Exploring the hemicellulolytic properties and safety of Bacillus paralicheniformis as stepping stone in the use of new fibrolytic beneficial microbes

Bacillus strains from the Moroccan Coordinated Collections of Microorganisms (CCMM) were characterised and tested for fibrolytic function and safety properties that would be beneficial for maintaining intestinal homeostasis, and recommend beneficial microbes in the field of health promotion research. Forty strains were investigated for their fibrolytic activities towards complex purified polysaccharides and natural fibres representative of dietary fibres (DFs) entering the colon for digestion. We demonstrated hemicellulolytic activities for nine strains of Bacillus aerius, re-identified as Bacillus paralicheniformis and Bacillus licheniformis, using xylan, xyloglucan or lichenan as purified polysaccharides, and orange, apple and carrot natural fibres, with strain- and substrate-dependent production of glycoside hydrolases (GHs). Our combined methods, based on enzymatic assays, secretome, and genome analyses, highlighted the hemicellulolytic activities of B. paralicheniformis and the secretion of specific glycoside hydrolases, in particular xylanases, compared to B. licheniformis. Genomic features of these strains revealed a complete set of GH genes dedicated to the degradation of various polysaccharides from DFs, including cellulose, hemicellulose and pectin, which may confer on the strains the ability to digest a variety of DFs. Preliminary experiments on the safety and immunomodulatory properties of B. paralicheniformis fibrolytic strains were evaluated in light of applications as beneficial microbes' candidates for health improvement. B. paralicheniformis CCMM B969 was therefore proposed as a new fibrolytic beneficial microbe candidate.

Sperm-fluid-cell interplays in the bovine oviduct: glycosaminoglycans modulate sperm binding to the isthmic reservoir

When entering the oviduct for fertilisation, spermatozoa come into contact with the oviduct fluid (OF) and can bind to luminal epithelial cells in the isthmus to form a sperm reservoir. The objective of this study was to examine how the OF modulates sperm adhesion to the oviduct reservoir using an in vitro model of oviduct epithelial spheroids (OES). Bovine oviducts from a local slaughterhouse were used to collect OF and isthmic fragments for the in vitro incubation of OES. Compared to a non-capacitating control medium, the pre-ovulatory OF significantly decreased by 80-90% the density of spermatozoa bound to OES without affecting sperm motility, membrane integrity, or sperm-cilia interactions. This effect on sperm binding was reproduced with (1) OF from different cycle stages and anatomical regions of the oviduct; (2) OF fractions of more than 3 kDa; (3) modified OF in which proteins were denatured or digested and (4) heparan sulphate but not hyaluronic acid, two glycosaminoglycans present in the OF. In conclusion, the OF significantly decreased the number of spermatozoa that bind to oviduct epithelial cells without affecting sperm motility and this effect was due to macromolecules, including heparan sulphate.

Neonatal necrotizing enterocolitis: Clostridium butyricum and Clostridium neonatale fermentation metabolism and enteropathogenicity

Bacterial colonization in the gut plays a pivotal role in neonatal necrotizing enterocolitis (NEC) development, but the relationship between bacteria and NEC remains unclear. In this study, we aimed to elucidate whether bacterial butyrate end-fermentation metabolites participate in the development of NEC lesions and confirm the enteropathogenicity of Clostridium butyricum and Clostridium neonatale in NEC. First, we produced C.butyricum and C.neonatale strains impaired in butyrate production by genetically inactivating the hbd gene encoding β-hydroxybutyryl-CoA dehydrogenase that produces end-fermentation metabolites. Second, we evaluated the enteropathogenicty of the hbd-knockout strains in a gnotobiotic quail model of NEC. The analyses showed that animals harboring these strains had significantly fewer and less intense intestinal lesions than those harboring the respective wild-type strains. In the absence of specific biological markers of NEC, the data provide original and new mechanistic insights into the disease pathophysiology, a necessary step for developing potential novel therapies.

Freeze-dried fecal samples are biologically active after long-lasting storage and suited to fecal microbiota transplantation in a preclinical murine model of Clostridioides difficile infection

Fecal microbiota transplantation is now recommended for treating recurrent forms of Clostridioides difficile infection. Recent studies have reported protocols using capsules of either frozen or freeze-dried stool allowing oral administration in in- and out-patient settings. However, a central question remains the viability, engraftment, and efficacy of the microbiome over time during storage life. This study shows that both the freeze-drying and freezing procedures for fecal samples allowed preserving viability, short-chain fatty acids concentration, and anti-Clostridioides difficile properties of microbiota without significant alteration after storage for 12 months. Fecal transplantation with freeze-dried microbiota allowed engraftment of microbiota leading to clearance of Clostridioides difficile infection in a preclinical murine model with a survival rate of 70% versus 53-60% in mice treated with frozen inocula, and 20% in the untreated group. Moreover, the freeze-dried powder can be used to fill oral hard capsules using a very low amount (0.5%) of glidant excipient, allowing oral formulation. Altogether, this study showed that freeze-dried inocula can be used for the treatment of Clostridioides difficile infection with long-lasting stability of the fecal microbiota. This formulation facilitates biobanking and allows the use of hard capsules, an essential step to simplify patient access to treatment.

Identification of New Factors Modulating Adhesion Abilities of the Pioneer Commensal Bacterium Streptococcus salivarius

Biofilm formation is crucial for bacterial community development and host colonization by Streptococcus salivarius, a pioneer colonizer and commensal bacterium of the human gastrointestinal tract. This ability to form biofilms depends on bacterial adhesion to host surfaces, and on the intercellular aggregation contributing to biofilm cohesiveness. Many S. salivarius isolates auto-aggregate, an adhesion process mediated by cell surface proteins. To gain an insight into the genetic factors of S. salivarius that dictate host adhesion and biofilm formation, we developed a screening method, based on the differential sedimentation of bacteria in semi-liquid conditions according to their auto-aggregation capacity, which allowed us to identify twelve mutations affecting this auto-aggregation phenotype. Mutations targeted genes encoding (i) extracellular components, including the CshA surface-exposed protein, the extracellular BglB glucan-binding protein, the GtfE, GtfG and GtfH glycosyltransferases and enzymes responsible for synthesis of cell wall polysaccharides (CwpB, CwpK), (ii) proteins responsible for the extracellular localization of proteins, such as structural components of the accessory SecA2Y2 system (Asp1, Asp2, SecA2) and the SrtA sortase, and (iii) the LiaR transcriptional response regulator. These mutations also influenced biofilm architecture, revealing that similar cell-to-cell interactions govern assembly of auto-aggregates and biofilm formation. We found that BglB, CshA, GtfH and LiaR were specifically associated with bacterial auto-aggregation, whereas Asp1, Asp2, CwpB, CwpK, GtfE, GtfG, SecA2 and SrtA also contributed to adhesion to host cells and host-derived components, or to interactions with the human pathogen Fusobacterium nucleatum. Our study demonstrates that our screening method could also be used to identify genes implicated in the bacterial interactions of pathogens or probiotics, for which aggregation is either a virulence trait or an advantageous feature, respectively.

Forced- and Self-Rotation of Magnetic Nanorods Assembly at the Cell Membrane: A Biomagnetic Torsion Pendulum

In order to provide insight into how anisotropic nano-objects interact with living cell membranes, and possibly self-assemble, magnetic nanorods with an average size of around 100 nm × 1 µm are designed by assembling iron oxide nanocubes within a polymeric matrix under a magnetic field. The nano-bio interface at the cell membrane under the influence of a rotating magnetic field is then explored. A complex structuration of the nanorods intertwined with the membranes is observed. Unexpectedly, after a magnetic rotating stimulation, the resulting macrorods are able to rotate freely for multiple rotations, revealing the creation of a biomagnetic torsion pendulum.

Impact of temperature on Marinobacter hydrocarbonoclasticus SP17 morphology and biofilm structure during growth on alkanes

Alkanes are widespread pollutants found in soil, freshwater and marine environments. Marinobacter hydrocarbonoclasticus (Mh) strain SP17 is a marine bacterium able to use many hydrophobic organic compounds, including alkanes, through the production of biofilms that allow their poor solubility to be overcome. This study pointed out that temperature is an environmental factor that strongly affects the biofilm formation and morphology of Mh on the model alkanes, hexadecane and paraffin. We showed that Mh biofilm formation and accumulation of intracytoplasmic inclusions are higher on solid alkanes (hexadecane at 10 °C and paraffin at 10 °C and 30 °C) than on liquid alkane (hexadecane at 30 °C) or soluble substrate (lactate at both temperatures). We also found that Mh produces more extracellular polymeric substances at 30 °C than at 10 °C on alkanes and none on lactate. We observed that bacterial length is significantly higher at 10 °C than at 30 °C on lactate and hexadecane. On paraffin, at 30 °C, the cell morphology is markedly altered by large rounded or irregularly shaped cytoplasmic inclusions. Altogether, the results showed that Mh is able to adapt and use alkanes as a carbon source, even at low temperature.

Overexpression of Enterococcus faecalis elr operon protects from phagocytosis

Background

Mechanisms underlying the transition from commensalism to virulence in Enterococcus faecalis are not fully understood. We previously identified the enterococcal leucine-rich protein A (ElrA) as a virulence factor of E. faecalis. The elrA gene is part of an operon that comprises four other ORFs encoding putative surface proteins of unknown function.

Results

In this work, we compared the susceptibility to phagocytosis of three E. faecalis strains, including a wild-type (WT), a ΔelrA strain, and a strain overexpressing the whole elr operon in order to understand the role of this operon in E. faecalis virulence. While both WT and ΔelrA strains were efficiently phagocytized by RAW 264.7 mouse macrophages, the elr operon-overexpressing strain showed a decreased capability to be internalized by the phagocytic cells. Consistently, the strain overexpressing elr operon was less adherent to macrophages than the WT strain, suggesting that overexpression of the elr operon could confer E. faecalis with additional anti-adhesion properties. In addition, increased virulence of the elr operon-overexpressing strain was shown in a mouse peritonitis model.

Conclusions

Altogether, our results indicate that overexpression of the elr operon facilitates the E. faecalis escape from host immune defenses.

Electronic supplementary material

The online version of this article (doi:10.1186/s12866-015-0448-y) contains supplementary material, which is available to authorized users.

Plant-derived compounds as natural antimicrobials to control paper mill biofilms

Biofilms can cause severe problems in industrial paper mills, particularly of economic and technological types (clogging of filters, sheet breaks or holes in the paper, machine breakdowns, etc.). We present here some promising results on the use of essential oil compounds to control these biofilms. Biofilms were grown on stainless-steel coupons with a microbial white water consortium sampled from an industrial paper mill. Five essential oil compounds were screened initially in the laboratory in terms of their antimicrobial activity against planktonic cells and biofilms. The three most active compounds were selected and then tested in different combinations. The combination finally selected was tested at the pilot scale to confirm its efficiency under realistic conditions. All the compounds tested were as active against biofilms as they were against planktonic cells. The most active compounds were thymol, carvacrol, and eugenol, and the most efficient combination was thymol–carvacrol. At a pilot scale, with six injections a day, 10 mM carvacrol alone prevented biocontamination for at least 10 days, and a 1 mM thymol–carvacrol combination enabled a 67 % reduction in biofilm dry matter after 11 days. The use of green antimicrobials could constitute a very promising alternative or supplement to the treatments currently applied to limit biofilm formation in the environment of paper mill machines.

Enterococcus faecalis prophage dynamics and contributions to pathogenic traits

Polylysogeny is frequently considered to be the result of an adaptive evolutionary process in which prophages confer fitness and/or virulence factors, thus making them important for evolution of both bacterial populations and infectious diseases. The Enterococcus faecalis V583 isolate belongs to the high-risk clonal complex 2 that is particularly well adapted to the hospital environment. Its genome carries 7 prophage-like elements (V583-pp1 to -pp7), one of which is ubiquitous in the species. In this study, we investigated the activity of the V583 prophages and their contribution to E. faecalis biological traits. We systematically analyzed the ability of each prophage to excise from the bacterial chromosome, to replicate and to package its DNA. We also created a set of E. faecalis isogenic strains that lack from one to all six non-ubiquitous prophages by mimicking natural excision. Our work reveals that prophages of E. faecalis V583 excise from the bacterial chromosome in the presence of a fluoroquinolone, and are able to produce active phage progeny. Intricate interactions between V583 prophages were also unveiled: i) pp7, coined EfCIV583 for E. faecalis chromosomal island of V583, hijacks capsids from helper phage 1, leading to the formation of distinct virions, and ii) pp1, pp3 and pp5 inhibit excision of pp4 and pp6. The hijacking exerted by EfCIV583 on helper phage 1 capsids is the first example of molecular piracy in Gram positive bacteria other than staphylococci. Furthermore, prophages encoding platelet-binding-like proteins were found to be involved in adhesion to human platelets, considered as a first step towards the development of infective endocarditis. Our findings reveal not only a role of E. faecalis V583 prophages in pathogenicity, but also provide an explanation for the correlation between antibiotic usage and E. faecalis success as a nosocomial pathogen, as fluoriquinolone may provoke release of prophages and promote gene dissemination among isolates.

Enterococcus faecalis is a member of the core-microbiome of the human gastrointestinal tract. In the last decades however, this bacterial species has emerged as a major cause of hospital-acquired infections worldwide. Some isolates are particularly adapted to the hospital environment, and this adaptation was recently linked with enrichment in mobile genetic elements including prophages, which are chromosomal integrated genomes of bacterial viruses. We characterized the biological prophage activity in an E. faecalis strain of clinical origin that harbors 7 prophages. Six active prophages exhibit intricate interactions, one of which is involved in a molecular piracy phenomenon. We also established, for the first time, a direct correlation between prophage and adhesion to human platelets, an initial step towards infective endocarditis. Finally, we showed that fluoroquinolone increases prophage activity and can thus contribute to horizontal gene spreading. Overall, we provide evidence that prophages are key players in E. faecalis evolution towards pathogenicity.

Realistic representation of Bacillus subtilis biofilms architecture using combined microscopy (CLSM, ESEM and FESEM)

In this contribution, we used a set of microscopic techniques including confocal laser scanning microscopy (CLSM), environmental scanning electron microscopy (ESEM) and field emission scanning electron microscopy (FESEM) to analyze the three-dimensional spatial arrangement of cells and their surrounding matrix in Bacillus subtilis biofilm. The combination of the different techniques enabled a deeper and realistic deciphering of biofilm architecture by providing the opportunity to overcome the limits of each single technique.

Pilus biogenesis in Lactococcus lactis: molecular characterization and role in aggregation and biofilm formation

The genome of Lactococcus lactis strain IL1403 harbors a putative pilus biogenesis cluster consisting of a sortase C gene flanked by 3 LPxTG protein encoding genes (yhgD, yhgE, and yhhB), called here pil. However, pili were not detected under standard growth conditions. Over-expression of the pil operon resulted in production and display of pili on the surface of lactococci. Functional analysis of the pilus biogenesis machinery indicated that the pilus shaft is formed by oligomers of the YhgE pilin, that the pilus cap is formed by the YhgD pilin and that YhhB is the basal pilin allowing the tethering of the pilus fibers to the cell wall. Oligomerization of pilin subunits was catalyzed by sortase C while anchoring of pili to the cell wall was mediated by sortase A. Piliated L. lactis cells exhibited an auto-aggregation phenotype in liquid cultures, which was attributed to the polymerization of major pilin, YhgE. The piliated lactococci formed thicker, more aerial biofilms compared to those produced by non-piliated bacteria. This phenotype was attributed to oligomers of YhgE. This study provides the first dissection of the pilus biogenesis machinery in a non-pathogenic Gram-positive bacterium. Analysis of natural lactococci isolates from clinical and vegetal environments showed pili production under standard growth conditions. The identification of functional pili in lactococci suggests that the changes they promote in aggregation and biofilm formation may be important for the natural lifestyle as well as for applications in which these bacteria are used.

First evidence of bacterial biofilms in the anaerobe part of scalp hair follicles: a pilot comparative study in folliculitis decalvans

BACKGROUND

The cause of folliculitis decalvans (FD) remains unknown. We hypothesized that a bacterial biofilm could be involved in its pathogenesis.

OBJECTIVE

To assess the presence or not of a bacterial biofilm in the hair roots of the scalp in FD.

PATIENTS AND METHODS

Hairs plucked from four patients and three controls were examined by field emission scanning electron microscopy (FESEM) and confocal laser scanning microscopy (CLSM).

RESULTS

Bacterial communities organized as biofilms were observed both by FESEM and CLSM in the under infundibular part of hair follicles in all patients and in two of the three controls. In patients and controls, these biofilms were formed exclusively of bacilli of comparable shapes.

CONCLUSION

This pilot study provides the first evidence of the presence of bacterial biofilms in the infra infundibular part of human scalp hair follicles. These biofilms were detected both in FD patients and controls, suggesting their ubiquity as a commensal biofilm with a possible pathogenic shift in FD.

Characteristics of microbial biofilm on wooden vats ('gerles') in PDO Salers cheese

The purpose of this study was to characterize microbial biofilms from 'gerles' (wooden vats for making PDO Salers cheese) and identify their role in milk inoculation and in preventing pathogen development. Gerles from ten farms producing PDO Salers cheese were subjected to microbial analysis during at least 4 periods spread over two years. They were distinguished by their levels of Lactobacillus (between 4.50 and 6.01 log CFU/cm(2)), Gram negative bacteria (between 1.45 and 4.56 log CFU/cm(2)), yeasts (between 2.91 and 5.57 log CFU/cm(2)), and moulds (between 1.72 and 4.52 log CFU/cm(2)). They were then classed into 4 groups according their microbial characteristics. These 4 groups were characterized by different milk inoculations (with either sour whey or starter culture, daily or not), and different washing procedures (with water or whey from cheese making). The farm gerles were not contaminated by Salmonella, Listeria monocytogenes or Staphylococcus aureus. Only one slight, punctual contamination was found on one gerle among the ten studied. Even when the milk was deliberately contaminated with L. monocytogenes and S. aureus in the 40 L experimental gerles, these pathogens were found neither on the gerle surfaces nor in the cheeses. Using 40 L experimental gerles it was shown that the microbial biofilms on the gerle surfaces formed in less than one week and then remained stable. They were mainly composed of a great diversity of lactic acid bacteria (Leuconostoc pseudomesenteroides, Lactococcus lactis, Lactobacillus casei, Lactobacillus plantarum, Lactobacillus hilgardii,…), Gram positive catalase positive bacteria (Curtobacterium flaccumfaciens, Curtobacterium oceanosedimentum Citrococcus spp., Brachybacterium rhamnosum, Kocuria rhizophila, Arthrobacter spp.…) and yeast (Kluyveromyces lactis, Kluyveromyces marxianus). In less than 1 min, even in a 500 L farm gerle, the gerle's microbial biofilm can inoculate pasteurized milk with micro-organisms at levels superior to those in raw milk.

The effect of in vitro growth conditions on the resistance of Acanthamoeba cysts

Despite increasing concerns of direct pathogenicity and/or their role as hosts for other microorganisms there are currently no standard methods for the inactivation of amoebae that belong to the genus Acanthamoeba. Methods used to grow amoebae and produce cysts for these tests may be important as they can dramatically modify cyst susceptibility. We compared resistance of cysts produced from trophozoites grown in peptone-yeast extract-glucose broth or by feeding on HEp-2 cells and then encysted in Neff's medium. We observed that trophozoites grown using HEp-2 cells as a nutrient source produce cysts that are significantly more resistant to SDS and to most biocides tested, including heat. Increased resistance is likely due to a higher proportion of mature cysts presenting thicker cell walls as demonstrated using transmission electron microscopy. This was confirmed by calcofluor white staining demonstrating higher cellulose content in cysts produced from trophozoites grown using HEp-2 cells as a feeding source. These results demonstrate that not only methods used to produce cysts from trophozoites are critical, but that methods used to grow trophozoites before encystment should also be chosen carefully. This should be taken into account for the development of protocols to evaluate biocides and antimicrobials against amoebal cysts.

The canine oocyte: uncommon features of in vivo and in vitro maturation

The biology of the canine oocyte is unusual compared with that of other mammalian females. The present paper reviews both in vivo and in vitro specificities of canine oocytes. Final follicular growth in the bitch is characterised by an early appearance of LH binding sites in the granulosa, a high proportion of polyovular follicles and a preovulatory luteinisation, starting at the time of the LH surge. Through follicular fluid, preovulatory oocytes are thus exposed to high levels of progesterone, as high as 1000-fold plasma concentrations. The composition of the follicular fluid is affected by the size of the female. The more specific aspect of oocyte biology in the bitch is ovulation: oocytes are expelled immature, at the Prophase I stage. Ovulatory follicles are 6–8 mm in diameter, releasing oocytes from 110 µm, with dark cytoplasm. Resumption of meiosis occurs from 48 h postovulation, MII stages appearing 48–54 h after ovulation. The mechanisms controlling such a late meiotic resumption are still unknown. Granulosa cells seem to play a central role as in other mammalian species, but not with cAMP as the principal mediator. The importance of a transient reactivation of oocyte transcription a few hours before meiotic resumption is to be explored. These specific features may contribute to the low efficiency of IVM. Only 10–20% oocytes reach the metaphase stage and suffer from a poor cytoplasmic maturation. Moreover, in vitro culture of canine oocytes is associated with a high proportion of degeneration. To date, IVM of the oocytes is the main limiting factor for the development of assisted reproductive techniques in the canine. A better knowledge of the basic physiology of folliculogenesis and the molecular mechanisms controlling oocyte meiosis resumption in this species may allow us to overcome this obstacle.

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.

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

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.

Gliding arc discharge in the potato pathogen Erwinia carotovora subsp. atroseptica: mechanism of lethal action and effect on membrane-associated molecules

Gliding arc (glidarc) discharge is a physicochemical technique for decontamination at atmospheric pressure and ambient temperature. It leads to the destruction of bacterial phytopathogens responsible for important losses in industrial agriculture, namely, Erwinia spp., without the formation of resistant forms. We investigated the effect of a novel optimized prototype allowing bacterial killing without lag time. This prototype also decreases the required duration of treatment by 50%. The study of the time course effect of the process on bacterial morphology suggests that glidarc induces major alterations of the bacterial membrane. We showed that glidarc causes the release of bacterial genomic DNA. By contrast, an apparent decrease in the level of extractible lipopolysaccharide was observed; however, no changes in the electrophoretic pattern and cytotoxic activity of the macromolecule were noted. Analysis of extractible proteins from the outer membrane of the bacteria revealed that glidarc discharge induces the release of these proteins from the lipid environment, but may also be responsible for protein dimerization and/or aggregation. This effect was not observed in secreted enzymatic proteins, such as pectate lyase. Analysis of the data supports the hypothesis that the plasma generated by glidarc discharge is acting essentially through oxidative mechanisms. Furthermore, these results indicate that, in addition to effectively destroying bacteria, glidarc discharge should be used to improve the extraction of bacterial molecules.

Importance of bacterial surface properties to control the stability of emulsions

In colloidal media such as emulsions or food matrixes, the stability results from physicochemical interactions. The same type of interaction is involved in the attachment processes of microorganisms, through their surface properties, to interfaces. When bacteria are present in a food matrix, it is probable that their surface interacts with the other constituents. In this paper, the involvement of bacterial surface properties of Lactococcus lactis subsp lactis biovar diacetylactis (LLD) on the stability of model emulsions has been studied. The hydrophobic and electrostatic cell-surface properties were characterized by the MATH method and by microelectrophoresis, respectively. The oil-in-water emulsions were stabilized by various surface-active compounds, CTAB, SDS or Tween 20, giving differently charged droplets. Two strains with different surface characteristics were added to the emulsion. Contrasting with emulsions made with the non-ionic surfactant, for which the stability was not modified by the addition of bacteria, the emulsions made with ionic surface-active compounds were unstable in the presence of bacteria when the bacterial surface charge was opposite to the one of the emulsion droplets. Moreover, aggregation and flocculation phenomena were observed for emulsions stabilized with the cationic surfactant, particularly for more negatively charged bacteria. The effect of bacteria on the emulsion stability depended on the strain which shows the importance of the choice of the microorganism according to of the characteristics of the colloidal media to obtain a stable system. In addition, these results suggest that the interactions between bacteria and other food components can influence the position of bacteria in food matrixes.

Adsorption on stainless steel surfaces of biosurfactants produced by gram-negative and gram-positive bacteria: Consequence on the bioadhesive behavior of Listeria monocytogenes

The ability of adsorbed biosurfactants (Pf and Lb) obtained from gram-negative bacterium (Pseudomonas fluorescens) or gram-positive bacterium (Lactobacillus helveticus) to inhibit adhesion of four listerial strains to stainless steel was investigated. These metallic surfaces were characterized using the following complementary analytical techniques: contact-angle measurements (CAM), atomic force microscopy (AFM), polarization modulation-infrared reflection-adsorption spectroscopy (PM-IRRAS) and X-ray photoelectron spectroscopy (XPS). Contact-angles with polar liquids (water and formamide) indicated that the stainless steel surface covered with adsorbed biosurfactant was more hydrophilic and electron-donating than bare stainless steel. The surface characterization by XPS and PM-IRRAS revealed that conditioning the stainless steel changes the substrate in two ways, by modifying the surface alloy composition and by leaving an thin adsorbed organic layer. AFM observations enabled to say that the layer covered entirely the surface and was probably thicker (with patches) in the case of Pf-conditioned surfaces compared to the Lb-conditioned ones, which seemed to be less homogeneous. Though the added layer was thin, significant chemical changes were observed that can account for drastic modifications in the surface adhesive properties. As a matter of fact, adhesion tests showed that both used biosurfactants were effective by decreasing strongly the level of contamination of stainless steel surfaces by the four strains of Listeria monocytogenes. The more important decrease concerned the CIP104794 and CIP103573 strains (>99.7%) on surface conditioned by L. helveticus biosurfactant. A less reduced phenomenon (75.2%) for the CIP103574 strain on stainless steel with absorbed biosurfactant from P. fluorescens was observed. Whatever the strain of L. monocytogenes and the biosurfactant used, this antiadhesive biologic coating reduced both total adhering flora and viable and cultivable adherent bacteria on stainless steel surfaces. This study confirms that biosurfactants constitute an effective strategy to prevent microbial colonization of metallic surfaces by pathogenic bacteria like the food-borne pathogen L. monocytogenes.

Adsorption of a biosurfactant on surfaces to enhance the disinfection of surfaces contaminated with Listeria monocytogenes

The effects of sodium hypochlorite (NaOCl) and peracetic acid/hydrogen peroxide (PAH) on the inactivation of adherent Listeria monocytogenes LO28 cells were examined. The surfaces tested were stainless steel and polytetrafluoroethylene (PTFE) conditioned or not with an anionic biosurfactant produced by Pseudomonas fluorescens. Dilution-neutralization methods were used to assess the effectiveness of sanitizer solutions on planktonic and adherent cells. Tests were performed on L. monocytogenes cultivated at 37 degrees Celsius (body temperature) or 20 degrees Celsius (ambient temperature). The results demonstrated that i) a total deficiency in nutrients induced by the incubation of cells in 0.15 M NaCl favored the action of NaOCl and PAH on planktonic cells; ii) by reducing the number of cells adhering to stainless steel, pre-conditioning of the surface with the biosurfactant reduced the level of contamination of the surface and thus favored the bactericidal activities of the disinfectants; and iii) the weak binding energies involved in the adsorption of the biosurfactant on PTFE surfaces resulted in there being no reduction by the polymer of the surface contamination. Furthermore, this study confirmed that adherent cells exhibited increased resistance to the actions of the disinfectants when compared to the resistance of planktonic cells.

Bacterial biofilm in seawater: cell surface properties of early-attached marine bacteria

The development of antifouling strategies in seawater requires knowledge of the physico-chemical properties of the cell surfaces of early adherent bacteria. The hydrophilic, electrostatic and the Lewis acid-base cell surface properties of eleven marine bacteria were characterized. Although these bacteria adhered to a hydrophilic support immersed for 3 and 6 h, they presented various physico-chemical properties. Eleven strains possessed a hydrophilic surface and five a hydrophobic surface. Although the majority of the bacteria presented an electron-donating character, some could not generate Lewis acid-base interactions with the support. On the other hand, all strains possessed an isoelectric point ranging from 2.2 to 3.4 and were negatively charged at the pH of seawater. Hydrophilicity was a preponderant property among these bacteria, but other properties should not be ignored. The development of new antifouling paints must take account all the possible interaction levels used by the bacteria to adhere to an immersed surface.

Comparison of the cell surface properties and growth characteristics of Listeria monocytogenes and Listeria innocua

Growth kinetics and physicochemical surface properties were compared for three Listeria strains with differing degrees of virulence: L. monocytogenes LO28; its isogenic, nonhemolytic mutant L. monocytogenes Bof415; and a nonvirulent species, L. innocua (strain Lin9). The influences of growth stage (mid-exponential phase, early stationary phase, and mid-stationary phase) and culture temperature (20 and 37 degrees C) were assessed by determining the electrical properties and the hydrophobic-hydrophilic and Lewis acid-base characteristics of the three strains. L. innocua, although taxonomically very similar to L. monocytogenes, exhibited physicochemical surface properties that differed significantly from those of L. monocytogenes LO28 and L. monocytogenes Bof415. Indeed, under our experimental conditions, L. innocua cells presented a more marked electronegative character (particularly when cultured at 20 degrees C), as well as greater variability in their Lewis acid-base characteristics as a function of temperature and growth stage. Furthermore, the growth kinetics of the three strains revealed the onset of a decay phase after 16 h of culture at 37 degrees C for the L monocytogenes Bof415 mutant. All of these results demonstrate that under our experimental conditions, the growth and/or physicochemical characteristics of the slightly pathogenic or nonpathogenic Listeria strains (Bof415 and Lin9) differed from those of the virulent strain (L. monocytogenes LO28). Consequently, the use of Listeria strains recognized as nonvirulent appeared to provide a model that was not fully suitable for simulating the bioadhesive behavior of the pathogenic strains involved in foodborne diseases.

Listeria monocytogenes LO28: surface physicochemical properties and ability to form biofilms at different temperatures and growth phases

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 degrees C, the biofilm structure was composed of aggregates with a three-dimensional shape, but significant detachment took place on PTFE at 37 degrees C. At 8 degrees 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.

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.

METHODS AND RESULTS

The biosurfactant was produced according to a simple, novel technique based on cultivation on nutrient agar. Adhesion studies were performed using L. monocytogenes cells cultured at 20 or 37 degrees C.

CONCLUSIONS

A substrate-dependent behaviour of the LO28 strain (larger number of cells adhering to stainless steel than to PTFE), and a significant reduction (< 90%) in microbial adhesion levels through the prior adsorption of biosurfactants on stainless steel surfaces, which can be related to a change in the electron-donor characteristics of this substratum, was demonstrated.

SIGNIFICANCE AND IMPACT OF THE STUDY

The prior adsorption of biosurfactants on solid surfaces may constitute a new and effective means of combating the implantation of pathogenic micro-organisms in food processing plants.

Listeria monocytogenes Scott A: cell surface charge, hydrophobicity, and electron donor and acceptor characteristics under different environmental growth conditions

We determined the variations in the surface physicochemical properties of Listeria monocytogenes Scott A cells that occurred under various environmental conditions. The surface charges, the hydrophobicities, and the electron donor and acceptor characteristics of L. monocytogenes Scott A cells were compared after the organism was grown in different growth media and at different temperatures; to do this, we used microelectrophoresis and the microbial adhesion to solvents method. Supplementing the growth media with glucose or lactic acid affected the electrical, hydrophobic, and electron donor and acceptor properties of the cells, whereas the growth temperature (37, 20, 15, or 8 degrees C) primarily affected the electrical and electron donor and acceptor properties. The nonlinear effects of the growth temperature on the physicochemical properties of the cells were similar for cells cultivated in two different growth media, but bacteria cultivated in Trypticase soy broth supplemented with 6 g of yeast extract per liter (TSYE) were slightly more hydrophobic than cells cultivated in brain heart infusion medium (P < 0.05). Adhesion experiments conducted with L. monocytogenes Scott A cells cultivated in TSYE at 37, 20, 15, and 8 degrees C and then suspended in a sodium chloride solution (1.5 x 10(-1) or 1.5 x 10(-3) M NaCl) confirmed that the cell surface charge and the electron donor and acceptor properties of the cells had an influence on their attachment to stainless steel.