Surface properties and bacterial adhesion on polyurethane central catheters: Impact of ethanol lock solution.

It was shown in the literature that ethanol locks have a positive effect on preventing catheter-related infections in patients with central venous catheters without causing any microbial resistance. However, ethanol is known to interact with polyurethanes. The consequences of this interaction on the catheter surface properties were studied as it can impact the biocompatibility of the material and the adhesion phenomena onto the surface. No physical and chemical degradation was put into evidence, but low molecular weight compounds such as additives were extracted from the catheter bulk or migrated and exudated onto its surface. Nevertheless, as far as bacterial adhesion is concerned, after the catheter was locked and the lock removed, the surface modifications promoted no adhesion.

Possible overestimation of surface disinfection efficiency by assessment methods based on liquid sampling procedures as demonstrated by in situ quantification of spore viability.

The standard test methods used to assess the efficiency of a disinfectant applied to surfaces are often based on counting the microbial survivors sampled in a liquid, but total cell removal from surfaces is seldom achieved. One might therefore wonder whether evaluations of microbial survivors in liquid-sampled cells are representative of the levels of survivors in whole populations. The present study was thus designed to determine the "damaged/undamaged" status induced by a peracetic acid disinfection for Bacillus atrophaeus spores deposited on glass coupons directly on this substrate and to compare it to the status of spores collected in liquid by a sampling procedure. The method utilized to assess the viability of both surface-associated and liquid-sampled spores included fluorescence labeling with a combination of Syto 61 and Chemchrome V6 dyes and quantifications by analyzing the images acquired by confocal laser scanning microscopy. The principal result of the study was that the viability of spores sampled in the liquid was found to be poorer than that of surface-associated spores. For example, after 2 min of peracetic acid disinfection, less than 17% ± 5% of viable cells were detected among liquid-sampled cells compared to 79% ± 5% or 47% ± 4%, respectively, when the viability was evaluated on the surface after or without the sampling procedure. Moreover, assessments of the survivors collected in the liquid phase, evaluated using the microscopic method and standard plate counts, were well correlated. Evaluations based on the determination of survivors among the liquid-sampled cells can thus overestimate the efficiency of surface disinfection procedures.

The resistance of Bacillus atrophaeus spores to the bactericidal activity of peracetic acid is influenced by both the nature of the solid substrates and the mode of contamination.

AIMS: To evaluate the impact of the mode of contamination in relation with the nature of solid substrates on the resistance of spores of Bacillus atrophaeus -selected as surrogates of Bacillus anthracis- to a disinfectant, peracetic acid. METHODS AND RESULTS: Six materials confronted in urban and military environments were selected for their different structural and physicochemical properties. In parallel, two modes of contamination were examined, i.e. deposition and immersion. Deposition was used to simulate contamination by an aerosol and immersion by an extended contact with liquids. A pronounced difference in the biocontamination levels and spatial organization of spores was observed depending on the mode of contamination and the nature of the solid substrate considered, with consequences on decontamination. Contamination by immersion led to lower efficiency of peracetic acid decontamination than contamination by deposition. Infiltration of spores into porous materials after immersion is one reason. In contrast, the deposition mode aggregates cells at the surface of materials, explaining the similar disinfecting behaviour of porous and nonporous substrates when considering this inoculation route. CONCLUSIONS: The inoculation route was shown to be as influential a parameter as material characteristics (porosity and wettability) for decontamination efficacy. SIGNIFICANCE AND IMPACT OF THE STUDY: These results provide comparative information for the decontamination of B. atrophaeus spores in function of the mode of contamination and the nature of solid substrates.

Microbial inactivation using plasma-activated water obtained by gliding electric discharges.

AIM: To evaluate the microbial disinfection efficacy of a plasmachemical solution obtained by the activation of water with gliding electric discharges. METHODS AND RESULTS: Distilled water was activated for 5 min by a nonthermal quenched plasma of the glidarc type operating in humid air and at atmospheric pressure. The plasma-activated water (PAW) was then used to treat planktonic and adherent cells of Staphylococcus epidermidis, Leuconostoc mesenteroides (as models of Gram-positive bacteria), Hafnia alvei (a Gram-negative bacteria) and Saccharomyces cerevisiae (as a yeast model). The treatments were less efficient on adherent cells than on planktonic cells in the case of bacteria, but not of S. cerevisiae. Inactivation was more effective for bacteria than for the yeast. CONCLUSIONS: Significant reductions in microbial populations were achieved in all cases, demonstrating the effectiveness of this new approach to treat contaminated media. SIGNIFICANCE AND IMPACT OF THE STUDY: PAW is a promising solution with potential application to the decontamination of equipment and surfaces.

Kinetic adhesion of bacterial cells to sand: cell surface properties and adhesion rate.

Correlation between microbial surface thermodynamics using the extended DLVO (XDLVO) theory and kinetic adhesion of various bacterial cells to sand was investigated. Two experimental setups were utilized. Adhesion tests were conducted in batch reactors with slow agitation. Also, bacteria were circulated through small sand columns in a closed loop and the results were analyzed with a simple model which accounted for the rate of the adhesion phenomena (omega in h(-1)) and adhesion percentage. Cells surface properties were derived from contact angle measurements. The wicking method was utilized to characterize the sand. Zeta potentials were measured for the sand and the cells. Kinetic of bacterial retention by the porous media was largely influenced by the electrostatic interactions which are correlated with omega from the model (R(2)=0.71). Negative zeta potentials resulted in electrostatic repulsions occurring between the sand and the bacterial cells which in result delayed bacterial adhesion. While no correlation was found between the adhesion percentage and the total interaction energy calculated with the XDLVO theory the respective behavior of hydrophobic and hydrophilic bacteria as well as the importance of electrostatic interactions was evidenced. All the bacterial strains studied adhered more in the column experiments than in the adhesion tests, presumably due to enhanced collision efficiency and wedging in porous media, while filtration could be ignored except for the larger Bacillus strains. Approximate XDLVO calculations due to solid surface nanoscale roughness, retention in a secondary minimum and population heterogeneity are discussed. Our results obtained with a large variety of different physicochemical bacterial strains highlights the influence of both surface thermodynamics and porous media related effects as well as the limits of using the XDLVO theory for evaluating bacterial retention through porous media.

Characterization of the surface physico-chemistry of plasticized PVC used in blood bag and infusion tubing.

Commercial infusion tubing and blood storage devices (tubing, blood and platelets bags) made of plasticized PVC were analyzed by spectroscopic, chromatographic and microscopic techniques in order to identify and quantify the additives added to the polymer (lubricants, thermal stabilizers, plasticizers) and to put into evidence their blooming onto the surface of the devices. For all the samples, deposits were observed on the surface but with different kinds of morphologies. Ethylene bis amide lubricant and metallic stearate stabilizers were implicated in the formation of these layers. In contact with aqueous media, these insoluble deposits were damaged, suggesting a possible particulate contamination of the infused solutions.

Alteration of bacterial adhesion induced by the substrate stiffness.

The aim of this paper is to study the impact of the substrate stiffness on the bacterial adhesion. For this purpose, agarose hydrogels are used as substrates with controlled mechanical properties. Indeed, the elastic modulus of these hydrogels, more precisely the shear storage moduli G', evolves with the agarose concentration (in this study from 0.75% to 3%). Other physico-chemical characteristics of the surface, known to be involved in bacterial adhesion, as hydrophobicity, were confirmed to remain constant. Two marine bacterial strains, a positive Gram Bacillus sp. 4J6 and a negative Gram Pseudoalteromonas sp. D41 were selected. Their retention on the substrates was analysed by confocal laser scanning microscopy and by counting of viable adhered bacteria. It was demonstrated that surface elastic modulus correlated with bacterial retention. Bacteria D41 adhered in higher numbers to rigid surfaces. For 4J6, bacterial adhesion patterns were changed: clusterings were observed on surfaces with lower elastic modulus. Furthermore, a proteomic study, based on the total soluble proteome of D41 strain, highlights an impact of elastic modulus on proteins synthesis. These data demonstrated an adapted response of adhering bacteria on hydrogels of varying mechanical properties.

Elaboration of highly hydrophobic polymeric surface--a potential strategy to reduce the adhesion of pathogenic bacteria?

Different polymeric surfaces have been modified in order to reach a high hydrophobic character, indeed the superhydrophobicity property. For this purpose, polypropylene and polystyrene have been treated by RF or µwaves CF4 plasma with different volumes, the results were compared according to the density of injected power. The effect of pretreatment such as mechanical abrasion or plasma activation was also studied. The modified surfaces were shown as hydrophobic, or even superhydrophobic depending of defects density. They were characterized by measurement of wettability and roughness at different scales, i.e. macroscopic, mesoscopic and atomic. It has been shown that a homogeneous surface at the macroscopic scale could be heterogeneous at lower mesoscopic scale. This was associated with the crystallinity of the material. The bioadhesion tests were performed with Gram positive and negative pathogenic strains: Listeria monocytogenes, Pseudomonas aeruginosa and Hafnia alvei. They have demonstrated an antibacterial efficiency of very hydrophobic and amorphous PS treated for all strains tested and a strain-dependent efficiency with modified PP surface being very heterogeneous at the mesoscopic scale. Thus, these biological results pointed out not only the respective role of the surface chemistry and topography in bacterial adhesion, but also the dependence on the peaks and valley distribution at bacteria dimension scale.

Destruction of planktonic, adherent and biofilm cells of Staphylococcus epidermidis using a gliding discharge in humid air.

AIMS: To determine the efficiency of an electric discharge of the gliding arc type for the destruction of Staphylococcus epidermidis planktonic, adherent and biofilm cells. METHODS AND RESULTS: Bacterial cells were treated in humid air and at atmospheric pressure by a nonthermal quenched plasma of the glidarc type. The kinetics of destruction (followed by plating) were modelled by an Add-inn for Microsoft Excel, GInaFiT. For planktonic cells, log-linear destruction was obtained, whereas biphasic kinetics were observed for sessile cells. An increased resistance of biofilm cells was observed: the reduction of 6 logarithm units of the population was obtained in 15, 30 and 70 min for planktonic, adherent and biofilm cells, respectively. The experiments also show that the cells destruction did not depend on the adhesion surface but was governed by the gap between the target and the plasma source. CONCLUSION: The complete destruction of planktonic, adherent and more resistant biofilm cells of Staph. epidermidis is achieved by a glidarc air plasma at atmospheric pressure. SIGNIFICANCE AND IMPACT OF THE STUDY: The glidarc plasma technology is a promising candidate among the emerging nonthermal techniques for decontamination, as it can destroy even biofilms that are known as particularly resistant to various antimicrobials.

Elimination of adhering bacteria from surfaces by pulsed laser beams.

As an alternative to the use of chemicals for cleaning and disinfecting surfaces of equipment in food industry, the efficacy of pulsed laser beams for removal and killing of adherent bacteria from stainless steel surfaces was assessed. Escherichia coli biofilms were produced under dynamic conditions in diluted nutritive medium incubated at 37 degrees C for 24 h. Influence of energy density and number of shots were tested at three wavelengths (1064, 532 and 355 nm). With one 20 ns pulse, results range from 3.5 decimal reductions of the microbial load with < or = 50 MW cm-2 without visible alteration of the surface, to more than 6 decimal reductions with < or = 600 MW cm-2. The measured effect was largely attributed to removal of the micro-organisms and transfer to the surrounding air. The treatment could therefore be improved with respect to the numbers remaining associated with the surface by venting.

Determination of the van der Waals, electron donor and electron acceptor surface tension components of static Gram-positive microbial biofilms.

A large number of studies have shown the influence of the physico-chemical properties of a surface on microbial adhesion phenomenon. In this study, we considered that the presence of a bacterial biofilm may be regarded as a "conditioning film" that may modify the physico-chemical characteristics of the support, and thus the adhesion capability of planktonic micro-organisms coming into contact with this substratum. In this context, we adapted a protocol for biofilm formation that allows, under our experimental conditions, contact angle measurements, the reference method to determine the energetic surface properties of a substratum. This made it possible to determine the van der Waals, electron acceptor and electron donor properties of static biofilms grown at 25 degrees C on stainless-steel slides with six Gram-positive bacteria isolated in dairy plants. A variance analysis indicated significant effects (P<0.05) of the bacterial strains and of the physiological state of the micro-organisms (planktonic or sessile) on the contact angles. To link the energetic properties of the six biofilms with direct adhesion experiments, we measured the affinity of fluorescent carboxylate-modified polystyrene beads for the different biofilm surfaces. The results correlated best with the electron-acceptor components of the biofilm surface energies, stressing the importance of Lewis acid-base interactions in adhesion mechanisms.