCs (-4.64 mV). Parasite-induced changes in ZP varied by P. falciparum clone and the presence of knobs on the iRBC surface. Variations in ZP values were accompanied by altered binding of iRBCs to human microvascular endothelial cells (MVECs). These data suggest that parasite-derived knob proteins contribute to the ZP of iRBCs, and that electrostatic and hydrophobic interactions between iRBC and MVEC membranes are involved in cytoadherence.     

Physicochemical characterization of Escherichia coli. A comparison with gram-positive bacteria.

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.