Diversity of the surface properties of Lactococci and consequences on adhesion to food components

An in vitro evaluation of the effect of antimicrobial treatment on bovine mammary microbiota

Antimicrobial-resistant bacteria have been an increasing problem in human medicine and animal husbandry since the introduction of antimicrobials on the market in the 1940s. Over the last decades, efforts to reduce antimicrobial usage in animal husbandry have been shown to limit the development of resistant bacteria. Despite this, antimicrobial-resistant bacteria are still commonly detected and isolated worldwide. In this study, we investigated the presence of antimicrobial-resistant bacteria in bovine milk samples using a multiple approach based on culturing and amplicon sequencing. We first enriched milk samples obtained aseptically from bovine udders in the presence of two antimicrobials commonly used to treat mastitis and then described the resistant microbiota by amplicon sequencing and isolate characterization. Our results show that several commensal species and mastitis pathogens harbor antimicrobial resistance and dominate the enriched microbiota in milk in presence of antimicrobial agents. The use of the two different antimicrobials selected for different bacterial taxa and affected the overall microbial composition. These results provide new information on how different antimicrobials can shape the microbiota which is able to survive and reestablish in the udder and point to the fact that antimicrobial resistance is widely spread also in commensal species.

Strain- and serotype-dependent affinity of Shiga toxin-producing Escherichia coli for bovine milk fat globules

Shiga toxin-producing Escherichia coli (STEC) are widely detected in raw milk products intended for human consumption. Although STEC are a worldwide public health problem, the pathogenicity of STEC in cheese remains unclear. In fact, bacterial association with compounds in raw milk cheeses could reduce their pathogenicity. A previous study showed the association of 2 STEC strains with raw milk cream in a natural creaming assay. Different concentrations of each strain were required to saturate the cream. In this study, we hypothesized that all STEC strains could be associated with milk fat globules (MFG) in raw milk and that the bacterial load required for saturation of the cream is serotype dependent. We evaluated the affinity of STEC strains belonging to the O157:H7, O26:H11, and O103:H2 serotypes for bovine raw milk cream and analyzed saturation of the cream layer by natural creaming assay. We used 12 STEC strains and 3 strains belonging to another pathotype to assess the effects of serotypes on this phenomenon. We performed sucrose density gradient centrifugation assays with 2 STEC model strains to confirm the results obtained by natural creaming. The localization of STEC within MFG-enriched creams was observed by confocal and electron microscopy. We recovered approximately 10 times more STEC from the cream layer after natural creaming than from raw bovine milk. The concentration of STEC required to saturate the cream layer (the saturation concentration) was estimated for each strain by nonlinear regression, highlighting a strain and serotype effect. Moreover, the concentration of STEC in the cream was milk fat level dependent. However, even in nonsaturating conditions, a high level of STEC was still present in the aqueous phase, after fat separation. Thus, natural creaming should not be used as the sole preventive measure to remove STEC from naturally contaminated raw milk. The results of our study suggest that cream saturation is a complex mechanism, most likely involving specific interactions between STEC and raw MFG.

Method-induced variation in the bacterial cell surface hydrophobicity MATH test

Bacterial cell surface hydrophobicity is a relevant property in determining the ability of bacteria to adhere to inert surfaces. This property has been measured using the microbial adhesion to hydrocarbon (MATH) test. Several reports in the literature establish the percentage of adhesion to hydrocarbons (PoAtH) value produced by the MATH test for a broad variety of bacteria. Discrepancies in PoAtH values reported for the same strain of a specific microorganism suggest that some method-induced variation may exist, as different research teams employ different versions of the assay. The objective of the present study was to compare the performance of different versions of the MATH test as reported in the literature, to quantify the magnitude of the method-induced variation on PoAtH values. The study demonstrated that PoAtH values are influenced twice as much by variations in the employed assay than by actual differences in cell surface composition or architecture. The two L. reuteri strains studied responded differently to changes in assay conditions showing 40 and 70% method-dependent variation for strain ATCC 53609 and 55730, respectively. These results highlight the need to properly standardize the MATH test to enable comparison of PoAtH values produced by independent research teams.

Microorganisms, the Ultimate Tool for Clean Label Foods?

Clean label is an important trend in the food industry. It aims at washing foods of chemicals perceived as unhealthy by consumers. Microorganisms are present in many foods (usually fermented), they exhibit a diversity of metabolism and some can bring probiotic properties. They are usually well considered by consumers and, with progresses in the knowledge of their physiology and behavior, they can become very precise tools to produce or degrade specific compounds. They are thus an interesting means to obtain clean label foods. In this review, we propose to discuss some current research to use microorganisms to produce clean label foods with examples improving sensorial, textural, health and nutritional properties.

Improving Human Health with Milk Fat Globule Membrane, Lactic Acid Bacteria, and Bifidobacteria

The milk fat globule membrane (MFGM), the component that surrounds fat globules in milk, and its constituents have gained significant attention for their gut function, immune-boosting properties, and cognitive-development roles. The MFGM can directly interact with probiotic bacteria, such as bifidobacteria and lactic acid bacteria (LAB), through interactions with bacterial surface proteins. With these interactions in mind, increasing evidence supports a synergistic effect between MFGM and probiotics to benefit human health at all ages. This important synergy affects the survival and adhesion of probiotic bacteria through gastrointestinal transit, mucosal immunity, and neurocognitive behavior in developing infants. In this review, we highlight the current understanding of the co-supplementation of MFGM and probiotics with a specific emphasis on their interactions and colocalization in dairy foods, supporting in vivo and clinical evidence, and current and future potential applications.

Characterization of adhesion between Limosilactobacillus reuteri and milk phospholipids by density gradient and gene expression

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The interaction between lactic acid bacteria and milk phospholipids can be semi-quantified

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Binding and interaction between milk phospholipids and LAB is mediated by gene modulation

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Two of three genes for surface adhesion corresponded directly with binding results

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This method identifies LAB that adhere tightly to the intestinal membranes

The benefits of fermented dairy products, in particular the presence of lactic acid bacteria (LAB) and milk phospholipids (MPL), seem to correlate with positive effects on human health. We hypothesize that one aspect of this benefit is the adhesion of LAB to the milk fat globule membrane via the interaction of LAB and MPL. Our first objective was to present a method to characterize and quantify such adhesion and investigate its association with a physical test. Our second objective was to further analyze the mechanism of interaction by analyzing expression of 3 previously reported surface binding-promoting genes (MapA, Cnb, and CmbA). We categorized adhesion between MPL and LAB by observing the distribution of MPL in corresponding bacterial cultures. Our working hypothesis was that any interaction or adhesion between these 2 components would yield differences in the distribution of MPL. Out of 122 LAB tested, 27% showed what could be characterized as adhesion; 38% of these strains were Limosilactobacillus reuteri. Further characterization of adhesion was carried out using an reverse transcription quantitative-PCR experiment, which demonstrated that the relative expression level of CmbA was positively associated with that adhesion. In addition, supplementation of MPL caused overexpression of MapA and Cnb in L. reuteri OSU-PECh-37A and OSU-PECh-48. This study indicated strain-specific adhesion between MPL and LAB and suggested that CmbA, which encodes a surface protein, is a potential factor involved in that adhesion. A better understanding of interactions between MPL and LAB may contribute to the design of new functional products and improve the delivery of these bioactive ingredients to their target site of action.

Mosaic-CLSM Assessment of Bacterial Spatial Distribution in Cosmetic Matrices According to Matrix Viscosity and Bacterial Hydrophobicity

The reliability of the challenge test depends, among other parameters, on the spatial distribution of microorganisms in the matrix. The present study aims to quickly identify factors that are susceptible to impair a uniform distribution of inoculated bacteria in cosmetic matrices in this context. We used mosaic confocal laser scanning microscopy (M-CLSM) to obtain rapid assessment of the impact of the composition and viscosity of cosmetic matrices on S. aureus spatial distribution. Several models of cosmetic matrices were formulated with different concentrations of two thickeners and were inoculated with three S. aureus strains having different levels of hydrophobicity. The spatial distribution of S. aureus in each matrix was evaluated according to the frequency distribution of the fluorescence values of at least 1350 CLSM images. We showed that, whatever the thickener used, an increasingly concentration of thickener results in increasingly bacterial clustered distribution. Moreover, higher bacterial hydrophobicity also resulted in a more clustered spatial distribution. In conclusion, CLSM-based method allows a rapid characterization of bacterial spatial distribution in complex emulsified systems. Both matrix viscosity and bacterial surface hydrophobicity affect the bacterial spatial distribution which can have an impact on the reliability of bacterial enumeration during challenge test.

Skin-associated lactic acid bacteria from North American bullfrogs as potential control agents of Batrachochytrium dendrobatidis

The fungal pathogen Batrachochytrium dendrobatidis (Bd) is the causative agent of chytridiomycosis and has been a key driver in the catastrophic decline of amphibians globally. While many strategies have been proposed to mitigate Bd outbreaks, few have been successful. In recent years, the use of probiotic formulations that protect an amphibian host by killing or inhibiting Bd have shown promise as an effective chytridiomycosis control strategy. The North American bullfrog (Lithobates catesbeianus) is a common carrier of Bd and harbours a diverse skin microbiota that includes lactic acid bacteria (LAB), a microbial group containing species classified as safe and conferring host benefits. We investigated beneficial/probiotic properties: anti-Bd activity, and adhesion and colonisation characteristics (hydrophobicity, biofilm formation and exopolysaccharide-EPS production) in two confirmed LAB (cLAB-Enterococcus gallinarum CRL 1826, Lactococcus garvieae CRL 1828) and 60 presumptive LAB (pLAB) [together named as LABs] isolated from bullfrog skin.We challenged LABs against eight genetically diverse Bd isolates and found that 32% of the LABs inhibited at least one Bd isolate with varying rates of inhibition. Thus, we established a score of sensitivity from highest (BdGPL AVS7) to lowest (BdGPL C2A) for the studied Bd isolates. We further reveal key factors underlying host adhesion and colonisation of LABs. Specifically, 90.3% of LABs exhibited hydrophilic properties that may promote adhesion to the cutaneous mucus, with the remaining isolates (9.7%) being hydrophobic in nature with a surface polarity compatible with colonisation of acidic, basic or both substrate types. We also found that 59.7% of LABs showed EPS synthesis and 66.1% produced biofilm at different levels: 21% weak, 29% moderate, and 16.1% strong. Together all these properties enhance colonisation of the host surface (mucus or epithelial cells) and may confer protective benefits against Bd through competitive exclusion. Correspondence analysis indicated that biofilm synthesis was LABs specific with high aggregating bacteria correlating with strong biofilm producers, and EPS producers being correlated to negative biofilm producing LABs. We performed Random Amplified Polymorphic DNA (RAPD)-PCR analysis and demonstrated a higher degree of genetic diversity among rod-shaped pLAB than cocci. Based on the LAB genetic analysis and specific probiotic selection criteria that involve beneficial properties, we sequenced 16 pLAB which were identified as Pediococcus pentosaceus, Enterococcus thailandicus, Lactobacillus pentosus/L. plantarum, L. brevis, and L. curvatus. Compatibility assays performed with cLAB and the 16 species described above indicate that all tested LAB can be included in a mixed probiotic formula. Based on our analyses, we suggest that E. gallinarum CRL 1826, L. garvieae CRL 1828, and P. pentosaceus 15 and 18B represent optimal probiotic candidates for Bd control and mitigation.

Characterization of difference in structure and function of fresh and mastitic bovine milk fat globules

Characterization of milk fat globule (MFG) was performed to investigate the difference in MFG membrane (MFGM) between fresh and mastitis Holstein Friesian cow milk. Lipid distribution investigated by exogenous phospholipids using microscopy showed higher phospholipid content in fresh compared to mastitic MFGM. Xanthine oxidase assay indicative of membrane impairment revealed lower activity in mastitic samples compared to fresh globules. Of note, significantly higher roughness of globule surface and zeta potential was observed in mastitis compared to fresh globules. Influence of globule membrane on the interaction with L. fermentum demonstrated preferential adhesion of bacteria to fresh compared to mastitic globules including enhanced extent of binding. Results of the present study provides an insight of the interfacial changes occurring at the globule surface as well as highlighting the importance of selective bacterial interaction with milk components for the potential development of functional food with relevance to human health.

Transcriptional response of Lactococcus lactis during bacterial emulsification

Microbial surface properties are important for interactions with the environment in which cells reside. Surface properties of lactic acid bacteria significantly vary and some strains can form strong emulsions when mixed with a hydrocarbon. Lactococcus lactis NCDO712 forms oil-in-water emulsions upon mixing of a cell suspension with petroleum. In the emulsion the bacteria locate at the oil-water interphase which is consistent with Pickering stabilization. Cells of strain NCDO712 mixed with sunflower seed oil did not stabilize the oil droplets. This study shows that the addition of either ethanol or ammonium sulfate led to cell aggregation, which subsequently allowed stabilizing oil-in-water emulsions. From this, we conclude that bacterial cell aggregation is important for emulsion droplet stabilization. To determine how bacterial emulsification influences the microbial transcriptome RNAseq analysis was performed on lactococci taken from the oil-water interphase. In comparison to cells in suspension 72 genes were significantly differentially expressed with a more than 4-fold difference. The majority of these genes encode proteins involved in transport processes and the metabolism of amino acids, carbohydrates and ions. Especially the proportion of genes belonging to the CodY regulon was high. Our results also point out that in a complex environment such as food fermentations a heterogeneous response of microbes might be caused by microbe-matrix interactions. In addition, microdroplet technologies are increasingly used in research. The understanding of interactions between bacterial cells and oil-water interphases is of importance for conducting and interpreting such experiments.

Test parameters and cell chain length of Streptococcus thermophilus affect the microbial adhesion to hydrocarbons assay: a methodical approach

The microbial adhesion to hydrocarbons (MATH) test is one of the most common method to determine the hydrophobicity of cell surfaces. Despite its prevalence, no standard test parameters are used in literature, making a direct comparison of data almost impossible. Criticism also focuses on test parameters that may mask hydrophobic interactions and hence lead to erroneous test results. We methodically investigated the impact of different MATH test parameters on the calculation of the cell surface hydrophobicity of Streptococcus thermophilus, a widespread exopolysaccharide-producing lactic acid bacterium used in the production of fermented milk products. Besides composition and ionic strength of the buffer used for cell re-suspension, we observed a pronounced time dependency of the turbidity of the cell suspension during phase separation due to sedimentation and/or cell lysis. A new modification of the MATH assay was applied to enable the determination of cell surface hydrophobicity of long chain-forming bacteria. As the cell surface hydrophobicity was not altered during exponential growth phase, we assume that the cell surface and its capsular exopolysaccharide layer are not changed during cultivation.

Deletion of D-Lactate Dehydrogenase A in Neisseria meningitidis Promotes Biofilm Formation Through Increased Autolysis and Extracellular DNA Release

Neisseria meningitidis is a Gram-negative bacterium that asymptomatically colonizes the human nasopharyngeal mucosa. Pilus-mediated initial adherence of N. meningitidis to the epithelial mucosa is followed by the formation of three-dimensional aggregates, called microcolonies. Dispersal from microcolonies contributes to the transmission of N. meningitidis across the epithelial mucosa. We have recently discovered that environmental concentrations of host cell-derived lactate influences N. meningitidis microcolony dispersal. Here, we examined the ability of N. meningitidis mutants deficient in lactate metabolism to form biofilms. A lactate dehydrogenease A (ldhA) mutant had an increased level of biofilm formation. Deletion of ldhA increased the N. meningitidis cell surface hydrophobicity and aggregation. In this study, we used FAM20, which belongs to clonal complex ST-11 that forms biofilms independently of extracellular DNA (eDNA). However, treatment with DNase I abolished the increased biofilm formation and aggregation of the ldhA-deficient mutant, suggesting a critical role for eDNA. Compared to wild-type, the ldhA-deficient mutant exhibited an increased autolytic rate, with significant increases in the eDNA concentrations in the culture supernatants and in biofilms. Within the ldhA mutant biofilm, the transcription levels of the capsule, pilus, and bacterial lysis genes were downregulated, while norB, which is associated with anaerobic respiration, was upregulated. These findings suggest that the absence of ldhA in N. meningitidis promotes biofilm formation and aggregation through autolysis-mediated DNA release.

Cell Surface Properties of Lactococcus lactis Reveal Milk Protein Binding Specifically Evolved in Dairy Isolates

Surface properties of bacteria are determined by the molecular composition of the cell wall and they are important for interactions of cells with their environment. Well-known examples of bacterial interactions with surfaces are biofilm formation and the fermentation of solid materials like food and feed. Lactococcus lactis is broadly used for the fermentation of cheese and buttermilk and it is primarily isolated from either plant material or the dairy environment. In this study, we characterized surface hydrophobicity, charge, emulsification properties, and the attachment to milk proteins of 55 L. lactis strains in stationary and exponential growth phases. The attachment to milk protein was assessed through a newly developed flow cytometry-based protocol. Besides finding a high degree of biodiversity, phenotype-genotype matching allowed the identification of candidate genes involved in the modification of the cell surface. Overexpression and gene deletion analysis allowed to verify the predictions for three identified proteins that altered surface hydrophobicity and attachment of milk proteins. The data also showed that lactococci isolated from a dairy environment bind higher amounts of milk proteins when compared to plant isolates. It remains to be determined whether the alteration of surface properties also has potential to alter starter culture functionalities.

Biofilm formation and antibiotic susceptibility in dispersed cells versus planktonic cells from clinical, industry and environmental origins

We examined the cell-surface physicochemical properties, the biofilm formation capability and the antibiotic susceptibility in dispersed cells (from an artificial biofilm of alginate beads) and compared with their planktonic (free-swimming) counterparts. The strains used were from different origins, such as clinical (Acinetobacter baumannii AB4), cosmetic industry (Klebsiella oxytoca EU213, Pseudomonas aeruginosa EU190), and environmental (Halomonas venusta MAT28). In general, dispersed cells adhered better to surfaces (measured as the "biofilm index") and had a greater hydrophobicity [measured as the microbial affinity to solvents (MATS)] than planktonic cells. The susceptibility to two antibiotics (ciprofloxacin and tetracycline) of dispersed cells was higher compared with that of their planktonic counterparts (tested by the "bactericidal index"). Dispersed and planktonic cells exhibited differences in cell permeability, especially in efflux pump activity, which could be related to the differences observed in susceptibility to antibiotics. At 1 h of biofilm formation in microtiter plates, dispersed cells treated with therapeutic concentration of ciprofloxacin yielded a lower biofilm index than the control dispersed cells without ciprofloxacin. With respect to the planktonic cells, the biofilm index was similar with and without the ciprofloxacin treatment. In both cases there were a reduction of the number of bacteria measured as viable count of the supernatant. The lower biofilm formation in dispersed cells with ciprofloxacin treatment may be due to a significant increase of biofilm disruption with respect to the biofilm from planktonic cells. From a clinical point of view, biofilms formed on medical devices such as catheters, cells that can be related to an infection were the dispersed cells. Our results showed that early treatment with ciprofloxacin of dispersed cells could diminishe bacterial dispersion and facilitate the partial elimination of the new biofilm formed.

Characterization of Linoleate 10-Hydratase of Lactobacillus plantarum and Novel Antifungal Metabolites

Lactobacilli convert linoleic acid to the antifungal compound 10-hydroxy-12-octadecenoic acid (10-HOE) by linoleate 10-hydratase (10-LAH). However, the effect of this conversion on cellular membrane physiology and properties of the cell surface have not been demonstrated. Moreover, Lactobacillus plantarum produces 13-hydroxy-9-octadecenoic acid (13-HOE) in addition to 10-HOE, but the antifungal activity of 13-HOE was unknown. Phylogenetic analyses conducted in this study did not differentiate between 10-LAH and linoleate 13-hydratase (13-LAH). Thus, linoleate hydratases (LAHs) must be characterized through their differences in their activities of linoleate conversion. Four genes encoding putative LAHs from lactobacilli were cloned, heterologous expressed, purified and identified as FAD-dependent 10-LAH. The unsaturated fatty acid substrates stimulated the growth of lactobacilli. We also investigated the role of 10-LAH in ethanol tolerance, membrane fluidity and hydrophobicity of cell surfaces in lactobacilli by disruption of lah. Compared with the L. plantarum lah deficient strain, 10-LAH in wild-type strain did not exert effect on cell survival and membrane fluidity under ethanol stress, but influenced the cell surface hydrophobicity. Moreover, deletion of 10-LAH in L. plantarum facilitated purification of 13-HOE and demonstration of its antifungal activity against Penicillium roqueforti and Aspergillus niger.

Neisseria meningitidis Polynucleotide Phosphorylase Affects Aggregation, Adhesion, and Virulence

Neisseria meningitidis autoaggregation is an important step during attachment to human cells. Aggregation is mediated by type IV pili and can be modulated by accessory pilus proteins, such as PilX, and posttranslational modifications of the major pilus subunit PilE. The mechanisms underlying the regulation of aggregation remain poorly characterized. Polynucleotide phosphorylase (PNPase) is a 3'-5' exonuclease that is involved in RNA turnover and the regulation of small RNAs. In this study, we biochemically confirm that NMC0710 is the N. meningitidis PNPase, and we characterize its role in N. meningitidis pathogenesis. We show that deletion of the gene encoding PNPase leads to hyperaggregation and increased adhesion to epithelial cells. The aggregation induced was found to be dependent on pili and to be mediated by excessive pilus bundling. PNPase expression was induced following bacterial attachment to human cells. Deletion of PNPase led to global transcriptional changes and the differential regulation of 469 genes. We also demonstrate that PNPase is required for full virulence in an in vivo model of N. meningitidis infection. The present study shows that PNPase negatively affects aggregation, adhesion, and virulence in N. meningitidis.

Effect of cream fermentation on microbiological, physicochemical and rheological properties of L. helveticus-butter

The primary objective of this study was to evaluate the physicochemical and rheological properties of butter produced by Lactobacillus helveticus fermented cream. The incorporation of putative probiotic - the L. helveticus, to ferment cream prior to butter production was anticipated to alter the nutritional composition of butter. Changes in crude macronutrients and the resultant modification relating to textural properties of butter induced upon metabolic activities of L. helveticus in cream were focused in this research. Fermented butter (LH-butter) was produced by churning the cream that was fermented by lactobacilli at 37 °C for 24 h. Physicochemical analysis, proximate analysis and rheology properties of LH-butter were compared with butter produced using unfermented cream (control). LH-butter showed a significantly (P<0.05) higher fat content and acid value; lower moisture and ash; and was softer than the control. Cream fermentation modified nutritional and textural properties of butter in which LH-butter contained higher health beneficial unsaturated fatty acids than the control and thus rendered the product softer. Its enrichment with probiotics could thus further enhance its functional property.

Lactic acid bacteria in dairy food: surface characterization and interactions with food matrix components

This review gives an overview of the importance of interactions occurring in dairy matrices between Lactic Acid Bacteria and milk components. Dairy products are important sources of biological active compounds of particular relevance to human health. These compounds include immunoglobulins, whey proteins and peptides, polar lipids, and lactic acid bacteria including probiotics. A better understanding of interactions between bioactive components and their delivery matrix may successfully improve their transport to their target site of action. Pioneering research on probiotic lactic acid bacteria has mainly focused on their host effects. However, very little is known about their interaction with dairy ingredients. Such knowledge could contribute to designing new and more efficient dairy food, and to better understand relationships between milk constituents. The purpose of this review is first to provide an overview of the current knowledge about the biomolecules produced on bacterial surface and the composition of the dairy matter. In order to understand how bacteria interact with dairy molecules, adhesion mechanisms are subsequently reviewed with a special focus on the environmental conditions affecting bacterial adhesion. Methods dedicated to investigate the bacterial surface and to decipher interactions between bacteria and abiotic dairy components are also detailed. Finally, relevant industrial implications of these interactions are presented and discussed.

Evaluation of anti-Listeria meat borne Lactobacillus for biofilm formation on selected abiotic surfaces

The ability of meat borne anti-Listeria Lactobacillus to form biofilms under different in vitro conditions and on abiotic surfaces was investigated. Biofilm formation by the adhesion to polystyrene microtiter plates was determined, this being higher for Lactobacillus curvatus CRL1532 and CRL705 and Lactobacillus sakei CRL1862. The physicochemical properties of the cell surface were relatively hydrophilic and acidic in character; L. sakei CRL1862 exhibiting the strongest autoaggregation. The adhesion of lactobacilli to stainless steel (SS) and polytetrafluoroethylene (PTFE) supports at 10°C was found to be maximal for L. sakei CRL1862 on SS after 6 days. When biofilm architecture was characterized by epifluorescence and SEM, L. sakei CRL1862 homogeneously covered the SS surface while cell clusters were observed on PTFE; the extracellular polymeric substance matrix adapted to the topography and hydrophilic/hydrophobic characteristics of each material. The feasibility of L. sakei CRL1862 to form biofilm on materials used in meat processing highlights its potential as a control strategy for Listeria monocytogenes biofilms.

Attachment and invasion of Neisseria meningitidis to host cells is related to surface hydrophobicity, bacterial cell size and capsule

We compared exemplar strains from two hypervirulent clonal complexes, strain NMB-CDC from ST-8/11 cc and strain MC58 from ST-32/269 cc, in host cell attachment and invasion. Strain NMB-CDC attached to and invaded host cells at a significantly greater frequency than strain MC58. Type IV pili retained the primary role for initial attachment to host cells for both isolates regardless of pilin class and glycosylation pattern. In strain MC58, the serogroup B capsule was the major inhibitory determinant affecting both bacterial attachment to and invasion of host cells. Removal of terminal sialylation of lipooligosaccharide (LOS) in the presence of capsule did not influence rates of attachment or invasion for strain MC58. However, removal of either serogroup B capsule or LOS sialylation in strain NMB-CDC increased bacterial attachment to host cells to the same extent. Although the level of inhibition of attachment by capsule was different between these strains, the regulation of the capsule synthesis locus by the two-component response regulator MisR, and the level of surface capsule determined by flow cytometry were not significantly different. However, the diplococci of strain NMB-CDC were shown to have a 1.89-fold greater surface area than strain MC58 by flow cytometry. It was proposed that the increase in surface area without changing the amount of anchored glycolipid capsule in the outer membrane would result in a sparser capsule and increase surface hydrophobicity. Strain NMB-CDC was shown to be more hydrophobic than strain MC58 using hydrophobicity interaction chromatography and microbial adhesion-to-solvents assays. In conclusion, improved levels of adherence of strain NMB-CDC to cell lines was associated with increased bacterial cell surface and surface hydrophobicity. This study shows that there is diversity in bacterial cell surface area and surface hydrophobicity within N. meningitidis which influence steps in meningococcal pathogenesis.

Application of whey protein micro-bead coatings for enhanced strength and probiotic protection during fruit juice storage and gastric incubation

CONTEXT

Coated whey protein micro-beads may improve probiotic protection and provide delayed cell-release mechanisms.

OBJECTIVE

Lactobacillus rhamnosus GG was encapsulated in whey protein micro-beads by droplet extrusion with coating via electrostatic deposition: primary-polysaccharide and secondary-whey protein.

MATERIALS AND METHODS

Storage studies were performed in cranberry and pomegranate juice (pH 2.4; 28 days; 4 and 25°C) followed by simulated ex vivo porcine gastric (pH 1.6) and intestinal (pH 6.6) digestion.

RESULTS AND DISCUSSION

After storage and simulated gastro-intestinal digestion, free cells, cells suspended in protein and cells encapsulated in alginate micro-beads, illustrated complete probiotic mortality, while coated micro-beads enhanced probiotic viability after juice storage (8.6 ± 0.1 log(10)CFUmL(-1)). Beads also showed significant binding of hydrophobic molecules. Coated micro-beads illustrated high gastric survival (9.5 ± 0.1 log(10)CFUmL(-1)) with 30 min delayed intestinal release relative to non-coated micro-beads.

CONCLUSIONS

Micro-bead coatings could be applied in delayed cell-release for targeted intestinal probiotic delivery.

Characterization of Lactobacillus reuteri interaction with milk fat globule membrane components in dairy products

A set of methods has been developed to study the adhesion between four Lactobacillus reuteri strains and the milk fat globule membrane (MFGM) components in dairy products. By combining sucrose density gradient (SDG) centrifugation and bacterial DNA quantification it was found which strains of L. reuteri were more strongly associated with the dairy products, and the results were corroborated by direct binding rate and force measurements made with optical tweezers. It was determined that strong binding was associated with hydrophobicity of the bacteria and that this hydrophobicity is correlated with the presence of LiCl-extractable protein on the surface of the bacteria. Confocal laser scanning microscopy (CLSM) allowed for the visualization of interactions between bacteria and MFGM. This study demonstrates that these methods can be used in combination to characterize, both qualitatively and quantitatively, the adhesion of lactic acid bacteria strains in dairy products.

Surface and adhesion properties of lactobacilli

The surface properties of lactobacilli are of significant technological importance as they determine the interaction of the bacterial cells with the gastrointestinal mucosa, and therefore influence their location in the gut and their functionality. Studying the surface of the bacteria is critical for understanding the adhesion process better. This review compiles the knowledge from studies on the characterization Lactobacillus surfaces and evaluates the potential relationship between the cells' physicochemical characteristics and their adhesive abilities. It also discusses the effect that the production processes, such as fermentation and drying, can exert on the surface properties and adhesion abilities of lactobacilli.

Biofilm-detached cells, a transition from a sessile to a planktonic phenotype: a comparative study of adhesion and physiological characteristics in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a pathogenic bacterium widely investigated for its high incidence in clinical environments and its ability to form strong biofilms. During biofilm development, sessile cells acquire physiological characteristics differentiating them from planktonic cells. But after treatment with disinfectants, or to ensure survival of the species in hostile environments, biofilm cells can detach. This complicates disinfection procedures. This study aimed to physiologically characterize cells detached from a P. aeruginosa biofilm and to compare them with their sessile and planktonic counterparts. We first tested planktonic growth kinetics and capacities to form new biofilms. Then we investigated cell-surface properties. And finally, we tested in vitro susceptibility to antibiotics. The results first indicated that sessile and detached cells have similar planktonic growth kinetics and cell-surface properties, distinguishable from those of planktonic cells. Interestingly, the three populations exhibited different biofilm-forming capacities, suggesting that there is a transitional phenotype between sessile and planktonic states, at least during the first hours following cell detachment. It is important to consider this observation when developing treatments to optimize disinfection processes. Surprisingly, the three populations showed the same antibiotic susceptibility profile.

Screening of surface properties and antagonistic substances production by lactic acid bacteria isolated from the mammary gland of healthy and mastitic cows

Bovine mastitis (BM) is a costly disease in dairy cattle production. The prevention and treatment of mastitis is performed by applying antimicrobial products that negatively affect milk quality. In the last years, the use of probiotic microorganisms to prevent infections in humans and animals has being aggressively studied. Samples from teat canal and milk (foremilk and stripping) were taken from healthy and mastitic mammary quarters. A screening of the surface properties and antagonistic substances production of lactic acid bacteria (LAB) isolated from the mammary gland was performed to select potential probiotic strains to prevent mastitis. Somatic cell count, physico-chemical and microbiological studies were carried out. Pre-selected microorganisms were genetically identified. Compared with stripping milk, foremilk showed lower levels of fat and higher levels of pH, density, microorganism numbers, lower percentage of strains with mean and high hydrophobicity and mean autoaggregation and higher number of strains able to produce hydrogen peroxide and bacteriocins. The other parameters analyzed were not statistically significant. One hundred and two LAB strains were isolated. Most of them had low degrees of hydrophobicity and autoaggregation. No correlation between these properties was found. Antagonistic metabolites were mainly produced by strains isolated from healthy quarters. Most of the pre-selected strains were identified as Streptococcus bovis and Weissella paramesenteroides. Three bacteriocin-producers were found and their products partially characterized. The results of this work are the basis for the further design of a specie-specific probiotic product able to prevent BM.

Surface physicochemical analysis of natural Lactococcus lactis strains reveals the existence of hydrophobic and low charged strains with altered adhesive properties

The cell surface physicochemical properties of 50 Lactococcus lactis strains of different subspecies and isolated from different origins (dairy, vegetal and animal) were examined. Cell surface hydrophobicity and Lewis acid-base properties were evaluated by affinity measurements to solvents in a partitioning test, while the global electrical charge of the cells was assessed by micro-electrophoresis using a laser zeta-meter. A global multivariate analysis of the results revealed a high natural diversity of L. lactis cell surface properties. While 52% of the strains present a hydrophilic and electronegative cell wall surface, a group of strikingly hydrophobic strains (12% of the strains) and a group of strains with unusual low charged surface (18%) were identified. Adhesion on polystyrene microtitre plates was evaluated for twelve strains selected from the multivariate analysis as representatives of the various observed cell wall surface physicochemical patterns. A significant correlation between adhesion, hydrophobicity and low electronegativity was observed when adhesion was performed in a low ionic strength suspending medium. The most adhesive strains were hydrophobic or low charged. The presence of repulsive electrostatic interactions led to a decrease in adhesion of the most negatively charged hydrophilic strains. The present study highlights the diversity of L. lactis cell surface physicochemical properties, diversity that could not be connected to the origin or to the subspecies of the strains.

Comparison of contact angle measurement and microbial adhesion to solvents for assaying electron donor-electron acceptor (acid-base) properties of bacterial surface

The electron donor-electron acceptor (acid-base properties) of cell surfaces of a series of bacteria were determined by two methods, namely, Microbial Adhesion to Solvents (MATS) and Contact Angle Measurements (CAM) combined with equation of Van Oss. The efficiency of these two methods was then compared. Pseudomonas aeruginosa ATCC 27853, Bacillus subtilis ILP 142B, Staphylococcus aureus ATCC 25923 and four Escherichia coli strains including HB101, AL52, O128B12 and ATCC 25922, acid-base properties were examined under the two different conditions mentioned above. The results showed that the correlation between acid-base properties determined by MATS and CAM was very weak. We have also found that when the microbial cell surface was electron donor by CAM method, similar result was found by MATS, but the reverse was not always true. In contrast, a good correlation between the two methods was obtained when the four E. coli strains were examined.

Relationship between the presence of the citrate permease plasmid and high electron-donor surface properties of Lactococcus lactis ssp. lactis biovar. diacetylactis

Some strains of Lactococcus lactis subspecies possess a citrate permease that enables them to utilize citrate and to produce diacetyl. Such strains are classified as diacetylactis biovariants (L. lactis ssp. lactis biovar. diacetylactis). We investigated the electron-donor surface properties of L. lactis strains and observed that the diacetylactis biovariants presented increased adhesion to electron-acceptor solvents (microbial adhesion to solvents electron-donor characteristics of cells of <27% for L. lactis and about 50% for L. lactis ssp. lactis biovar diacetylactis). We investigated the properties of a pCitP- derivative and observed for a diacetylactis biovariant strain a loss of the electron-donor characteristics falling from 47% for a pCitP+ strain to 8% for its pCitP- derivative. This suggests that the presence of high electron-donor characteristics on the surface of L. lactis results to a large extent from the presence of the citrate permease plasmid.