Marie-Noëlle Bellon-Fontaine

Microbial adhesion to solvents: a novel method to determine the electron-donor/electron-acceptor or Lewis acid-base properties of microbial cells

Abstract Lewis acid-base, i.e. electron-donor/electron-acceptor, interactions are implicated in various interffacial phenomena such as phagocytosis, biofouling and microbial adhesion. Therefore, the determination of electron-donor/electron-acceptor properties of microbial cells can be of importance in many research areas. However, until now, there has only been one method to determine these properties which is based on contact angle measurements combined with the equations of van Oss. Consequently, this method requires specific and elaborate equipment. Thus to facilitate the characterization of microbial cell surfaces, we have developed a simple, rapid and quantitative technique, the MATS (microbial adhesion to solvents) method, which is based on the comparison between microbial cell affinity to a monopolar solvent and a polar solvent. The monopolar solvent can be acidic (electron acceptor) or basic (electron donor) but both solvents must have similar surface tension Lifshitz-van der Waals components. Using this new method we have shown that Streptococcus thermophilus B (STB) and Leuconostoc mesenteroides NCDO 523 (LM 523) display maximal affinity for an acidic solvent and a low affinity for basic solvents. There was not a great difference between microbial cell adherence to basic solvents and apolar solvents, except for STB suspended in a 0.1 mol l −1 potassium phosphate buffer. These results, which demonstrate that both bacteria are strong electron donors and very weak electron acceptors, are in accordance with the energetic characteristics derived from van Osss approach.

Listeria monocytogenes LO28: Surface Physicochemical Properties and Ability To Form Biofilms at Different Temperatures and Growth Phases

ABSTRACT The surface physicochemical properties of Listeria monocytogenes LO28 under different conditions (temperature and growth phase) were determined by use of microelectrophoresis and microbial adhesion to solvents. The effect of these parameters on adhesion and biofilm formation by L. monocytogenes LO28 on hydrophilic (stainless steel) and hydrophobic (polytetrafluoroethylene [PTFE]) surfaces was assessed. The bacterial cells were always negatively charged and possessed hydrophilic surface properties, which were negatively correlated with growth temperature. The colonization of the two surfaces, monitored by scanning electron microscopy, epifluorescence microscopy, and cell enumeration, showed that the strain had a great capacity to colonize both surfaces whatever the incubation temperature. However, biofilm formation was faster on the hydrophilic substratum. After 5 days at 37 or 20°C, the biofilm structure was composed of aggregates with a three-dimensional shape, but significant detachment took place on PTFE at 37°C. At 8°C, only a bacterial monolayer was visible on stainless steel, while no growth was observed on PTFE. The growth phase of bacteria used to inoculate surfaces had a significant effect only in some cases during the first steps of biofilm formation. The surface physicochemical properties of the strain are correlated with adhesion and surface colonization.

Combined Effects of Long-Living Chemical Species during Microbial Inactivation Using Atmospheric Plasma-Treated Water

ABSTRACT Electrical discharges in humid air at atmospheric pressure (nonthermal quenched plasma) generate long-lived chemical species in water that are efficient for microbial decontamination. The major role of nitrites was evidenced together with a synergistic effect of nitrates and H2O2 and matching acidification. Other possible active compounds are considered, e.g., peroxynitrous acid.

Adsorption of biosurfactant on solid surfaces and consequences regarding the bioadhesion of Listeria monocytogenes LO28

Aims: The influence of biosurfactant compounds produced by a strain of Pseudomonas fluorescens on the adhesion of Listeria monocytogenes LO28 to polytetrafluoroethylene (PTFE) and AISI 304 stainless steel surfaces was investigated.

Fluorescence correlation spectroscopy to study diffusion and reaction of bacteriophages inside biofilms.

ABSTRACT In the natural environment, most of the phages that target bacteria are thought to exist in biofilm ecosystems. The purpose of this study was to gain a clearer understanding of the reactivity of these viral particles when they come into contact with bacteria embedded in biofilms. Experimentally, we quantified lactococcal c2 phage diffusion and reaction through model biofilms using in situ fluorescence correlation spectroscopy with two-photon excitation. Correlation curves for fluorescently labeled c2 phage in nonreacting Stenotrophomonas maltophilia biofilms indicated that extracellular polymeric substances did not provide significant resistance to phage penetration and diffusion, even though penetration and diffusion were sometimes restricted because of the noncontractile tail of the viral particle. Fluctuations in the fluorescence intensity of the labeled phage were detected throughout the thickness of biofilms formed by c2-sensitive and c2-resistant strains of Lactococcus lactis but could never be correlated with time, revealing that the phage was immobile. This finding confirmed that recognition binding receptors for the viral particles were present on the resistant bacterial cell wall. Taken together, our results suggest that biofilms may act as “active” phage reservoirs that can entrap and amplify viral particles and protect them from harsh environments.

Effects of the Growth Procedure on the Surface Hydrophobicity of Listeria monocytogenes Cells and Their Adhesion to Stainless Steel

The aim of this study was to examine the physicochemical surface properties and the ability to adhere to stainless steel of three strains of Listeria monocytogenes after different cultivation procedures. To this end, bacteria were cultivated at 37 degrees C after storage at two frequently used temperatures (4 degrees C or -80 degrees C) and were then transferred into the liquid medium (trypticase soy broth supplemented with 6 g liter(-1) of yeast extract, pH 7.3) between one and four times. In addition, the influence of supplementing the growth medium with lactic acid was explored, this organic acid being representative of both the dairy and cured meat industries. The hydrophobic/hydrophilic and electron-acceptor/electron-donor characteristics of the strains were evaluated by the microbial adhesion to solvents method. Using this technique, we recorded an increase in the hydrophobic properties of one strain stored at 4 degrees C, with an increasing number of transfers in the media (P < 0.05). Another plant-isolated strain appeared more hydrophobic and stuck better to stainless steel when cells were stored at 4 degrees C rather than at -80 degrees C. Preculturing L. monocytogenes in a lactic acid-supplemented medium increased the affinity of microbial cells to solvents and the bacterial attachment to stainless steel (P < 0.05).

Kinetics of conditioning layer formation on stainless steel immersed in seawater

Adhesion of microorganisms to surfaces in marine environments leads to biofouling. The deleterious effects of biofilm growth in the marine environment are numerous and include energy losses due to increased fluid frictional resistance or to increased heat transfer resistance, the risk of corrosion induced by microorganisms, loss of optical properties, and quality control and safety problems. Antifouling agents are generally used to protect surfaces from such a biofilm. These agents are toxic and can be persistent, causing harmful environmental and ecological effects. Moreover, the use of biocides and regular cleaning considerably increase the maintenance costs of marine industries. An improved knowledge of bio‐film adhesion mechanisms is needed for the development of an alternative approach to the currently used antifouling agents. The aim of this study is to characterise the chemical composition of the molecules first interacting with stainless steel during the period immediately following immersion in natural seawater and to elucidate the kinetics of the adsorbtion process. Proteins are shown to adhere very rapidly, closely followed by carbohydrates. The distribution on the surface of organic molecules is also examined. The ad‐sorbate on the surface is not a continuous film but a heterogeneous deposit, whose average thickness varies widely. The cleaning procedures used affect the adsorption kinetics. In particular, cleaning with hexane results in slower adsorption of nitrogen‐containing species than does cleaning in acetone.

Adhesion of streptococcus thermophilus to stainless steel with different surface topography and roughness

Adhesion of Streptococcus thermophilus to AISI 304 stainless steel was studied with regard to surface topography and roughness and surface hydrophobicity. Different finishes of stainless steel were used, viz. industrial surfaces 2R and 2B and polished surfaces 3, 5 and 8. A surface tracing instrument with low resolution was not the most suitable technique to characterise solid surfaces for bacterial adhesion studies. Surface roughnesses measurements varied from 0.01 to 1 μm. The surfaces were hydrophobic initially. The number of bacteria (N) adhering to the stainless steel surfaces did not vary significantly (log N varied from 5.2 to 5.7). Three cycles of bacterial adhesion followed by a cleaning treatment were applied to the different stainless finishes. After the third cycle, bacterial clumping was observed on stainless steel surfaces. The reasons for this observation are discussed.

The influence of metallic surface wettability on bacterial adhesion

The wettability of AISI 304 stainless steel with 2B and 2RB surface finishes expressed in terms of the solid surface free energy was investigated with respect to the cleaning process. It was shown that cleaning affects the wettability of a solid surface. Depending on the cleaning method, ranged from 43.4 to 277.8 mJ m-2 for the 2RB surface and from 34.4 to 122.8 mJ m 2 for the 2B surface. There was no direct relationship between the number of adhering bacteria and or the wettability of solids. However, it was found that the adhesion of Streptococcus thermophilus was driven by a balance between and The experimental results are as expected based on thermodynamic predictions when the spreading pressure is accounted for in the surface free energy of bacteria, determination.

Evidence of Temporal Postdischarge Decontamination of Bacteria by Gliding Electric Discharges: Application to Hafnia alvei

ABSTRACT This study aimed to characterize the bacterium-destroying properties of a gliding arc plasma device during electric discharges and also under temporal postdischarge conditions (i.e., when the discharge was switched off). This phenomenon was reported for the first time in the literature in the case of the plasma destruction of microorganisms. When cells of a model bacterium, Hafnia alvei, were exposed to electric discharges, followed or not followed by temporal postdischarges, the survival curves exhibited a shoulder and then log-linear decay. These destruction kinetics were modeled using GinaFiT, a freeware tool to assess microbial survival curves, and adjustment parameters were determined. The efficiency of postdischarge treatments was clearly affected by the discharge time (t*); both the shoulder length and the inactivation rate kmax were linearly modified as a function of t*. Nevertheless, all conditions tested (t* ranging from 2 to 5 min) made it possible to achieve an abatement of at least 7 decimal logarithm units. Postdischarge treatment was also efficient against bacteria not subjected to direct discharge, and the disinfecting properties of “plasma-activated water” were dependent on the treatment time for the solution. Water treated with plasma for 2 min achieved a 3.7-decimal-logarithm-unit reduction in 20 min after application to cells, and abatement greater than 7 decimal logarithm units resulted from the same contact time with water activated with plasma for 10 min. These disinfecting properties were maintained during storage of activated water for 30 min. After that, they declined as the storage time increased.