Adhesion to bile drain materials and physicochemical surface properties of Enterococcus faecalis strains grown in the presence of bile

Enterococcal-host interactions in the gastrointestinal tract and beyond

The gastrointestinal tract (GIT) is typically considered the natural niche of enterococci. However, these bacteria also inhabit extraintestinal tissues, where they can disrupt organ physiology and cause life-threatening infections. Here, we discuss how enterococci, primarily Enterococcus faecalis, interact with the intestine and other host anatomical locations such as the oral cavity, heart, liver, kidney, and vaginal tract. The metabolic flexibility of these bacteria allows them to quickly adapt to new environments, promoting their persistence in diverse tissues. In transitioning from commensals to pathogens, enterococci must overcome harsh conditions such as nutrient competition, exposure to antimicrobials, and immune pressure. Therefore, enterococci have evolved multiple mechanisms to adhere, colonize, persist, and endure these challenges in the host. This review provides a comprehensive overview of how enterococci interact with diverse host cells and tissues across multiple organ systems, highlighting the key molecular pathways that mediate enterococcal adaptation, persistence, and pathogenic behavior.

Exoproteome Perspective on the Bile Stress Response of Lactobacillus johnsonii

Probiotics must not only exert a health-promoting effect but also be capable of adapting to the harsh environment of the gastrointestinal (GI) tract. Probiotics in the GI tract must survive the cell wall-disrupting effect of bile acids. We investigated the exoproteome of Lactobacillus johnsonii PF01 and C1-10 under bile stress. A comparative analysis revealed the similarities between the two L. johnsonii exoproteomes, as well as their different responses to bile. The large number of metabolic proteins in L. johnsonii revealed its metabolic adaptation to meet protein synthesis requirements under bile stress. In addition, cell wall modifications occurred in response to bile. Furthermore, some extracellular proteins of L. johnsonii may have moonlighting function in the presence of bile. Enolase, L-lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, triosephosphate isomerase, 50s ribosomal protein L7/L12, and cellobiose-specific phosphotransferase system (PTS) sugar transporter were significantly upregulated under bile stress, suggesting a leading role in the collective bile stress response of L. johnsonii from its exoproteome perspective.

Enhancement of bile resistance by maltodextrin supplementation in Lactobacillus plantarum Lp-115

AIMS

To identify the mechanism in which way maltodextrin enhance bile tolerance in Lactobacillus plantarum Lp-115.

METHODS AND RESULTS

Based on determining the OD₆₀₀ value and counting the numbers of viable cells by the pour plate method, the results showed that maltodextrin could not promote the strain growth directly, but could enhance the tolerance of bile in Lp-115. The OD₆₀₀ value of L. plantarum Lp-115 cultured in MRSB broth with maltodextrin was three times higher than the control value. After supplementing the medium with 4·0% maltodextrin, the highest survival rate was observed when the bile concentration is 0.3%.

CONCLUSIONS

In summary, maltodextrin exhibited a significant improvement of bile tolerance and it could enhance cell hydrophobicity, shift the fatty acid composition of the membrane and induce the expression of a bile salt hydrolase gene (pva3) significantly.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report concerning the mechanism of maltodextrin enhancing the bile tolerance. This study promotes the application of maltodextrin as a choice to protect probiotic L. plantarum strains against the bile salt stress.

Surface properties of Enterococcus faecalis cells isolated from chicken hearts determine their low ability to form biofilms

Enterococcus faecalis is one of the most significant bacterial pathogens associated with the first-week mortality of chickens. Here, the surface properties of bacterial cells and the selected virulence factors of E. faecalis strains isolated from the hearts of clinically healthy broiler chickens were studied. Investigations were carried out on live and autoclaved cells. E. faecalis (ATCC 29212) was used as a reference strain. The bacterial cells revealed different haemolytic activities. Their surface free energy was dominated by the hydrophobic component. The cell walls of the bird isolates showed slightly weaker acidic characteristics than those of E. faecalis (ATCC 29212). Moreover, the bacterial cells from the chicken hearts showed higher electrophoretic mobility and surface electrical charge than the reference strain, and consequently demonstrated a low ability to form biofilms.

[Vancomycin-resistant enterococci (VRE). Recent results and trends in development of antibiotic resistance]

Enterococci (mainly E. faecalis, E. faecium) are important nosocomial pathogens predominantly affecting older and/or immunocompromised patients. The bacteria possess a broad spectrum of intrinsic and acquired antibiotic resistance properties. Among these, the transferrable glycopeptide resistance of the vanA and vanB genotypes in vancomycin-resistant enterococci (VRE; reservoir: E. faecium) as well as resistance to last resort antibiotics (e.g. linezolid and tigecycline) are of special concern. Enterococci (including VRE) are easily transferred in hospitals; however, colonizations are far more frequent than infections. Resistance frequencies for vancomycin in clinical E. faecium isolates have remained at a relatively constant level of 8-15% (but with local or regional variations) in recent years whereas frequencies for teicoplanin resistance have shown a slight decrease. Glycopeptide resistance trends correlate with a spread of hospital-associated E. faecium strains carrying the vanA and, with rising frequency in recent years, the vanB gene cluster, the latter being associated with teicoplanin susceptibility. This increased occurrence of vanB-positive E. faecium strains may be caused by an increased use of antibiotics selecting enterococci and VRE as well as due to methodological reasons (e.g. reduced EUCAST MIC-breakpoints for glycopeptides; increased use and sensitive performance of chromogenic VRE agars, increased use of molecular diagnostic assays).

Transcriptional responses of Enterococcus faecalis V583 to bovine bile and sodium dodecyl sulfate

Resistance to bile is a prerequisite property of the gastrointestinal bacterial flora. Bile acids are powerful detergents, and resistance to sodium dodecyl sulfate (SDS) has therefore often been considered relevant to studies of bile resistance. We have studied the effects of bovine bile (BB) and SDS on Enterococcus faecalis V583 by traditional growth studies and microarrays. Transcriptional responses were studied by time course experiments. In the presence of BB (V583-BB) or SDS (V583-SDS), 308 and 209 genes were identified as differentially expressed at one or more time points, respectively. In V583 treated with both BB and SDS (V583-BB-SDS), 254 genes showed differential expression. Detergents exert their toxic effects primarily on the microbial membrane. The enrichment of differentially transcribed genes that encode proteins with membrane-associated functions and/or locations indicates a major impact of all three treatments on the integrity and functionality of the cell membrane. Two gene clusters involved in fatty acid biosynthesis were repressed in V583-BB and V583-BB-SDS and partly induced in V583-SDS. Furthermore, two EmrB/QacA family drug resistance transporters and a vacuolar-type ATPase were induced in V583-BB and V583-BB-SDS. None of the putative bile salt hydrolase homologs in V583 showed differential expression during the bile treatments. The transcriptional profile of V583-BB-SDS was qualitatively more similar to the response in V583-BB than to that in V583-SDS, suggesting that the presence of bile suppresses the effects of SDS in V583-BB-SDS. The overall results presented here indicate that different mechanisms are involved in detergent resistance in E. faecalis.

Adhesion to medical device materials and biofilm formation capability of some species of enterococci in different physiological states

Enterococci may survive in adverse environments including the human body where bacteriocins, antibiotics, iron-limitation and immune response represent stressing conditions for bacteria that cause division block. In those conditions, bacteria present in the human body would hardly be in an exponentially growing phase but would mostly be in physiological states such as starvation or the viable but nonculturable (VBNC) state. The possibility that the starved and VBNC bacteria can maintain their ability to adhere to living and inanimate substrates is the first mandatory step for them potentially to cause an infection process. In this study it is shown that starved and stationary enterococcal cells are able to form biofilms on plastic material albeit with reduced efficiency as compared to growing cells. Moreover, although VBNC enterococcal forms are not capable of forming biofilms, Enterococcus faecalis and other enterococcal species of medical interest maintain their ability to synthesize the polymeric matrix for a limited period of time under adverse environmental conditions. The data presented, together with those regarding the maintenance of the division recovery potential already proved in nonculturable bacteria, further support the possibility for the VBNC and other nondividing bacterial forms to have a role as infectious agents and to constitute a risk to human health.

Plastic biliary stent occlusion: factors involved and possible preventive approaches

Endoscopic biliary stenting is today the most common palliative treatment for patients suffering from obstructive jaundice associated with malignant hepatobiliary tumors or benign strictures. However, recurrent jaundice, with or without cholangitis, is a major complication of a biliary endoprosthesis insertion. Thus, stent removal and replacement with a new one frequently occurs as a consequence of device blockage caused by microbial biofilm growth and biliary sludge accumulation in the lumen. Factors and mechanisms involved in plastic stent clogging arising from epidemiological, clinical and experimental data, as well as the possible strategies to prevent biliary stent failure, will be reviewed and discussed.

Implant infections due to enterococci: role of capsular polysaccharides and biofilm

Enterococci are natural inhabitants of the gastrointestinal tract and of the female genital tract of humans and many animals. In recent years, enterococci have been increasingly recognized as important human pathogens causing infections associated with medical devices. Their resistance to most antimicrobial agents and their ability to form biofilm has contributed to the increasing incidence of nosocomial enterococcal infections. Enterococci possess a capsular polysaccharide composed of a glycerol-teichoic acid-like molecule consisting of repeating units of 6-alfa-D-glucose-1-2-glycerol-3-PO4 , substituted on carbon 2 with a alfa-2,1-linked molecule of glucose. Using both immunologic and genetic data E. faecalis can be assigned to specific serotypes based on capsular polysaccharides. Clinical examples of foreign-body infections due to enterococci are described, comprising infections of artificial joints, implanted intravascular catheters, artificial hearts and artificial valves, stents, liquor shunt devices, and intraocular infections. Methods to prevent and/or treat enterococcal infections are presented.

Microbial adhesion in flow displacement systems

Flow displacement systems are superior to many other (static) systems for studying microbial adhesion to surfaces because mass transport and prevailing shear conditions can be adequately controlled and notoriously ill-defined slight rinsing steps to remove so-called "loosely adhering organisms" can be avoided. In this review, we present the basic background required to calculate mass transport and shear rates in flow displacement systems, focusing on the parallel plate flow chamber as an example. Critical features in the design of flow displacement systems are discussed, as well as different strategies for data analysis. Finally, selected examples of working with flow displacement systems are given for diverse biomedical applications.

Enterococcus faecalis strains show culture heterogeneity in cell surface charge

Adhesion of micro-organisms to biotic and abiotic surfaces is an important virulence factor and involves different types of interactions.Enterococcus faecalis, a human commensal and an important opportunistic pathogen, has the ability to adhere to surfaces. Biliary stents frequently become clogged with bacterial biofilms, withE. faecalisas one of the predominant species. SixE. faecalisstrains isolated from clogged biliary stents were investigated for the presence of specific biochemical factors involved in their adhesion: aggregation substances (Aggs) and the enterococcal surface protein (encoded by theespgene). In addition, physico-chemical factors involved in adhesion (zeta potential and cell surface hydrophobicity) were determined, as well as the influence of ox bile on these properties. Two-thirds of the biliary stent isolates displayed culture heterogeneity in the pH dependence of their zeta potentials. Moreover, 24 out of 46 clinical isolates ofE. faecalis, including 11 laboratory strains, also displayed such heterogeneity. The culture heterogeneity was demonstrated to be a stable trait, not caused by quorum sensing, not plasmid mediated, and independent of the presence ofespand Agg. Data presented show that culture heterogeneity in zeta potential enhances adhesion to an abiotic surface. A higher prevalence of culture heterogeneity in zeta potential in pathogenic as compared to non-pathogenic isolates could indicate that this phenomenon might play a role in virulence and putatively in pathogenesis.

Influence of fermentation medium composition on physicochemical surface properties of Lactobacillus acidophilus

The effect of the simple and complex basic components of a fermentation medium on the surface properties of Lactobacillus acidophilus NCC2628 is studied by physicochemical methods, such as electrophoresis, interfacial adhesion, and X-ray photonelectron spectroscopy, and by transmission electron microscopy. Starting from an optimized complete medium, the effect of carbohydrates, peptones, and yeast extracts on the physicochemical properties of the cell wall is systematically investigated by consecutively omitting one of the principal components from the fermentation medium at the time. The physicochemical properties and structure of the bacterial cell wall remain largely unchanged if the carbohydrate content of the fermentation medium is strongly reduced, although the concentration of surface proteins increases slightly. Both peptone and yeast extract have a considerable influence on the bacterial cell wall, as witnessed by changes in surface charge, hydrophobicity, and the nitrogen-to-carbon ratio. Both zeta potential and the cell wall hydrophobicity show a positive correlation with the nitrogen-to-carbon ratio of the bacterial surfaces, indicative of the important role of surface proteins in the overall surface physical chemistry. The hydrophobicity of the cell wall, which is low for the cultures grown in the complete medium and in the absence of carbohydrates, becomes fairly high for the cultures grown in the medium without peptones and the medium without yeast extract. UV spectrophotometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis combined with liquid chromatography-tandem mass spectrometry are used to analyze the effect of medium composition on LiCl-extractable cell wall proteins, confirming the major change in protein composition of the cell wall for the culture fermented in the medium without peptones. In particular, it is found that expression of the S-layer protein is dependent on the protein source of the fermentation medium.

The interaction between bacteria and bile

Commensal and pathogenic microorganisms must resist the deleterious actions of bile in order to survive in the human gastrointestinal tract. Herein we review the current knowledge on the mechanisms by which Gram-positive and Gram-negative bacteria contend with bile stress. We describe the antimicrobial actions of bile, assess the variations in bile tolerance between bacterial genera and examine the interplay between bile stress and other stresses. The molecular mechanisms underlying bile tolerance are investigated and the relationship between bile and virulence is examined. Finally, the potential benefits of bile research are briefly discussed.