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Surface structures in the nanometer range emerge as the next evolutionary breakthrough in the design of biomaterials with antimicrobial properties. However, in order to advance the application of surface nanostructuring strategies in medical implants, the very nature of the microbial repealing mechanism has yet to be understood. Herein, we demonstrate that the random immobilization of gold nanoparticles (AuNPs) on a material's surface generates the possibility to explore microbial adhesion in dependence of contact point densities at the biointerface between the microbe, i.e., Escherichia coli and the material's surface. By optimizing the contact point density defined by individual AuNPs, yet keeping the surface chemistry unchanged as evidenced by X-ray photoelectron spectroscopy, we show that the initial microbial adhesion can be successfully reduced up to 50%, compared to control (unstructured) surfaces. Furthermore, we observed a decrease in the size of microbial cells adhered to nanostructured surfaces. The results show that the spatial distance between the contact points plays a crucial role in regulating microbial adhesion, thus advancing our understanding of the microbial adhesion mechanism on nanostructured surfaces. We suggest that the introduced strategy for nanostructuring materials surfaces opens a research direction for highly microbial-resistant biomaterials.

Cell hydrophobicity is one of the key physicochemical properties of bacteria in activated sludge (AS) and biofilms can influence the efficient operation of wastewater treatment plants (WWTPs). In the present study the cell hydrophobicity of diverse bacterial populations in AS and biofilms from the Shatin and Stanley WWTPs of Hong Kong was characterized by combining the microbial adhesion to hydrocarbons (MATH) assay with the Illumina high-throughput sequencing. The results indicated that, at the phylum level, a majority of bacteria in AS and biofilms showed medium hydrophobicity. Most of the top 20 bacterial genera in the AS samples were hydrophilic. However, the top 20 genera in biofilms showed higher hydrophobicity than in the top 20 genera in AS samples, suggesting more hydrophobic bacteria existed in biofilms than in AS. Meanwhile, the hydrophobicity of two specific bacterial groups, including foaming and biosurfactant-producing bacteria, were also evaluated. The results demonstrated that, by combining the MATH assay with the Illumina sequencing approach, bacterial hydrophobicity could be evaluated with high efficiency and coverage in complex systems with high microbial diversity, e.g. AS and biofilms in WWTPs.

Poly(dimethyl siloxane) (PDMS) was surface-polymerized with poly(ethylene glycol)methacrylate (PEGMA) by surface-initiated atom transfer radical polymerization (SI-ATRP) in aqueous media at room temperature. Modification of the PDMS surface followed a three-step procedure: (i) PDMS surface hydroxylation by UV/ozone exposure, immediately followed by (ii) covalent attachment of the initiator, 1-trichlorosilyl-2-(chloromethylphenyl)ethane, onto the hydroxylated PDMS, via chemical vapor deposition; finally (iii) PDMS surface-polymerization of PEGMA by ATRP. Modified PDMS was characterized by water contact angle measurement, SEM, FTIR-ATR, and XPS. Results showed that modified surfaces had a hydrophilic character, given the water contact angles around 60◦; FTIR-ATR and XPS analysis confirmed the presence of polymerized PEGMA on the surface of PDMS and the adhesion of Staphylococcus aureus GB 2/1 and Streptococcus salivarius GB 24/9 onto the modified surfaces was inhibited 94% and 81%, respectively. Finally, the modified PDMS showed no evidence of cytotoxic effects in in vitro assays using human skin fibroblasts., The authors acknowledge Stockwell Elastomerics Inc. for kindly proving the silicone rubber samples (ref. HT6240). SEM, FTIR-ATR and XPS studies were performed at SEMAT (University of Minho, Portugal), DEP (University of Minho, Portugal) and CEMUP (University of Porto, Portugal) facilities, respectively. Also, the authors acknowledge the financial support from Fundacao para a Ciencia e Tecnologia (FCT) to the project BIOSURFA - Application of biosurfactants for microbial adhesion inhibition in medical devices (PTDC/SAU-BEB/73498/2006).

The physicochemical surface properties of blastospores of the entomopathogenic fungus Paecilomyces fumosoroseus were examined. Contact angle measurements were performed on microbial lawns composed of blastospores of P. fumosoroseus to quantify their cell surface energy components. In addition, suspensions of the blastospores were characterized with the microbial adhesion to solvents assay. Zeta potential measurements were used to quantify the surface charge and determine the zero potential of the blastospores. The results show blastospores of P. fumosoroseus are best described as having a basic monopolar surface and classified as hydrophilic. Blastospores are also negatively charged under neutral conditions with an isoelectric point of 3.4.

Microbial adhesion to surfaces often occurs despite high wall shear rates acting on the adhering microorganisms. In this paper, we compare the wall shear rates needed to prevent microbial adhesion to bare glass and poly(ethylene oxide) (PEO)-brush coated glass in a parallel plate flow chamber. Initial microbial deposition rates were determined for different wall shear rates between 4 and 1600 s(-1) on the top and bottom plates of the flow chamber. Deposition efficiencies alpha(SL), based on the Stroluchowski-Levich approach, for Pseudomonas aeruginosa D1, Escherichia coli O2K2 and Candida tropicalis GB 9/9 decreased with increasing wall shear rates and were lower for PEO-brush coated glass than for bare glass. Characteristic shear rates preventing adhesion to the bottom plate were around 10 and 1.0 s(-1) for the bacteria on glass and the PEO-brush and 36 and 3.4 s-1 for the yeast strain on glass and the PEO-brush, respectively. This demonstrates that the adhesive forces between microorganisms and a PEO-brush are comparatively weak, although some strains may have the ability to adhere to a PEO-brush under low shear conditions. Microbial deposition efficiencies alpha(SL) were much larger, however, than unity for bottom plate deposition, but Could be reduced to realistic values by averaging the deposition rates found for the top (negative contribution of sedimentation) and bottom (positive contribution of sedimentation) plates. (c) 2005 Elsevier B.V. All rights reserved.

Microbial adhesion to surfaces often occurs despite high wall shear rates acting on the adhering microorganisms. In this paper, we compare the wall shear rates needed to prevent microbial adhesion to bare glass and poly(ethylene oxide) (PEO)-brush coated glass in a parallel plate flow chamber. Initial microbial deposition rates were determined for different wall shear rates between 4 and 1600 s(-1) on the top and bottom plates of the flow chamber. Deposition efficiencies alpha(SL), based on the Stroluchowski-Levich approach, for Pseudomonas aeruginosa D1, Escherichia coli O2K2 and Candida tropicalis GB 9/9 decreased with increasing wall shear rates and were lower for PEO-brush coated glass than for bare glass. Characteristic shear rates preventing adhesion to the bottom plate were around 10 and 1.0 s(-1) for the bacteria on glass and the PEO-brush and 36 and 3.4 s-1 for the yeast strain on glass and the PEO-brush, respectively. This demonstrates that the adhesive forces between microorganisms and a PEO-brush are comparatively weak, although some strains may have the ability to adhere to a PEO-brush under low shear conditions. Microbial deposition efficiencies alpha(SL) were much larger, however, than unity for bottom plate deposition, but Could be reduced to realistic values by averaging the deposition rates found for the top (negative contribution of sedimentation) and bottom (positive contribution of sedimentation) plates. (c) 2005 Elsevier B.V. All rights reserved.

International audience; The aim of the present investigation was to compare the in vitro bacterial retention on saliva-coated implant materials (pure titanium grade 2 (cp-Ti) and a titanium alloy (Ti-6Al-4V) surfaces), presenting similar surface roughness, and to assess the influence of physico-chemical surface properties of bacterial strain and implant materials on in vitro bacterial adherence. Two bacterial strains (one hydrophilic strain and one hydrophobic strain) were used and the following were evaluated: bacterial cell adherence, SFE values as well as the Lifshitz-van-der Waals, the Lewis acid base components of SFE, the interfacial free energy and the non-dispersive interactions according to two complementary contact angle measurement methods: the sessile drop method and the captive bubble method. Our results showed similar patterns of adherent bacterial cells on saliva-coated cp-Ti and saliva-coated Ti-6Al-4V. These findings could suggest that bacterial colonization (i.e. plaque formation) is similar on saliva-coated cp-Ti and Ti-6Al-4V surfaces and indicate that both materials could be suitable for use as transgingival abutment or healing implant components. The same physico-chemical properties exhibited by saliva-coated cp-Ti and TAW, as shown by the sessile drop method and the captive bubble method, could explain this similar bacterial colonisation. Therefore, higher values of total surface free energy of saliva-coated cp-Ti and saliva-coated TA6V samples (gamma(sv) approximate to65 mJ/m(2)) were reported using the captive bubble method indicating a less hydrophobic character of these surfaces than with the sessile drop method (gamma(s) approximate to44.50 mJ/m(2)) and consequently possible differences in oral bacterial retention according the theory described by Absolom et al. The number of adherent hydrophobic S. sanguinis cells was two-fold higher than that of hydrophilic S. constellatus cells. Our results confirm that physico-chemical surface properties of oral bacterial strains play a role in bacterial retention to implant materials in the presence of adsorbed salivary proteins. (C) 2004 Elsevier B.V. All rights reserved.

Deposition of three marine bacterial strains with different cell surface hydrophobicities from artificial seawater to polyurethane coatings on glass with different surface tensions and elastic modulus was studied in situ in a parallel plate (PP) and stagnation point (SP) flow chamber. Different surface tensions of the coatings were established by changing the amount of fluorine, whereas using more or less branched polymers made different elastic moduli. Surface tensions of the coating, derived from measured contact angles with liquids, ranged from 11.9 to 44.9 mJ m(-2), while the elastic moduli, derived from force-distance curves as measured with an atomic force microscope were between 1.5 and 2.2 GPa. In both flow chambers, the most hydrophilic bacterium Halomonas pacifica adhered preferentially to the more hydrophilic, non-fluoridated coating, whereas the most hydrophobic bacterium Marinobacter hydrocarbonoclasticus showed a greater preference for the more hydrophobic coating. Bacterial adhesion in the PP flow chamber was not influenced by the elastic modulus of the coatings, but in the SP flow chamber bacteria adhered in higher numbers to hard surfaces than to coatings of lower elastic moduli. (C) 2003 Elsevier B.V. All rights reserved.

Cell surface hydrophobicity is one of the most important factors controlling adhesion of microorganisms to surfaces. In this paper, cell surface properties of lactobacilli and recombinant lactobacilli with and without a surface layer protein (SLP) associated with cell surface hydrophobicity were determined, including water contact angles, zeta potentials as a function of pH, the nitrogen contents of the cell surface and adhesion to hexadecane. Two strains possessing an S-layer (Lactobacillus acidophilus ATCC4356 and L. crispatus JCM5810) showed the highest water contact angles (76 and 55degrees, respectively) and the highest N/C surface concentration ratios by X-ray photoelectron spectroscopy (0.172 and 0.160, respectively), indicative of the presence of S-layer proteins. L. casei 393*/CA5'A, with the SLP of L. crispatus JCM5810 anchored to its surface had higher water contact angles (62degrees) than its parent strain (32degrees). but no higher amount of cell surface nitrogen. However, anchoring of the SLP did stimulate its adhesion to hexadecane. LiCl treatment, removing Slayer and other non-covalently linked surface proteins, increased water contact angles and N/C ratios for L. crispatus JCM5810 and L. casei 393*/CA5'A, while L. acidophilus ATCC4356 showed a decrease in the N/C ratio like for L. gasseri LMG9203, that lacks an SLP. The isoelectric point of all but one Lactobacillus strain varied between 3.2 and 4.6, whereas strain L. crispatus JCM5810 was positively charged over the entire pH range. A hierarchical cluster analysis, using all cell surface hydrophobicity associated properties as input, yielded one cluster for strains possessing SLP, well separated from the other strains, including strains secreting SLP. It is concluded that SLP conveys hydrophobicity to the Lactobacillus cell surface and enhances its adhesion to hexadecane through hydrophobic interactions. (C) 2002 Elsevier Science B.V. All rights reserved.

Cell surface hydrophobicity is one of the most important factors controlling adhesion of microorganisms to surfaces. In this paper, cell surface properties of lactobacilli and recombinant lactobacilli with and without a surface layer protein (SLP) associated with cell surface hydrophobicity were determined, including water contact angles, zeta potentials as a function of pH, the nitrogen contents of the cell surface and adhesion to hexadecane. Two strains possessing an S-layer (Lactobacillus acidophilus ATCC4356 and L. crispatus JCM5810) showed the highest water contact angles (76 and 55degrees, respectively) and the highest N/C surface concentration ratios by X-ray photoelectron spectroscopy (0.172 and 0.160, respectively), indicative of the presence of S-layer proteins. L. casei 393*/CA5'A, with the SLP of L. crispatus JCM5810 anchored to its surface had higher water contact angles (62degrees) than its parent strain (32degrees). but no higher amount of cell surface nitrogen. However, anchoring of the SLP did stimulate its adhesion to hexadecane. LiCl treatment, removing Slayer and other non-covalently linked surface proteins, increased water contact angles and N/C ratios for L. crispatus JCM5810 and L. casei 393*/CA5'A, while L. acidophilus ATCC4356 showed a decrease in the N/C ratio like for L. gasseri LMG9203, that lacks an SLP. The isoelectric point of all but one Lactobacillus strain varied between 3.2 and 4.6, whereas strain L. crispatus JCM5810 was positively charged over the entire pH range. A hierarchical cluster analysis, using all cell surface hydrophobicity associated properties as input, yielded one cluster for strains possessing SLP, well separated from the other strains, including strains secreting SLP. It is concluded that SLP conveys hydrophobicity to the Lactobacillus cell surface and enhances its adhesion to hexadecane through hydrophobic interactions. (C) 2002 Elsevier Science B.V. All rights reserved.

The effects of growth in the presence of sub-inhibitory concentrations of ampicillin and vancomycin on physicochemical cell surface properties of Enterococcus jaecalis 1131 have been determined. Growth in the presence of antibiotics yielded increased exposure of nitrogen and oxygen at the cell surface, proportional to the amount of antibiotic added to the growth medium, probably as a result of progressive removal of lipoteichoic acid (LTA) by ampicillin and vancomycin. Bacterial isoelectric points (IEP's), derived from particulate microelectrophoresis at different suspension pH, increased concurrently. Water contact angles on bacterial lawns only varied slightly in the presence of antibiotic during growth, whereas formamide contact angles after growth in the presence of vancomycin were significantly higher than after growth in the absence of this antibiotic, yielding a strongly electron-donating character of the cell surface. Surface thermodynamical analyses indicated favourable conditions for adhesion to hexadecane and chloroform, but more negative values of interaction free energies did not necessarily coincide with increased adhesion. Bacterial adhesion to hexadecane and chloroform increased when the pH of the bacterial suspension approached the isoelectric point of the organisms, because of the minimal electrostatic interactions. (C) 2002 Elsevier Science B.V. All rights reserved.

Calcium is an abundantly present, divalent cation in the oral cavity and plays a crucial role in the adhesion of oral microorganisms to tooth surfaces as well as in coaggregation and coadhesion among the oral microflora. The aim of this study was to determine the effects of divalent cation (Ca2+, Mg2+, Ba2+ adsorption on the adhesion of two actinomyces and two streptococcal strains to hexadecane (MATH) and chloroform (MATS) in order to detect changes in acid-base character of the cell surfaces. Initial removal rates of the organisms by hexadecane, lacking an acid-base interaction with the organisms, were always smaller than those by chloroform. Furthermore, adsorption of divalent cations generally increased the initial removal rates of the microorganisms, but no statistically significant differences among different cations were observed. Gibbs energies of partitioning calculated from the stationary end-point adhesion of the organisms ranged from -2 to -4 kT for adhesion to hexadecane and were about twofold more negative for adhesion to chloroform. Contact angles on lawns of microorganisms with and without adsorbed divalent cations were similar. Zeta potentials of all microorganisms were slightly negative under the conditions of MATH and MATS and became only 4 mV more positive upon divalent cation adsorption. Hexadecane had a zeta potentials of -21 mV in the potassium phosphate solution used, which became 13 mV less negative upon Ca2+ adsorption. An extended DLVO approach of microbial adhesion to hexadecane, based on microbial contact angles and zeta potentials, taking into account Lifshitz-van der Waals, acid-base and electrostatic interactions did not show any potential energy barrier and demonstrated a deep primary interaction minimum at close approach due to acid-base attraction. As the Gibbs energy of partioning was only -2 to -4 kT, it is concluded that for the collection of organisms studied here, the final contactable surface area is small and structural features on the cell surfaces like fibrils and fimbriae, maintain a distance of ca. 10-15 nm between the hexadecane and the overall cell surface and therewith prevent acid-base interactions to become operative to a significant extend. Furthermore, from the lack of influence of divalent cations on macroscopic cell surface contact angles and zeta potentials, it is suggested that cation adsorption is minor and localized to the fibrils and fimbriae. (C) 1999 Elsevier Science B.V. All rights reserved.

Calcium is an abundantly present, divalent cation in the oral cavity and plays a crucial role in the adhesion of oral microorganisms to tooth surfaces as well as in coaggregation and coadhesion among the oral microflora. The aim of this study was to determine the effects of divalent cation (Ca2+, Mg2+, Ba2+ adsorption on the adhesion of two actinomyces and two streptococcal strains to hexadecane (MATH) and chloroform (MATS) in order to detect changes in acid-base character of the cell surfaces. Initial removal rates of the organisms by hexadecane, lacking an acid-base interaction with the organisms, were always smaller than those by chloroform. Furthermore, adsorption of divalent cations generally increased the initial removal rates of the microorganisms, but no statistically significant differences among different cations were observed. Gibbs energies of partitioning calculated from the stationary end-point adhesion of the organisms ranged from -2 to -4 kT for adhesion to hexadecane and were about twofold more negative for adhesion to chloroform. Contact angles on lawns of microorganisms with and without adsorbed divalent cations were similar. Zeta potentials of all microorganisms were slightly negative under the conditions of MATH and MATS and became only 4 mV more positive upon divalent cation adsorption. Hexadecane had a zeta potentials of -21 mV in the potassium phosphate solution used, which became 13 mV less negative upon Ca2+ adsorption. An extended DLVO approach of microbial adhesion to hexadecane, based on microbial contact angles and zeta potentials, taking into account Lifshitz-van der Waals, acid-base and electrostatic interactions did not show any potential energy barrier and demonstrated a deep primary interaction minimum at close approach due to acid-base attraction. As the Gibbs energy of partioning was only -2 to -4 kT, it is concluded that for the collection of organisms studied here, the final contactable surface area is small and structural features on the cell surfaces like fibrils and fimbriae, maintain a distance of ca. 10-15 nm between the hexadecane and the overall cell surface and therewith prevent acid-base interactions to become operative to a significant extend. Furthermore, from the lack of influence of divalent cations on macroscopic cell surface contact angles and zeta potentials, it is suggested that cation adsorption is minor and localized to the fibrils and fimbriae. (C) 1999 Elsevier Science B.V. All rights reserved.

Adhesion of microorganisms to various interfaces has been explained by the classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory of colloid stability. The theory has been used as a qualitative model, but also in a quantitative way to calculate adhesion free energy changes involved in microbial adhesion. In this paper some important investigations will be review that show how the DLVO theory is used in microbiology, mainly for bacteria. Other models have also been developed in order to predict adhesion, such as the thermodynamic approach and later the extended DLVO theory. These will be discussed in relation to the ‘classical’ DLVO theory. The theories assume that microbial cells behave as inert particles. The implications that follow from the fact that they are biologically active and have heterogeneous cell surfaces will also be exemplified and discussed.

Indwelling voice prostheses are most often made of silicone rubber. However, the silicone rubber surface attracts huge quantities of adhering yeasts and bacteria and their colonization on the valve side of voice prostheses leads to frequent malfunctioning. On average, indwelling voice prostheses have to be replaced every three to four months. In this paper, we report on the in vitro adhesion of yeasts and bacteria to fluoro-alkylsiloxane layers chemisorbed on silicone rubber surfaces, as measured in a parallel plate flow chamber. Silicone rubber surfaces were first oxidized with an argon plasma treatment (Ar-SR). In a second step, organic layers were created by chemisorption of fluoroalkyltrichlorosilanes onto the Ar-SR surfaces, denoted as Ar-SR-CF3 and Ar-SR-C8F17, respectively. Physico-chemical properties of the chemisorbed layers were studied by using water contact angle measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Using a parallel plate flow chamber, adhesion of Streptococcus salivarius, Staphylococcus epidermidis, Candida albicans and Candida tropicalis strains, isolated from explanted voice prostheses, was investigated to the chemisorbed fluoroalkylsiloxane layers with and without a salivary conditioning film. Ar-SR-CF3 and Ar-SR-C8F17 surfaces showed significantly reduced microbial adhesion as compared to original silicone rubber, both with respect to initial deposition rates and adhesion in a stationary end-point. Furthermore, adhering microorganisms were more easily detached when applying an air-liquid interface. Silicone rubber surfaces with chemisorbed, long fluorocarbon chains (Ar-SR-C8F17) showed the greatest reduction in microbial adhesion, probably because of their low surface free energy combined with a higher surface mobility. (C) 1998 Elsevier Science B.V.

Indwelling voice prostheses are most often made of silicone rubber. However, the silicone rubber surface attracts huge quantities of adhering yeasts and bacteria and their colonization on the valve side of voice prostheses leads to frequent malfunctioning. On average, indwelling voice prostheses have to be replaced every three to four months. In this paper, we report on the in vitro adhesion of yeasts and bacteria to fluoro-alkylsiloxane layers chemisorbed on silicone rubber surfaces, as measured in a parallel plate flow chamber. Silicone rubber surfaces were first oxidized with an argon plasma treatment (Ar-SR). In a second step, organic layers were created by chemisorption of fluoroalkyltrichlorosilanes onto the Ar-SR surfaces, denoted as Ar-SR-CF3 and Ar-SR-C8F17, respectively. Physico-chemical properties of the chemisorbed layers were studied by using water contact angle measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Using a parallel plate flow chamber, adhesion of Streptococcus salivarius, Staphylococcus epidermidis, Candida albicans and Candida tropicalis strains, isolated from explanted voice prostheses, was investigated to the chemisorbed fluoroalkylsiloxane layers with and without a salivary conditioning film. Ar-SR-CF3 and Ar-SR-C8F17 surfaces showed significantly reduced microbial adhesion as compared to original silicone rubber, both with respect to initial deposition rates and adhesion in a stationary end-point. Furthermore, adhering microorganisms were more easily detached when applying an air-liquid interface. Silicone rubber surfaces with chemisorbed, long fluorocarbon chains (Ar-SR-C8F17) showed the greatest reduction in microbial adhesion, probably because of their low surface free energy combined with a higher surface mobility. (C) 1998 Elsevier Science B.V.

Indwelling voice prostheses are most often made of silicone rubber. However, the silicone rubber surface attracts huge quantities of adhering yeasts and bacteria and their colonization on the valve side of voice prostheses leads to frequent malfunctioning. On average, indwelling voice prostheses have to be replaced every three to four months. In this paper, we report on the in vitro adhesion of yeasts and bacteria to fluoro-alkylsiloxane layers chemisorbed on silicone rubber surfaces, as measured in a parallel plate flow chamber. Silicone rubber surfaces were first oxidized with an argon plasma treatment (Ar-SR). In a second step, organic layers were created by chemisorption of fluoroalkyltrichlorosilanes onto the Ar-SR surfaces, denoted as Ar-SR-CF3 and Ar-SR-C8F17, respectively. Physico-chemical properties of the chemisorbed layers were studied by using water contact angle measurements, X-ray photoelectron spectroscopy (XPS) and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). Using a parallel plate flow chamber, adhesion of Streptococcus salivarius, Staphylococcus epidermidis, Candida albicans and Candida tropicalis strains, isolated from explanted voice prostheses, was investigated to the chemisorbed fluoroalkylsiloxane layers with and without a salivary conditioning film. Ar-SR-CF3 and Ar-SR-C8F17 surfaces showed significantly reduced microbial adhesion as compared to original silicone rubber, both with respect to initial deposition rates and adhesion in a stationary end-point. Furthermore, adhering microorganisms were more easily detached when applying an air-liquid interface. Silicone rubber surfaces with chemisorbed, long fluorocarbon chains (Ar-SR-C8F17) showed the greatest reduction in microbial adhesion, probably because of their low surface free energy combined with a higher surface mobility. (C) 1998 Elsevier Science B.V.

Microbial adhesion to hydrocarbons (MATH) is generally considered to be a measure of the organisms cell surface hydrophobicity. Recent observations that the zeta potentials of hydrocarbons can be highly negative in the various solutions commonly used in MATH, have suggested that MATH may measure a complicated interplay of long-range van der Waals and electrostatic forces and of various short-range interactions. By carrying out the MATH test on two intrinsically hydrophobic (i.e. by water contact angle) and two intrinsically hydrophilic microbial strains, it was demonstrated that the hydrophobic strains were removed by the hydrocarbons in a pH dependent fashion, with maximal removal at pH values where the zeta potentials of the organisms and/or of the hydrocarbons are zero, that is in the absence of electrostatic repulsion. The hydrophilic strains were not removed by the hydrocarbons to any significant extent, because the attractive forces between water and the organisms are much stronger than those between the organisms and the hydrocarbon droplets, in line with the low water contact angles on these microorganisms. These observations clearly disqualify MATH as a hydrophobicity assay. Possibly, the maximal initial removal rates for microorganisms by a given hydrocarbon at pH values where electrostatic repulsion is absent, can be considered as a measure for microbial cell surface hydrophobicity.

Microbial adhesion to hydrocarbons (MATH) is generally considered to be a measure of the organisms cell surface hydrophobicity. As microbial adhesion is a complicated interplay of long-range van der Waals and electrostatic forces and various short-range interactions, the above statement only holds when the MATH lest is carried out under conditions where the interacting surfaces are uncharged. In the present study it is shown that the most commonly used hydrocarbons in MATH, aliphatic octane and hexadecane, and aromatic xylene and toluene, are highly negatively charged in solutions in which MATH is often carried out. Zeta potentials of the aliphatic hydrocarbon droplets were generally more negative than those of the aromatic hydrocarbons with values as negative as up to -60 mV at pH 7, but hovered around zero at acidic pH values for both types of hydrocarbons. For the aromatic hydrocarbons, zeta potentials hovered around zero up to pH 4-5, but for the aliphatic hydrocarbons, most notably octane, zeta potentials decreased sharply starting at pH 2-3. The different pH dependence of the zeta potentials of the aliphatic hydrocarbons as compared to those of the aromatic hydrocarbons is most likely due to the hydrogen-accepting capacity of the electron ring in the aromatic hydrocarbons and can have major implications for the adhesion of microorganisms to these hydrophobic surfaces in MATH.

Microbial adhesion to hydrocarbons (MATH) is generally considered to be a measure of the organisms cell surface hydrophobicity. Recent observations that the zeta potentials of hydrocarbons can be highly negative in the various solutions commonly used in MATH, have suggested that MATH may measure a complicated interplay of long-range van der Waals and electrostatic forces and of various short-range interactions. By carrying out the MATH test on two intrinsically hydrophobic (i.e. by water contact angle) and two intrinsically hydrophilic microbial strains, it was demonstrated that the hydrophobic strains were removed by the hydrocarbons in a pH dependent fashion, with maximal removal at pH values where the zeta potentials of the organisms and/or of the hydrocarbons are zero, that is in the absence of electrostatic repulsion. The hydrophilic strains were not removed by the hydrocarbons to any significant extent, because the attractive forces between water and the organisms are much stronger than those between the organisms and the hydrocarbon droplets, in line with the low water contact angles on these microorganisms. These observations clearly disqualify MATH as a hydrophobicity assay. Possibly, the maximal initial removal rates for microorganisms by a given hydrocarbon at pH values where electrostatic repulsion is absent, can be considered as a measure for microbial cell surface hydrophobicity.

Microbial adhesion to hydrocarbons (MATH) is generally considered to be a measure of the organisms cell surface hydrophobicity. As microbial adhesion is a complicated interplay of long-range van der Waals and electrostatic forces and various short-range interactions, the above statement only holds when the MATH lest is carried out under conditions where the interacting surfaces are uncharged. In the present study it is shown that the most commonly used hydrocarbons in MATH, aliphatic octane and hexadecane, and aromatic xylene and toluene, are highly negatively charged in solutions in which MATH is often carried out. Zeta potentials of the aliphatic hydrocarbon droplets were generally more negative than those of the aromatic hydrocarbons with values as negative as up to -60 mV at pH 7, but hovered around zero at acidic pH values for both types of hydrocarbons. For the aromatic hydrocarbons, zeta potentials hovered around zero up to pH 4-5, but for the aliphatic hydrocarbons, most notably octane, zeta potentials decreased sharply starting at pH 2-3. The different pH dependence of the zeta potentials of the aliphatic hydrocarbons as compared to those of the aromatic hydrocarbons is most likely due to the hydrogen-accepting capacity of the electron ring in the aromatic hydrocarbons and can have major implications for the adhesion of microorganisms to these hydrophobic surfaces in MATH.

Microbial adhesion to hydrocarbons (MATH) is generally considered to be a measure of the organisms cell surface hydrophobicity. Recent observations that the zeta potentials of hydrocarbons can be highly negative in the various solutions commonly used in MATH, have suggested that MATH may measure a complicated interplay of long-range van der Waals and electrostatic forces and of various short-range interactions. By carrying out the MATH test on two intrinsically hydrophobic (i.e. by water contact angle) and two intrinsically hydrophilic microbial strains, it was demonstrated that the hydrophobic strains were removed by the hydrocarbons in a pH dependent fashion, with maximal removal at pH values where the zeta potentials of the organisms and/or of the hydrocarbons are zero, that is in the absence of electrostatic repulsion. The hydrophilic strains were not removed by the hydrocarbons to any significant extent, because the attractive forces between water and the organisms are much stronger than those between the organisms and the hydrocarbon droplets, in line with the low water contact angles on these microorganisms. These observations clearly disqualify MATH as a hydrophobicity assay. Possibly, the maximal initial removal rates for microorganisms by a given hydrocarbon at pH values where electrostatic repulsion is absent, can be considered as a measure for microbial cell surface hydrophobicity.

Microbial adhesion to hydrocarbons (MATH) is generally considered to be a measure of the organisms cell surface hydrophobicity. As microbial adhesion is a complicated interplay of long-range van der Waals and electrostatic forces and various short-range interactions, the above statement only holds when the MATH test is carried out under conditions where the interacting surfaces are uncharged. In the present study it is shown that the most commonly used hydrocarbons in MATH, aliphatic octane and hexadecane, and aromatic xylene and toluene, are highly negatively charged in solutions in which MATH is often carried out. Zeta potentials of the aliphatic hydrocarbon droplets were generally more negative than those of the aromatic hydrocarbons with values as negative as up to −60 mV at pH 7, but hovered around zero at acidic pH values for both types of hydrocarbons. For the aromatic hydrocarbons, zeta potentials hovered around zero up to pH 4–5, but for the aliphatic hydrocarbons, most notably octane, zeta potentials decreased sharply starting at pH 2–3. The different pH dependence of the zeta potentials of the aliphatic hydrocarbons as compared to those of the aromatic hydrocarbons is most likely due to the hydrogen-accepting capacity of the electron ring in the aromatic hydrocarbons and can have major implications for the adhesion of microorganisms to these hydrophobic surfaces in MATH.

Deposition of the oral bacterium Streptococcus sobrinus HG977 onto glass (water contact angle 0 degrees) and onto FEP-Teflon (fluoroethylenepropylene; water contact angle 110 degrees)was studied in a parallel-plate flow chamber in the presence and absence of polyclonal antibodies (pAb) and monoclonal antibodies (mAbs) adsorbed onto the cells. The zeta potentials of the bacteria ranged from -7.1 to -8.5 mV at pH 6.8 and were not affected by the presence of pAb or mAbs. Hydrophobicity (by water contact angles) increased from 30 degrees (no antibodies) to 88 degrees in the presence of pAb adsorbed onto the bacterial cell surface. The untreated S. sobrinus had a greater tendency to adhere to glass (44.5 x 10(6) cm(-2)) than to FEP-Teflon (18.3 x 10(6) cm(-2)), in accordance with thermodynamic modelling. After preincubation of S. sobrinus with pAb, its clear preference for adhesion to glass disappeared as expected from its increased hydrophobicity. Although for S. sobrinus preincubated with OMVU10 no difference was found in hydrophobicity in comparison to the untreated bacteria, the number of bacteria adhering to glass decreased to 10.2 x 10(6) cm(-2) Formation of bacterial aggregates was found when S. sobrinus, preincubated with pAb or OMVU10, adhered to glass and FEP. This was also observed when untreated bacteria adhered to glass coated with OMVU10, or to FEP coated with OMVU10 or pAb. Adhesion in these experiments is therefore thought to occur via near-neighbour collection induced by the presence of pAb or mAbs. Low numbers of bacteria were removed from glass after draining the flow cell, whereas high numbers of untreated bacteria and bacteria preincubated with OMVU10 were removed from FEP. S. sobrinus cells preincubated with pAb were not removed but piled up. It was concluded that the adhesion of untreated S. sobrinus and S. sobrinus preincubated with pAb is in accordance with thermodynamic modelling, based on the overall wettability of the cell surfaces, whereas the adhesion of S. sobrinus preincubated with OMVU10 may be through localized interactions, not expressed in overall surface properties.

Deposition of the oral bacterium Streptococcus sobrinus HG977 onto glass (water contact angle 0 degrees) and onto FEP-Teflon (fluoroethylenepropylene; water contact angle 110 degrees)was studied in a parallel-plate flow chamber in the presence and absence of polyclonal antibodies (pAb) and monoclonal antibodies (mAbs) adsorbed onto the cells. The zeta potentials of the bacteria ranged from -7.1 to -8.5 mV at pH 6.8 and were not affected by the presence of pAb or mAbs. Hydrophobicity (by water contact angles) increased from 30 degrees (no antibodies) to 88 degrees in the presence of pAb adsorbed onto the bacterial cell surface. The untreated S. sobrinus had a greater tendency to adhere to glass (44.5 x 10(6) cm(-2)) than to FEP-Teflon (18.3 x 10(6) cm(-2)), in accordance with thermodynamic modelling. After preincubation of S. sobrinus with pAb, its clear preference for adhesion to glass disappeared as expected from its increased hydrophobicity. Although for S. sobrinus preincubated with OMVU10 no difference was found in hydrophobicity in comparison to the untreated bacteria, the number of bacteria adhering to glass decreased to 10.2 x 10(6) cm(-2) Formation of bacterial aggregates was found when S. sobrinus, preincubated with pAb or OMVU10, adhered to glass and FEP. This was also observed when untreated bacteria adhered to glass coated with OMVU10, or to FEP coated with OMVU10 or pAb. Adhesion in these experiments is therefore thought to occur via near-neighbour collection induced by the presence of pAb or mAbs. Low numbers of bacteria were removed from glass after draining the flow cell, whereas high numbers of untreated bacteria and bacteria preincubated with OMVU10 were removed from FEP. S. sobrinus cells preincubated with pAb were not removed but piled up. It was concluded that the adhesion of untreated S. sobrinus and S. sobrinus preincubated with pAb is in accordance with thermodynamic modelling, based on the overall wettability of the cell surfaces, whereas the adhesion of S. sobrinus preincubated with OMVU10 may be through localized interactions, not expressed in overall surface properties.

Alternatives for less and less effective antibiotic treatment of bacterial infections, are amongst others based on nanotechnological innovations, like carbon-dots. However, with a focus on chemistry, important characteristics of bacterial strains, like (in-)ability to produce extracellular-polymeric-substances (EPS) are often neglected. EPS is the glue that certain bacterial strains produce to keep a biofilm together. Here we report on synthesis of novel, pH-responsive, 2,3-dimethylmaleic-anhydride modified carbon-dots (C-DMMA-dots). C-DMMA-dots, like unmodified C-dots without DMMA, were little bactericidal. However, C-DMMA-dots reduced volumetric-bacterial-density within the acidic-environment of a biofilm for a non-EPS-producing Staphylococcus epidermidis strain, indicative for a more open structure. Such a structural disruption was not observed for an EPS-producing strain. Disrupted biofilms of the non-EPS-producing strain pre-exposed to C-DMMA-dots at pH 5.0, were more amenable to vancomycin penetration and killing of their inhabitants than biofilms of EPS-producing-staphylococci. Herewith, we describe a new role of carbon-dots as synthetic disruptants of biofilm structure. It is a partial success story, identifying the challenge of making carbon-dots that act as a universal disruptant for biofilms of strains with different microbiological characteristics, most notably the ability to produce or not-produce EPS. Such carbon-dots, will enable more effective clinical treatment of bacterial infections combined with current antibiotics.