First two domains at the lp_1643 protein N terminus inhibit pathogen adhesion to porcine mucus in vitro

Probiotics, mechanisms of action, and clinical perspectives for diarrhea management in children

Infectious diarrhea is the second most common cause of morbidity and mortality in children under 5 years of age in the underdeveloped areas of the world. Conventional treatment consists of rehydration, which may be coupled with antimicrobial agents in more severe bacterial infections or with antiprotozoal agents. In the last few decades, research on the use of probiotic strains, such as Lactobacillus rhamnosus GG ATCC 53013 (LGG), Lactobacillus reuteri DSM 17938 and Saccharomyces boulardii, has gained much attention to prevent and treat diarrheal diseases. However, they are rarely used in the clinical routine, perhaps because there are still gaps in the knowledge about the effective benefit to the patient in terms of the reduction of the duration of diarrhea and its prevention. Furthermore, only a few probiotic strains are safely indicated for usage in pediatric practice. This review summarizes the current knowledge on the antimicrobial mechanisms of probiotics on distinct enteropathogens and their role in stimulating host defense mechanisms against intestinal infections. In addition, we highlight the potential of probiotics for the treatment and prevention of diarrhea in children. We conclude that the use of probiotics is beneficial for both the treatment and prevention of diarrhea in children and that the identification of other candidate probiotics might represent an important advance to a greater reduction in hospital stays and to prevent infectious diarrhea in a larger portion of this population.

Mechanistic insights into the host-microbe interaction and pathogen exclusion mediated by the Mucus-binding protein of Lactobacillus plantarum

Surface adhesins of pathogens and probiotics strains are implicated in mediating the binding of microbes to host. Mucus-binding protein (Mub) is unique to gut inhabiting lactic acid bacteria; however, the precise role of Mub proteins or its structural domains in host-microbial interaction is not well understood. Last two domains (Mubs5s6) of the six mucus-binding domains arranged in tandem at the C-terminus of the Lp_1643 protein of Lactobacillus plantarum was expressed in E. coli. Mubs5s6 showed binding with the rat intestinal mucus, pig gastric mucins and human intestinal tissues. Preincubation of Mubs5s6 with the Caco-2 and HT-29 cell lines inhibited the binding of pathogenic enterotoxigenic E. coli cells to the enterocytes by 68% and 81%, respectively. Pull-down assay suggested Mubs5s6 binding to the host mucosa components like cytokeratins, Hsp90 and Laminin. Mubs5s6 was predicted to possess calcium and glucose binding sites. Binding of Mubs5s6 with these ligands was also experimentally observed. These ligands are known to be associated with pathogenesis suggesting Mub might negotiate pathogens in multiple ways. To study the feasibility of Mubs5s6 delivery in the gut, it was encapsulated in chitosan-sodium tripolyphosphate microspheres with an efficiency of 65% and release up to 85% in near neutral pH zone over a period of 20 hours. Our results show that Mub plays an important role in the host-microbial cross-talk and possesses the potential for pathogen exclusion to a greater extent than mediated by L. plantarum cells. The functional and technological characteristics of Mubs5s6 make it suitable for breaking the host-pathogen interaction.

Role of cell surface composition and lysis in static biofilm formation by Lactobacillus plantarum WCFS1

Next to applications in fermentations, Lactobacillus plantarum is recognized as a food spoilage organism, and its dispersal from biofilms in food processing environments might be implicated in contamination or recontamination of food products. This study provides new insights into biofilm development by L. plantarum WCFS1 through comparative analysis of wild type and mutants affected in cell surface composition, including mutants deficient in the production of Sortase A involved in the covalent attachment of 27 predicted surface proteins to the cell wall peptidoglycan (ΔsrtA) and mutants deficient in the production of capsular polysaccharides (CPS1-4, Δcps1-4). Surface adhesion and biofilm formation studies revealed none of the imposed cell surface modifications to affect the initial attachment of cells to polystyrene while biofilm formation based on Crystal Violet (CV) staining was severely reduced in the ΔsrtA mutant and significantly increased in mutants lacking the cps1 cluster, compared to the wild-type strain. Fluorescence microscopy analysis of biofilm samples pointed to a higher presence of extracellular DNA (eDNA) in cps1 mutants and this corresponded with increased autolysis activity. Subsequent studies using Δacm2 and ΔlytA derivatives affected in lytic behaviour revealed reduced biofilm formation measured by CV staining, confirming the relevance of lysis for the build-up of the biofilm matrix with eDNA.

Expression of fibronectin-binding protein of L. acidophilus NCFM and in vitro refolding to adhesion capable native-like protein from inclusion bodies

The ability of Lactobacilli to adhere to host epithelial surface and intestinal tracts is important for colonization and persistence of bacteria in the host gut. Extracellular matrix components like fibronectin, mucin, collagen and other adhesion molecules serve as substratum for attachment of bacteria. However, the precise structure, function and mechanism of binding of microbial surface adhesion proteins such as Fibronectin-binding protein (FBP) with host molecules remains unclear. This is primarily due to limitations in high expression of these proteins in biologically active form. To study adhesion of its FBP (64 kDa), the fbp gene of L. acidophilus NCFM was cloned and expressed in E. coli. However, the fibronectin-binding protein expressed in soluble form could not be purified by Ni-NTA affinity chromatography possibly because of partially buried Histidine tag in the recombinant fusion protein. Therefore, the protein was expressed as inclusion bodies (IBs) at 37 °C and solubilized in urea followed by purification in denatured form by Ni-NTA affinity chromatography. The purified denatured protein was refolded in vitro to structurally stable and biologically active form. The conformational properties of the refolded protein were studied by circular dichroism, which showed prominence of α+ β structural element. The refolded FBP also showed significant binding to human intestinal tissue sections. Our optimized refolding protocol from IBs of this recombinant probiotic FBP led into high amounts of biologically active protein. Our results help in increasing understanding of structure-function relation of surface adhesion proteins and host-microbial interactions.