Bacterial surface (S) layers are the outermost proteinaceous cell envelope structures found on members of nearly all taxonomic groups of bacteria and Archaea. They are composed of numerous identical subunits forming a symmetric, porous, lattice-like layer that completely covers the cell surface. The subunits are held together and attached to cell wall carbohydrates by non-covalent interactions, and they spontaneously reassemble in vitro by an entropy-driven process. Due to the low amino acid sequence similarity among S-layer proteins in general, verification of the presence of an S-layer on the bacterial cell surface usually requires electron microscopy. In lactobacilli, S-layer proteins have been detected on many but not all species. Lactobacillus S-layer proteins differ from those of other bacteria in their smaller size and high predicted pI. The positive charge in Lactobacillus S-layer proteins is concentrated in the more conserved cell wall binding domain, which can be either N- or C-terminal depending on the species. The more variable domain is responsible for the self-assembly of the monomers to a periodic structure. The biological functions of Lactobacillus S-layer proteins are poorly understood, but in some species S-layer proteins mediate bacterial adherence to host cells or extracellular matrix proteins or have protective or enzymatic functions. Lactobacillus S-layer proteins show potential for use as antigen carriers in live oral vaccine design because of their adhesive and immunomodulatory properties and the general non-pathogenicity of the species.

Recent research suggests that the microbial colonization of the mammalian intestine may begin before birth, but the observations are controversial due to challenges in the reliable sampling and analysis of low-abundance microbiota. We studied the perinatal microbiota of calves by sampling them immediately at birth and during the first postnatal week. The large size of the bovine newborns allows sampling directly from rectum using contamination-shielded swabs. Our 16S rDNA data, purged of potential contaminant sequences shared with negative controls, indicates the existence of a diverse low-abundance microbiota in the newborn rectal meconium and mucosa. The newborn rectal microbiota was composed of Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes. The microbial profile resembled dam oral rather than fecal or vaginal vestibular microbiota, but included typical intestinal taxa. During the first postnatal day, the rectum was invaded byEscherichia/ShigellaandClostridia, and the diversity collapsed. By 7 days, diversity was again increasing. In terms of relative abundance, Proteobacteria were replaced by Firmicutes, Bacteroidetes and Actinobacteria, includingFaecalibacterium,Bacteroides,Lactobacillus,ButyricicoccusandBifidobacterium. Our observations suggest that mammals are seeded before birth with a diverse microbiota, but the microbiota changes rapidly in the early postnatal life.

Depletion of the SlpA protein from the bacterial surface greatly reduced the adhesion of Lactobacillus brevis ATCC 8287 to the human intestinal cell lines Caco-2 and Intestine 407, the endothelial cell line EA-hy926, and the urinary bladder cell line T24, as well as immobilized fibronectin. For functional analysis of the SlpA surface protein, different regions of the slpA gene were expressed as internal in-frame fusions in the variable region of the fliC _H7 gene of Escherichia coli . The resulting chimeric flagella carried inserts up to 275 amino acids long from the mature S-layer protein, which is 435 amino acids in size. The expression of the SlpA fragments on the chimeric flagella was assessed by immunoelectron microscopy and Western blotting using anti-SlpA antibodies, and their binding to human cells was assessed by indirect immunofluorescence. Chimeric flagella harboring inserts that represented the N-terminal part of the S-layer protein bound to the epithelial cell lines, whereas the C-terminal part of the S-layer protein did not confer binding on the flagella. The shortest S-layer peptide capable of detectable binding was 81 amino acid residues in size and represented residues 96 through 176 in the unprocessed S-layer protein. The bacteria and the chimeric flagella did not show detectable binding to erythrocytes, whereas the SlpA-expressing ATCC 8287 cells as well as the chimeric SlpA 96-245/FliC flagella bound to immobilized fibronectin. The N-terminal SlpA peptide 96-176 or 96-200 fused to FliC was not recognized in Western blotting or immunoelectron microscopy by a polyclonal serum raised against the S-layer protein; the antiserum, however, reacted in immunofluorescence with the ATCC 8287 cells. In contrast, an antiserum raised against the His-tagged peptide 96-245 of SlpA bound to the hybrid flagella with the N-terminal SlpA inserts but did not react with ATCC 8287 cells. The results identify the S-layer of L. brevis ATCC 8287 as an adhesin with affinity for human epithelial cells and fibronectin and locate the receptor-binding region within a fragment of 81 amino acids in the N-terminal part of the molecule, which in native S-layer seems inaccessible to antibodies.

Background: Lactobacillus brevis ATCC 8287 is covered by a regular surface (S-) layer consisting of a 435 amino acid protein SlpA. This protein is completely unrelated in sequence to the previously characterized S-layer proteins of Lactobacillus acidophilus group. Results: In this work, the self-assembly and cell wall binding domains of SlpA were characterized. The C-terminal self-assembly domain encompassed residues 179–435 of mature SlpA, as demonstrated by the ability of N-terminally truncated recombinant SlpA to form a periodic structure indistinguishable from that formed by full length SlpA. Furthermore, a trypsin degradation analysis indicated the existence of a protease resistant C-terminal domain of 214 amino acids. By producing a set of C-terminally truncated recombinant SlpA (rSlpA) proteins the cell wall binding region was mapped to the N-terminal part of SlpA, where the first 145 amino acids of mature SlpA alone were sufficient for binding to isolated cell wall fragments of L. brevis ATCC 8287. The binding of full length rSlpA to the cell walls was not affected by the treatment of the walls with 5% trichloroacetic acid (TCA), indicating that cell wall structures other than teichoic acids are involved, a feature not shared by the Lactobacillus acidophilus group S-layer proteins characterized so far. Conserved carbohydrate binding motifs were identified in the positively charged N-terminal regions of six Lactobacillus brevis S-layer proteins. Conclusion: This study identifies SlpA as a two-domain protein in which the order of the functional domains is reversed compared to other characterized Lactobacillus S-layer proteins, and emphasizes the diversity of potential cell wall receptors despite similar carbohydrate binding sequence motifs in Lactobacillus S-layer proteins.

Infected superficial wounds were traditionally controlled by topical antibiotics until the emergence of antibiotic-resistant bacteria. Silver (Ag) is a kernel for alternative antibacterial agents to fight this resistance quandary. The present study demonstrates a method for immobilizing small-sized (~5 nm) silver nanoparticles on silica matrix to form a nanosilver–silica (Ag–SiO₂) composite and shows the prolonged antibacterial effects of the composite in vitro. The composite exhibited a rapid initial Ag release after 24 h and a slower leaching after 48 and 72 h and was effective against both methicillin-resistant Staphylococcus aureus (MRSA) and Escherichia coli (E. coli). Ultraviolet (UV)-irradiation was superior to filter-sterilization in retaining the antibacterial effects of the composite, through the higher remaining Ag concentration. A gauze, impregnated with the Ag–SiO₂ composite, showed higher antibacterial effects against MRSA and E. coli than a commercial Ag-containing dressing, indicating a potential for the management and infection control of superficial wounds. Transmission and scanning transmission electron microscope analyses of the composite-treated MRSA revealed an interaction of the released silver ions with the bacterial cytoplasmic constituents, causing ultimately the loss of bacterial membranes. The present results indicate that the Ag–SiO₂ composite, with prolonged antibacterial effects, is a promising candidate for wound dressing applications.

Adhesiveness to intestinal epithelium, beneficial immunomodulating effects and the production of pathogen-inhibitory compounds are generally considered as beneficial characteristics of probiotic organisms. We showed the potential health-promoting properties and the mechanisms of probiotic action of seven swine intestinal Lactobacillus amylovorus isolates plus the type strain (DSM 20531T) by investigating their adherence to porcine intestinal epithelial cells (IPEC-1) and mucus as well as the capacities of the strains to i) inhibit the adherence of Escherichia coli to IPEC-1 cells, ii) to produce soluble inhibitors against intestinal pathogens and iii) to induce immune signaling in dendritic cells (DCs). Moreover, the role of the L. amylovorus surface (S) –layers - symmetric, porous arrays of identical protein subunits present as the outermost layer of the cell envelope - in adherence to IPEC-1 cells was assessed using a novel approach which utilized purified cell wall fragments of the strains as carriers for the recombinantly produced S-layer proteins.