H.C. van der Mei

Bacterial adhesion to surface hydrophilic and hydrophobic contact lenses

The aim of this paper was to determine the adhesion of two physico-chemically characterized bacterial strains to a surface hydrophilic (CL A, water contact angle 57 degrees) and hydrophobic (CL B, water contact angle 106 degrees) hydrogel contact lens (CL) with and without an adsorbed tear film in a parallel plate flow chamber. Hydrophobicity (by water contact angles), charge (by particulate microelectrophoresis) and elemental composition (by XPS) of the surfaces of seven bacterial strains were characterized, after which two strains were selected for further studies. On CL surfaces, hydrophobicity, elemental composition, and mean surface roughness (by AFM) were determined, as well as the protein composition of tear films adsorbed on these lenses (by sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE)). Bacterial cell surfaces were relatively uncharged and water contact angles on lawns of different strains ranged from hydrophobic to hydrophilic. After adsorption of tear film components, N/C elemental surface concentrations increased on CL A and CL B and differences in water contact angles between both lenses reduced to range from 57 degrees (CL A) to 69 degrees (CL B). However, different protein compositions were inferred. The surface roughness of CL A increased from 4 to 13 nm. while it remained 16 nm for CL B. Adhesion of hydrophobic Pseudomonas aeruginosa #3 was more extensive than of hydrophilic Staphylococcus aureus 799, with no differences between both lenses. The hydrophobicity of P. aeruginosa #3 after cell surface damage decreased and its adhesion was reduced on CL A and strongly on CL B. In addition, passage of an air-liquid interface yielded more detachment of S. aureus 799 than of P. aeruginosa #3 from the CL surfaces. In conclusion, the hydrophobicity of CL surfaces dictates the composition of the adsorbed tear film and therewith plays an important role in bacterial adhesion to lenses. Adhesion of hydrophobic P. aeruginosa #3 was more tenacious than of hydrophilic S. aureus 799.

An in vivo Study of the Influence of the Surface Roughness of Implants on the Microbiology of Supra- and Subgingival Plaque

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

Backgrounds of antibiotic-loaded bone cement and prosthesis-related infection.

Antibiotic-loaded bone cement has been in use for over 30 years for the fixation of total joint arthroplasties, although its mechanism of action is still poorly understood. This review presents the backgrounds of bone cements, prosthesis-related infection and antibiotic-loaded bone cements. It is shown that antibiotic-loaded bone cement has a significant effect on bacteria, particularly in animal and clinical studies. However, recently, antimicrobial resistance among bacteria has been ascribed to the antibiotic-loaded bone cement. The unresolved issues both regarding the action of antibiotic-loaded bone cement and the nature of the antimicrobial resistance necessitate further research into the interaction of antibiotic-loaded bone cement and bacteria.

Detection of biomaterial associated infections in orthopaedic joint implants

Biomaterial-associated infection of orthopaedic joint replacements is the second most common cause of implant failure. Yet, the microbiologic detection rate of infection is relatively low, probably because routine hospital cultures are made only of swabs or small pieces of excised tissue and not of the surfaces of potentially infected implants. Joint replacements from patients in whom infection was suspected, after clinical, radiologic, and biochemical examinations, were used in this study. The aim of the current study was to compare the detection rate of infection in total joint replacements based on cultures of the excised tissue and scrapings from the biomaterial surface. Joint prostheses were retrieved from 22 patients requiring orthopaedic revision surgery because of suspected infection of their prostheses. Routine hospital culturing of tissue only showed bacterial growth in nine patients (41%). However, after prolonged culturing, bacterial growth was observed in 14 patients (64%), whereas extensive culturing of scrapings from the biomaterial surface indicated bacterial growth in 19 of the 22 patients (86%). In addition, confocal laser scanning microscopy enabled observation of biofilm bacteria on the surfaces of the explanted prostheses. Diagnosis in orthopaedic revision surgery should consider using a microbial or microscopic analysis of the surface of an explanted prosthesis, where the biofilm mode of growth firmly anchors and protects the infecting organisms. Improved detection of infection by analysis of the implant surface is expected to yield ameliorated therapy and a reduced need for revision surgery.

A reference guide to microbial cell surface hydrophobicity based on contact angles

Acid–base interactions form the origin of the hydrophobicity of microbial cell-surfaces and can be quantitated from contact angle measurements on microbial lawns with water, formamide, methyleneiodide and/or α-bromonaphthalene. This review provides a reference guide to microbial cell surface hydrophobicity based on contact angles with the above four diagnostic liquids and involves Acinetobacter calcoaceticus, Actinobacillus actinomycetemcomitans, actinomyces, Brevibacterium linens, various Candida species, Capnocytophaga gingivalis, Enterococci, Escherichia coli, lactobacilli, Leuconostoc mesenteroides, peptostreptococci, Porphyromonas gingivalis, Prevotella intermedia, pseudomonads, Serratia marcescens, staphylococci, and streptococci, adding up to a total of 142 isolates among which many ATCC and NCTC strains and two standard strains in hydrophobicity research. Comparison of the results of an acid-base analysis of the microbial cell surfaces on the basis of contact angles for the latter two strains and the results of the so-called MATH (microbial adhesion to hydrocarbons) assay for cell surface hydrophobicity, demonstrates that only contact angles can provide a real estimate of cell surface hydrophobicity. Furthermore, the compilation of contact angle data presented, makes clear that no generalizations concerning the physico-chemical surface properties of microorganisms may be made.

Biodeterioration of medical-grade silicone rubber used for voice prostheses: a SEM study

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

Pathogenesis and prevention of biomaterial centered infections

One of the major drawbacks in the use of biomedical materials is the occurrence of biomaterials centered infections. After implantation, the host interacts with a biomaterial by forming a conditioning film on its surface and an immune reaction towards the foreign material. When microorganisms can reach the biomaterials surface they can adhere to it. Adhesion of microorganisms to an implant is mediated by their physico-chemical surface properties and the properties of the biomaterials surface itself. Subsequent surface growth of the microorganisms will lead to a mature biofilm and infection, which is difficult to eradicate by antibiotics. The purpose of this review is to give an overview of the mechanisms involved in biomaterials centered infection and the possible methods to prevent these infections.

IMPLICATIONS OF MICROBIAL ADHESION TO HYDROCARBONS FOR EVALUATING CELL-SURFACE HYDROPHOBICITY .1. ZETA-POTENTIALS OF HYDROCARBON DROPLETS

Abstract 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.

IMPLICATIONS OF MICROBIAL ADHESION TO HYDROCARBONS FOR EVALUATING CELL-SURFACE HYDROPHOBICITY .2. ADHESION MECHANISMS

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.

Probing molecular interactions and mechanical properties of microbial cell surfaces by atomic force microscopy.

Knowledge of the surface properties of microbial cells is a key to gain a detailed understanding of their functions in the natural environment and to efficiently exploit them in biotechnological processes. In this paper, we present force-distance curves recorded, by atomic force microscopy (AFM) in aqueous solutions, on various microbial samples: reconstituted S-layers, whole fungal spores and several bacterial strains. The approach and retraction curves exhibited important differences--depending on the type of microorganism, on the physiological state (dormancy versus germination) and on the environmental conditions (ionic strength)--which were shown to reflect differences in long-range surface forces, adhesion forces and mechanical properties. These data illustrate the great potential of AFM force measurements to elucidate the physical properties of microbial cells and to understand, at the molecular level, biointerfacial phenomena such as cell adhesion and cell aggregation.