Surface free energies of oral streptococci and their adhesion to solids

Abstract The adhesion of 3 strains of oral streptococci from a buffered suspension onto 3 different solid substrata was studied. Representative strains of streptococci were selected on the basis of their surface free energy ( γ _b), namely Streptococcus mitis L1 ( γ _b= 37 mJ·m⁻²), Streptococcus sanguis CH3 (95 mJ·m⁻²) and Streptococcus mutans NS (117 mJ·m⁻²). Solid substrata were also selected on basis of their surface free energy ( γ _s), and included polytetrafluorethylene ( γ _s= 20 mJ·m⁻²), polymethylmethacrylate (53 mJ·m⁻²) and glass (109 mJ·m⁻²). Bacterial adhesion was measured as the number of bacteria adhering per cm² at equilibrium. Equilibrium was usually obtained within 20 min. S. sanguis CH3, having an intermediate surface free energy did not show a clear preference for any of the 3 solids. S. mitis L1, however, the lowest surface free energy strain, adhered in highest numbers to the low energy solid PTFE, whereas the highest γ _b strain, S. mutans NS, adhered in highest numbers to the highest γ _s solid, glass. Calculation of the interfacial free energy of adhesion ( ΔF _adh) for each bacterial strain showed that this parameter was predictive of bacterial adhesion to solid substrata.     

Is the large plasmid of 120 MDa in Shigella sonnei composed of two DNA segments—90 and 30 MDa?

Abstract The reversibility of adhesion of 3 representative strains of oral streptococci from a phosphate-buffered suspension onto 5 different solid substrata was studied.
Streptococcus mitis T9 (surface free energy γ_b= 39 mJ · m⁻²). Streptococcus sanguis CH3 (γ_b= 95 mJ · m⁻²) and Streptococcus mutans NS (γ_b= 117 mJ · m⁻²) were selected on basis of their surface free energy. Solid substrata were employed with a surface free energy γ_s ranging from 20 mJ · m⁻² for polytetrafluorethylene to 109 mJ · m⁻² for glass. Bacterial suspensions containing 2.5 × 10⁹ cells per ml were incubated with 2 samples of each substratum. After 1 h the number of adhering bacteria was evaluated on one sample, while the second sample was kept for another hour at a 10-fold lower bacterial concentration. Bacteria with a low surface free energy desorbed only from substrata with a high surface free energy, while bacteria with a high surface free energy desorbed from substrata with a low surface free energy. Thus low energy bacterial strains adhered reversibly to high energy substrata and vice versa. Similar observations were made with polystyrene particles. Calculation of the interfacial free energy of adhesion (Δ F _adh) for each bacterial strain as well as for the polystyrene particles showed that a reversible adhesion was associated with a positive Δ F _adh, denoting unfavourable adhesion conditions upon a thermodynamic basis.     

Intrafamilial distribution of mutans streptococci in Japanese families and possibility of father-to-child transmission

The purpose of this study was to investigate the intrafamilial distribution of mutans streptococci in Japanese families using chromosomal DNA fingerprinting with three endonucleases; EcoRI, HindIII and HaeIII. The analysis of 1,908 isolates cultured from the dental plaque of 76 subjects from 20 families (20 married couples and 36 of their children) resulted in the identification of 144 genotypes containing 114 strains of Streptococcus mutans (serotype c, 66.7%; e, 12.5%) and 30 strains of S. sobrinus (d, 13.2%; g, 7.6%). A mean of 1.89 genotypes (from one to four) was harbored in individual subjects, and a mean of 4.10 genotypes from two to seven was harbored in individual families. Among the 70 genotypes found in the children, 36 (51.4%) were in agreement with their mothers and 22 (31.4%) were in agreement with their fathers. The other genotypes (18.6%) did not correspond with the parents. Homologous strains between parents were found in only two couples. This result showed that fathers or others as well as mothers can be sources of transmission. Further, the serotype d, e and g strains showed significantly higher probabilities of transmission than serotype c.     

Biodeterioration of dental materials: Influence of bacterial adherence

The aim of this work was to carry out a comparative study of microbial adhesion on dental alloys and glass ionomers that release fluoride. The action of NaF on the early stages of biofilm development and on the corrosion of the metallic dental materials was analysed. Open circuit potential measurements and potentiostatic electrochemical techniques with different perturbation programs as well as SEM observations, and optical and epifluorescence microscopy were employed. A notable effect of topography and the nature of the substratum on bacterial distribution was observed. In addition, changes in the density and thickness of microbial colonies were noticed when fluoride was present. The results show that the antimicrobial effect of fluoride was significant against planktonic but not against sessile microorganisms. Fluoride released by glass ionomers did not impede bacterial adhesion to the surface. With respect to corrosion, fluoride did not alter significantly the passivity of the dental metallic biomaterials assayed, except for Cu‐Al alloy. Titanium dissolution could occur at high fluoride concentrations (8gl^‐1) during oxide layer formation. Consequently, bacterial adherence was influenced by the nature and topography of the substratum and by the presence of fluoride which could also affect the electrochemical behaviour of some metallic substrata.     

Nonequilibrium chemical potentials and free energies for enzyme-catalyzed reactions

Using the statistical theory of nonequilibrium thermodynamics we explore the nature of nonequilibrium corrections to chemical potentials in simple enzyme-catalyzed reactions. The statistical definition of the chemical potential, which pertains to systems that are at stable steady states, is applied to the Michaelis-Menten reaction scheme in a cellular-sized compartment that communicates with out-side reservoirs. Calculations based on the kinetic parameters for hexokinase and triose phosphate isomerase show that substantial corrections to the chemical potential of product (the order of 25 mV) are possible if the reaction is sufficiently far from equilibrium. The dependence of the corrections to the chemical potentials on the size of the cellular compartment are explored, and the relevance of the corrections for understanding the thermodynamics of metabolites is discussed.     

Proteolytic activity of oral streptococci

Streptococcus mutans and Streptococcus sobrinus were the least proteolytic of 8 species of oral streptococci while Streptococcus oralis and Streptococcus sanguis were the most proteolytic. Degradation of FITC-BSA was significantly correlated with the hydrolysis of synthetic endopeptidase substrates. As S. oralis strains proliferate in dental plaque in the absence of dietary food their success, in vivo, might be due partially to their greater proteolytic activity compared to other oral streptococci.     

Crystalline anatase-rich titanium can reduce adherence of oral streptococci

Dental implant abutments that emerge through the mucosa are rapidly covered with a salivary protein pellicle to which bacteria bind, initiating biofilm formation. In this study, adherence of early colonizing streptococci, Streptococcus gordonii, Streptococcus oralis, Streptococcus mitis and Streptococcus sanguinis to two saliva-coated anodically oxidized surfaces was compared with that on commercially pure titanium (CpTi). Near edge X-ray absorption (NEXAFS) showed crystalline anatase was more pronounced on the anodically oxidized surfaces than on the CpTi. As revealed by fluorescence microscopy, a four-species mixture, as well as individual bacterial species, exhibited lower adherence after 2?h to the saliva-coated, anatase-rich surfaces than to CpTi. Since wettability did not differ between the saliva-coated surfaces, differences in the concentration and/or configuration of salivary proteins on the anatase-rich surfaces may explain the reduced bacterial binding effect. Anatase-rich surfaces could thus contribute to reduced overall biofilm formation on dental implant abutments through diminished adherence of early colonizers.     

Estimates of Gibbs free energies of formation of chlorinated aliphatic compounds

The Gibbs free energy of formation of chlorinated aliphatic compounds was estimated with Mavrovouniotis' group contribution method. The group contribution of chlorine was estimated from the scarce data available on chlorinated aliphatics in the literature, and found to vary somewhat according to the position of chlorine in the molecule. The resulting estimates of the Gibbs free energy of formation of chlorinated aliphatic compounds indicate that both reductive dechlorination and aerobic mineralization of these compounds can yield sufficient energy to sustain microbial growth.     

In vitro binding interactions of oral bacteria with immobilized fructosyltransferase

AIMS: The objective of the present study was to explore the role of immobilized fructosyltransferase (FTF) in adhesion process. METHODS AND RESULTS: We investigated real-time biospecific interactions between several types of oral bacteria and recombinant FTF immobilized on a biosensor chip, using surface plasmon resonance technology. Streptococcus mutans, Streptococcus sobrinus and Actinomyces viscosus demonstrated significant binding to FTF. Actinomyces viscosus had a greater binding to FTF, with 373 Resonance Units (RU), than the other tested bacteria. The binding level to FTF of Strep. sobrinus was 320 RU, whereas Strep. mutans and Streptococcus salivarious show binding of 296 and 245 RU, respectively. The binding sensograms displayed different profiles for the tested bacteria at various cell density, suggesting a different affinity to immobilized FTF. CONCLUSIONS: The results from this study suggest that FTF may influence bacterial adherence and colonization of the dental biofilm. SIGNIFICANCE AND IMPACT OF THE STUDY: The biomolecular interaction analysis enables real-time monitoring of the interaction between adhesions of intact bacteria and their ligands, which might be crucial in the initial phase of biofilm development in vivo.     

Thermodynamic aspects of cell spreading on solid substrata

To verify the validity of thermodynamic approaches to the prediction of cellular behavior, cell spreading of three different cell types on solid substrata was determined in vitro. Solid substrata as well as cell types were selected on the basis of their surface free energies, calculated from contact angle measurements. The surface free energies of the solid substrata ranged from 18–116 erg cm⁻². To measure contact angles on cells, a technique was developed in which a multilayer of cells was deposited on a filter and air dried. Cell surface free energies ranged from 60 erg cm⁻² for fibroblasts, and 57 for smooth muscle cells, to 91 for HeLa epithelial cells. After adsorption of serum proteins, cell surface free energies of all three cell types converged to approx 74 erg cm⁻². The spreading of these cell types from RPMI 1640 medium on the various solid substrata showed that both in the presence and in the absence of serum proteins in the medium, cells spread poorly on low energy substrata (Y _s <50 erg cm⁻²), whereas good cell spreading was observed on the higher energy substrata. Calculations of the interfacial free energy of adhesion (ΔF _adh) show that ΔF _adh decreases with increasingY _s , and equals zero around 45 erg cm⁻² for all three cell types in the presence of serum proteins and for HeLa epithelium cells in the absence of serum proteins. This explains the spreading of these cells on the various substrata upon a thermodynamic basis. The results clearly show that substratum surface free energy has a predictive value with respect to cell spreading in vitro, both in the presence and absence of serum proteins. It is noted, however, that interfacial thermodynamics fail to explain the behavior of fibroblasts and smooth muscle cells in the absence of serum proteins, most likely because of the relatively high surface charges of these two cell types.     

Solvation free energies of nucleic acid bases in ionic liquids

The solvation free energies of five nucleic acid bases in [C_nbim]Br (where n = 2, 4, 6) ionic liquids (ILs) were computed using the Bennett acceptance ratio (BAR) method employing molecular dynamics simulations. The computed free energies using BAR were in agreement with other methods. The large and negative predicted free energies of the bases in ILs indicated that the bases were better solvated in the ILs rather than in water. Hydrogen bonding interactions between polar sites of the bases and ILs’ ions significantly contributed to the solvation mechanism.     

On the calculation of binding free energies using continuum methods: Application to MHC class I protein-peptide interactions

This paper describes a methodology to calculate the binding free energy (ΔG) of a protein-ligand complex using a continuum model of the solvent. A formal thermodynamic cycle is used to decompose the binding free energy into electrostatic and non-electrostatic contributions. In this cycle, the reactants are discharged in water, associated as purely nonpolar entities, and the final complex is then recharged. The total electrostatic free energies of the protein, the ligand, and the complex in water are calculated with the finite difference Poisson-Boltzmann (FDPB) method. The nonpolar (hydrophobic) binding free energy is calculated using a free energy-surface area relationship, with a single alkane/water surface tension coefficient (γ_aw). The loss in backbone and side-chain configurational entropy upon binding is estimated and added to the electrostatic and the nonpolar components of ΔG. The methodology is applied to the binding of the murine MHC class I protein H-2K^b with three distinct peptides, and to the human MHC class I protein HLA-A2 in complex with five different peptides. Despite significant differences in the amino acid sequences of the different peptides, the experimental binding free energy differences (ΔΔG_exp) are quite small (<0.3 and <2.7 kcal/mol for the H-2K^b and HLA-A2 complexes, respectively). For each protein, the calculations are successful in reproducing a fairly small range of values for ΔΔG_calc (<4.4 and <5.2 kcal/mol, respectively) although the relative peptide binding affinities of H-2K^b and HLA-A2 are not reproduced. For all protein-peptide complexes that were treated, it was found that electrostatic interactions oppose binding whereas nonpolar interactions drive complex formation. The two types of interactions appear to be correlated in that larger nonpolar contributions to binding are generally opposed by increased electrostatic contributions favoring dissociation. The factors that drive the binding of peptides to MHC proteins are discussed in light of our results.     

Surface free energy and interaction of Staphylococcus epidermidis with biomaterials

The adhesion of twenty nine Staphylococcus epidermidis strains to teflon, polyethylene, polycarbonate and bovine pericardium was studied in vitro and examined in relation to the surface free energies of both bacteria and biomaterials. All S. epidermidis strains had similar surface free energies, close to that of water, and adhered better to the materials with analogous surface free energies. There was a significant correlation (Kendall's Tau B = 1000) of biomaterial's surface free energy with the number of adhering bacteria. This correlation is inverse (Kendall's Tau B = -1000) when surface hydrophobicity is considered instead of surface free energy. This indicates that in Staphylococcus epidermidis adherence to biomaterials is inversely correlated to the surface hydrophobicity of the last, being so just the opposite of that occurring with other bacteria.     

Interfacial free energies of intact and reconstituted erythrocyte surfaces: Implications for biological adhesion

Model cell surfaces consisting of phospholipids or phospholipids and the erythrocyte membrane glycoprotein glycophorin have been formed at an oil/water interface. Interfacial free energies have been estimated from surface wetting by both hydrophobic and hydrophilic test droplets on both the model surfaces and on intact erythrocytes. The use of a dense fluorocarbon oil to form the oil/water interface facilitates analysis by minimising surface deformation by the test drop. Hydrophobic test droplets (polar hydrocarbon oils) show increasing contact angles (decreasing wetting) with increasing hydrophilicity (decreasing interfacial free energy) of the model interface. Hydrophilic test droplets (phase separated aqueous polymer systems) show the opposite behaviour, spreading more as the interfacial free energy is decreased. Both systems give similar estimates of the interfacial free energy. Glycophorin reproduces the wetting properties of intact cell surfaces by reducing the lipid-water interfacial free energy from 5·10^?3 J·m^?2 to 1·10^?6 J·m^?2. From molecular considerations it is concluded that ‘cell surface free energy’ is an ambiguous term; its magnitude depends on the location of the interface in question. Thus, in a thermodynamic analysis of interactions at biosurfaces (such as cellular adhesion, chemotaxis or membrane fusion), the interfacial free energies may vary by more than three orders of magnitude depending on the location of the particular interface.     

表面自由能在环境微生物粘附研究中的应用进展

在环境领域中,对微生物粘附的利用和控制越来越受到研究者的关注。其中,微生物的表面自由能作为细胞表面重要特性,对微生物的粘附行为有重要影响。本文总结了微生物粘附过程中涉及的热动力学理论、Derjaguin-Landau-Verwey-Overbeek(DLVO)以及扩展DLVO理论,阐述了微生物表面自由能在该过程的重要性。基于此,介绍了接触角表征微生物表面自由能的方法体系及影响因素;分析了微生物表面自由能及其分量的分布特征、与物质组成的关系。最后根据被粘附对象的不同,总结了环境微生物表面自由能在固体基质、液体基质或者微生物相互之间粘附中的应用;指出未来研究发展的方向应关注环境微生物表面自由能的标准化表征及其在复杂环境中的应用。     

An efficient protocol for obtaining accurate hydration free energies using quantum chemistry and reweighting from molecular dynamics simulations

The non-Boltzmann Bennett (NBB) free energy estimator method is applied to 21 molecules from the blind subset of the SAMPL4 challenge. When NBB is applied with the SMD implicit solvent model, and the OLYP/DZP level of quantum chemistry, highly accurate hydration free energy calculations are obtained with respect to experiment (RMSD = 0.89 kcal·mol⁻¹). Other quantum chemical methods are also tested, and the effects of solvent model, density functional, basis set are explored in this benchmarking study, providing a framework for improvements in calculating hydration free energies. We provide a practical guide for using the best QM-NBB protocols that are consistently more accurate than either pure QM or pure MM alone. In situations where high accuracy hydration free energy predictions are needed, the QM-NBB method with SMD implicit solvent should be the first choice of quantum chemists.     

Differential adhesive properties of the surface of human blood flukesSchistosoma mansoni

While infecting a vertebrate host, blood flukes (Schistosoma mansoni) must continually resist adhesions by immune effector cells. However, the male and female schistosomes must adhere to one another in order to establish and maintain the sexual pairing process after 4 wk postinfection. Using a contact angle method, the relative adhesiveness of male and female parasites were determined. Results indicate that schistosomes restrict effector cell adhesion through developmental, sexual, and regional differences in adhesive properties.     

Prediction of protein-protein binding free energies

We present an energy function for predicting binding free energies of protein-protein complexes, using the three-dimensional structures of the complex and unbound proteins as input. Our function is a linear combination of nine terms and achieves a correlation coefficient of 0.63 with experimental measurements when tested on a benchmark of 144 complexes using leave-one-out cross validation. Although we systematically tested both atomic and residue-based scoring functions, the selected function is dominated by residue-based terms. Our function is stable for subsets of the benchmark stratified by experimental pH and extent of conformational change upon complex formation, with correlation coefficients ranging from 0.61 to 0.66.     

Synergistic degradation of bovine serum albumin by mutans streptococci and other dental plaque bacteria

Mutans streptococci (Streptococcus mutans and Streptococcus sobrinus) exhibited low levels of proteolytic activity against the model protein substrate, FITC-labelled bovine serum albumin, when incubated alone. Inclusion of other members of the dental plaque microflora in the assay usually resulted in marked increases in the degree of proteolysis and a high level of synergy. Interactions between mutans streptococci and either Streptococcus oralis or Fusobacterium nucleatum gave rise to the greatest degree of synergistic proteolytic degradation.