Importance of S-layer proteins in probiotic activity of Lactobacillus acidophilus M92

Diversity in S-layers

Surface layers, referred simply as S-layers, are the two-dimensional crystalline arrays of protein or glycoprotein subunits on cell surface. They are one of the most common outermost envelope components observed in prokaryotic organisms (Archaea and Bacteria). Over the past decades, S-layers have become an issue of increasing interest due to their ubiquitousness, special features and functions. Substantial work in this field provides evidences of an enormous diversity in S-layers. This paper reviews and illustrates the diversity from several different aspects, involving the S-layer-carrying strains, the structure of S-layers, the S-layer proteins and genes, as well as the functions of S-layers.

Conserved S-Layer-Associated Proteins Revealed by Exoproteomic Survey of S-Layer-Forming Lactobacilli

The Lactobacillus acidophilus homology group comprises Gram-positive species that include L. acidophilus, L. helveticus, L. crispatus, L. amylovorus, L. gallinarum, L. delbrueckii subsp. bulgaricus, L. gasseri, and L. johnsonii. While these bacteria are closely related, they have varied ecological lifestyles as dairy and food fermenters, allochthonous probiotics, or autochthonous commensals of the host gastrointestinal tract. Bacterial cell surface components play a critical role in the molecular dialogue between bacteria and interaction signaling with the intestinal mucosa. Notably, the L. acidophilus complex is distinguished in two clades by the presence or absence of S-layers, which are semiporous crystalline arrays of self-assembling proteinaceous subunits found as the outermost layer of the bacterial cell wall. In this study, S-layer-associated proteins (SLAPs) in the exoproteomes of various S-layer-forming Lactobacillus species were proteomically identified, genomically compared, and transcriptionally analyzed. Four gene regions encoding six putative SLAPs were conserved in the S-layer-forming Lactobacillus species but not identified in the extracts of the closely related progenitor, L. delbrueckii subsp. bulgaricus, which does not produce an S-layer. Therefore, the presence or absence of an S-layer has a clear impact on the exoproteomic composition of Lactobacillus species. This proteomic complexity and differences in the cell surface properties between S-layer- and non-S-layer-forming lactobacilli reveal the potential for SLAPs to mediate intimate probiotic interactions and signaling with the host intestinal mucosa.

Effects of sub-lethal high-pressure homogenization treatment on the outermost cellular structures and the volatile-molecule profiles of two strains of probiotic lactobacilli

Applying sub-lethal levels of high-pressure homogenization (HPH) to lactic acid bacteria has been proposed as a method of enhancing some of their functional properties. Because the principal targets of HPH are the cell-surface structures, the aim of this study was to examine the effect of sub-lethal HPH treatment on the outermost cellular structures and the proteomic profiles of two known probiotic bacterial strains. Moreover, the effect of HPH treatment on the metabolism of probiotic cells within a dairy product during its refrigerated storage was investigated using SPME-GC-MS. Transmission electron microscopy was used to examine the microstructural changes in the outermost cellular structures due to HPH treatment. These alterations may be involved in the changes in some of the technological and functional properties of the strains that were observed after pressure treatment. Moreover, the proteomic profiles of the probiotic strains treated with HPH and incubated at 37°C for various periods showed different peptide patterns compared with those of the untreated cells. In addition, there were differences in the peaks that were observed in the low-mass spectral region (2000–3000 Da) of the spectral profiles of the control and treated samples. Due to pressure treatment, the volatile-molecule profiles of buttermilk inoculated with treated or control cells and stored at 4°C for 30 days exhibited overall changes in the aroma profile and in the production of molecules that improved its sensory profile, although the two different species imparted specific fingerprints to the product. The results of this study will contribute to understanding the changes that occur in the outermost cellular structures and the metabolism of LAB in response to HPH treatment. The findings of this investigation may contribute to elucidating the relationships between these changes and the alterations of the technological and functional properties of LAB induced by pressure treatment.

Lactobacillus reuteri glyceraldehyde-3-phosphate dehydrogenase functions in adhesion to intestinal epithelial cells

This study was aimed to identify key surface proteins mediating the adhesion of lactobacilli to intestinal epithelial cells. By using Caco-2 and IPEC-J2 cells labeled with sulfo-NHS-biotin in the western blotting, a protein band of an approximately 37 kDa was detected on the surface layer of Lactobacillus reuteri strains ZJ616, ZJ617, ZJ621, and ZJ623 and Lactobacillus rhamnosus GG. Mass spectrometry analysis using the adhesion-related protein from L. reuteri ZJ617 showed that it was 100% homologous to the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) of L. reuteri JCM 1112 (GenBank: YP_001841377). The ability of L. reuteri ZJ617 to adhere to epithelial cells decreased significantly by treatment with LiCl or by blocking with an anti-GAPDH antibody, in comparison with the untreated strain (p < 0.05). Immunoelectron microscopic and immunofluorescence analyses confirmed that GAPDH is located on the surface layer of L. reuteri ZJ617. The results indicated that the GAPDH protein of L. reuteri ZJ617 acts as an adhesion component that plays an important role in binding to the intestinal epithelial cells.

The Differential Proteome of the Probiotic Lactobacillus acidophilus NCFM Grown on the Potential Prebiotic Cellobiose Shows Upregulation of Two β -Glycoside Hydrolases

Probiotics, prebiotics, and combinations thereof, that is, synbiotics, are known to exert beneficial health effects in humans; however interactions between pro- and prebiotics remain poorly understood at the molecular level. The present study describes changes in abundance of different proteins of the probiotic bacterium Lactobacillus acidophilus NCFM (NCFM) when grown on the potential prebiotic cellobiose as compared to glucose. Cytosolic cell extract proteomes after harvest at late exponential phase of NCFM grown on cellobiose or glucose were analyzed by two dimensional difference gel electrophoresis (2D-DIGE) in the acidic (pH 4-7) and the alkaline (pH 6-11) regions showing a total of 136 spots to change in abundance. Proteins were identified by MS or MS/MS from 81 of these spots representing 49 unique proteins and either increasing 1.5-13.9-fold or decreasing 1.5-7.8-fold in relative abundance. Many of these proteins were associated with energy metabolism, including the cellobiose related glycoside hydrolases phospho-β-glucosidase (LBA0881) and phospho-β-galactosidase II (LBA0726). The data provide insight into the utilization of the candidate prebiotic cellobiose by the probiotic bacterium NCFM. Several of the upregulated or downregulated identified proteins associated with utilization of cellobiose indicate the presence of carbon catabolite repression and regulation of enzymes involved in carbohydrate metabolism.

Role of S-layer proteins in the biosorption capacity of lead by Lactobacillus kefir

The role of S-layer proteins (SLP) on the Pb(2+) sequestrant capacity by Lactobacillus kefir CIDCA 8348 and JCM 5818 was investigated. Cultures in the stationary phase were treated with proteinase K. A dot blot assay was carried out to assess the removal of SLP. Strains with and without SLP were exposed to 0-0.5 mM Pb(NO3)2. The maximum binding capacity (q max ) and the affinity coefficient (b) were calculated using the Langmuir equation. The structural effect of Pb(2+) on microorganisms with and without SLP was determined using Raman spectroscopy. The bacterial interaction with Pb(2+) led to a broadening in the phosphate bands (1,300-1,200 cm(-1) region) and strong alterations on amide and carboxylate-related bands (νCOO(-) as and νCOO(-) s). Microorganisms without SLP removed higher percentages of Pb(2+) and had higher q max than those bearing SLP. Isolated SLP had much lower q max and also removed lower percentages of Pb(2+) than the corresponding whole microorganisms. The hydrofobicity of both strains dramatically dropped when removing SLP. When bearing SLP, strains do not expose a large amount of charged groups on their surfaces, thus making less efficient the Pb(2+) removal. On the contrary, the extremely low hydrofobicity of microorganisms without SLP (and consequently, their higher capacity to remove Pb(2+)) can be explained on the basis of a greater exposure of charged chemical groups for the interaction with Pb(2+). The viability of bacteria without SLP was not significantly lower than that of bacteria bearing SLP. However, microorganisms without SLP were more prone to the detrimental effect of Pb(2+), thus suggesting that SLP acts as a protective rather than as a sequestrant layer.

Sortase-deficient lactobacilli: effect on immunomodulation and gut retention

Surface proteins of probiotic microbes, including Lactobacillus acidophilus and Lactobacillus gasseri, are believed to promote retention in the gut and mediate host-bacterial communications. Sortase, an enzyme that covalently couples a subset of extracellular proteins containing an LPXTG motif to the cell surface, is of particular interest in characterizing bacterial adherence and communication with the mucosal immune system. A sortase gene, srtA, was identified in L. acidophilus NCFM (LBA1244) and L. gasseri ATCC 33323 (LGAS_0825). Additionally, eight and six intact sortase-dependent proteins were predicted in L. acidophilus and L. gasseri, respectively. Due to the role of sortase in coupling these proteins to the cell wall, ΔsrtA deletion mutants of L. acidophilus and L. gasseri were created using the upp-based counterselective gene replacement system. Inactivation of sortase did not cause significant alteration in growth or survival in simulated gastrointestinal juices. Meanwhile, both ΔsrtA mutants showed decreased adhesion to porcine mucin in vitro. Murine dendritic cells exposed to the ΔsrtA mutant of L. acidophilus or L. gasseri induced lower levels of pro-inflammatory cytokines TNF-α and IL-12, respectively, compared with the parent strains. In vivo co-colonization of the L. acidophilus ΔsrtA mutant and its parent strain in germ-free 129S6/SvEv mice resulted in a significant one-log reduction of the ΔsrtA mutant population. Additionally, a similar reduction of the ΔsrtA mutant was observed in the caecum. This study shows for the first time that sortase-dependent proteins contribute to gut retention of probiotic microbes in the gastrointestinal tract.

Activity of lysozyme on Lactobacillus hilgardii strains isolated from Port wine

This work evaluated the effect of lysozyme on lactobacilli isolated from Port wine. Bacterial growth experiments were conducted in MRS/TJ medium and inactivation studies were performed in phosphate buffer (KH2PO4), distilled water and wine supplemented with different concentrations of lysozyme. The response of bacteria to lysozyme was found to be highly strain dependent. Some strains of Lactobacillus hilgardii together with Lactobacillus collinoides and Lactobacillus fructivorans were found to be resistant to concentrations of lysozyme as high as 2000 mg/L. It was observed that among the L. hilgardii taxon the resistant strains possess an S-layer coat. Apparently, the strains of L. collinoides and L. fructivorans studied are also S-layer producers as suggested by the total protein profile obtained by SDS-PAGE. Thus, the hypothetical protective role of the S-layer against the action of lysozyme was investigated. From the various treatments used to remove the protein from the surface of the cells, the one employing LiCl (5 M) was the most effective. LiCl pre-treated cells exposed to lysozyme (2000 mg/L) in KH2PO4 buffer maintained its resistance. However, when cells were suspended in distilled water an increased sensitivity to lysozyme was observed. Moreover, it was found that the addition of ethanol (20% v/v) to the suspension medium (distilled water) triggered a strong inactivation effect especially on cells previously treated with LiCl (reduction of >6 CFU log cycles). The results suggest that the S-layer exerts a protective effect against lysozyme and that the cell suspension medium influences the bacteriolysis efficiency. It was also noted that ethanol enhances the inactivation effect of lysozyme.

Variability of S-layer proteins in Lactobacillus helveticus strains

The presence of S-layer proteins in the cell envelope of Lactobacillus helveticus may be technologically important. S-layer proteins are the adhesion site for cell envelope proteinase, which forms the proteolytic pathway in bacteria. Eleven strains of L. helveticus were examined for the presence of S-layer proteins and slpH genes. S-layer proteins from six strains were identified and sequenced. Multiple alignments of the deduced amino acid sequences demonstrated a strong sequence conservation of all Slp studied. Transmission Electron Microscopy analysis of the cells revealed the typical cell wall architecture of the S-layer. This is the first report on characterisation of glycosylated S-layer proteins from different strains of L. helveticus. The amino acid composition, the secondary structure, and the physical properties of these proteins were found to be quite similar to those of S-layer proteins from other lactobacilli. However, PCR analysis revealed that five of the examined strains of L. helveticus did not have slpH genes. This finding suggests that S-layer protein genes cannot be considered as housekeeping genes and cannot be used as molecular markers for L. helveticus.

Adhesion properties of potentially probiotic Lactobacillus kefiri to gastrointestinal mucus

We investigated the mucus-binding properties of aggregating and non-aggregating potentially probiotic strains of kefir-isolated Lactobacillus kefiri, using different substrates. All the strains were able to adhere to commercial gastric mucin (MUCIN) and extracted mucus from small intestine (SIM) and colon (CM). The extraction of surface proteins from bacteria using LiCl or NaOH significantly reduced the adhesion of three selected strains (CIDCA 8348, CIDCA 83115 and JCM 5818); although a significant proportion (up to 50%) of S-layer proteins were not completely eliminated after treatments. The surface (S-layer) protein extracts from all the strains of Lb. kefiri were capable of binding to MUCIN, SIM or CM, and no differences were observed among them. The addition of their own surface protein extract increased adhesion of CIDCA 8348 and 83115 to MUCIN and SIM, meanwhile no changes in adhesion were observed for JCM 5818. None of the seven sugars tested had the ability to inhibit the adhesion of whole bacteria to the three mucus extracts. Noteworthy, the degree of bacterial adhesion reached in the presence of their own surface protein (S-layer) extract decreased to basal levels in the presence of some sugars, suggesting an interaction between the added sugar and the surface proteins. In conclusion, the ability of these food-isolated bacteria to adhere to gastrointestinal mucus becomes an essential issue regarding the biotechnological potentiality of Lb. kefiri for the food industry.

Identification of extracellular surface-layer associated proteins in Lactobacillus acidophilus NCFM

Bacterial surface (S-) layers are crystalline arrays of self-assembling, proteinaceous subunits called S-layer proteins (Slps), with molecular masses ranging from 40 to 200 kDa. The S-layer-forming bacterium Lactobacillus acidophilus NCFM expresses three major Slps: SlpA (46 kDa), SlpB (47 kDa) and SlpX (51 kDa). SlpA has a demonstrated role in adhesion to Caco-2 intestinal epithelial cells in vitro, and has been shown to modulate dendritic cell (DC) and T-cell functionalities with murine DCs. In this study, a modification of a standard lithium chloride S-layer extraction revealed 37 proteins were solubilized from the S-layer wash fraction. Of these, 30 have predicted cleavage sites for secretion, 24 are predicted to be extracellular, six are lipid-anchored, three have N-terminal hydrophobic membrane spanning regions and four are intracellular, potentially moonlighting proteins. Some of these proteins, designated S-layer associated proteins (SLAPs), may be loosely associated with or embedded within the bacterial S-layer complex. Lba-1029, a putative SLAP gene, was deleted from the chromosome of L. acidophilus. Phenotypic characterization of the deletion mutant demonstrated that the SLAP LBA1029 contributes to a pro-inflammatory TNF-α response from murine DCs. This study identified extracellular proteins and putative SLAPs of L. acidophilus NCFM using LC-MS/MS. SLAPs appear to impart important surface display features and immunological properties to microbes that are coated by S-layers.

A functional glycogen biosynthesis pathway in Lactobacillus acidophilus: expression and analysis of the glg operon

Glycogen metabolism contributes to energy storage and various physiological functions in some prokaryotes, including colonization persistence. A role for glycogen metabolism is proposed on the survival and fitness of Lactobacillus acidophilus, a probiotic microbe, in the human gastrointestinal environment. L. acidophilus NCFM possesses a glycogen metabolism (glg) operon consisting of glgBCDAP-amy-pgm genes. Expression of the glg operon and glycogen accumulation were carbon source- and growth phase-dependent, and were repressed by glucose. The highest intracellular glycogen content was observed in early log-phase cells grown on trehalose, which was followed by a drastic decrease of glycogen content prior to entering stationary phase. In raffinose-grown cells, however, glycogen accumulation gradually declined following early log phase and was maintained at stable levels throughout stationary phase. Raffinose also induced an overall higher temporal glg expression throughout growth compared with trehalose. Isogenic ΔglgA (glycogen synthase) and ΔglgB (glycogen-branching enzyme) mutants are glycogen-deficient and exhibited growth defects on raffinose. The latter observation suggests a reciprocal relationship between glycogen synthesis and raffinose metabolism. Deletion of glgB or glgP (glycogen phosphorylase) resulted in defective growth and increased bile sensitivity. The data indicate that glycogen metabolism is involved in growth maintenance, bile tolerance and complex carbohydrate utilization in L. acidophilus.

Strain-specific detection of orally administered canine jejunum-dominated Lactobacillus acidophilus LAB20 in dog faeces by real-time PCR targeted to the novel surface layer protein

Lactobacillus acidophilus LAB20 has potential to be a probiotic strain because it can be present at high numbers in the jejunum of dog. To specifically detect LAB20 from dog faecal samples, a real-time PCR protocol was developed targeting the novel surface (S) layer protein gene of LAB20. The presence of S-layer protein was verified by N-terminal sequencing of the approximately 50-kDa major band from SDS-PAGE gel. The corresponding S-layer gene was amplified by inverse PCR using homology to known S-layers and sequenced. This novel S-layer protein has low sequence similarity to other S-layer proteins in the N-terminal region (32-211 aa, 7-39%). This enabled designing strain-specific PCR primers. The primer set was utilized to study intestinal persistence of LAB20 in dog that was fed with LAB20 fermented milk for 5 days. The results showed that LAB20 can be detected from dog faecal sample after 6 weeks with 10(4·53)  DNA copies g(-1) postadministration. It suggested that LAB20 could be a good candidate to study the mechanism behind its persistence and dominance in dog intestine and maybe utilize it as a probiotic for canine.

SIGNIFICANCE AND IMPACT OF THE STUDY

A real-time PCR method was developed to detect Lactobacillus acidophilus LAB20, a strain that was previously found dominant in canine gastrointestinal (GI) tract. The quantitative detection was based on targeting to variation region of a novel S-layer protein found in LAB20, allowing to specifically enumerate LAB20 from dog faeces. The results showed that the real-time PCR method was sensitive enough to be used in later intervention studies. Interestingly, LAB20 was found to persist in dog GI tract for 6 weeks. Therefore, LAB20 could be a good candidate to study its colonization and potentially utilize as a canine probiotic.

Adhesive ability means inhibition activities for lactobacillus against pathogens and S-layer protein plays an important role in adhesion

Eighty-five strains of lactobacillus were isolated from the pig intestine and identified by sequencing analysis based on 16S rRNA gene, from which five lactobacillus strains with high adhesive ability were selected. The inhibition ability of the five lactobacillus strains with or without S-layer proteins against adherence of Escherichia coli K88 and Salmonella enteritidis 50335 to Caco-2 was evaluated in vitro with Lactobacillus rhamnosus GG strain (LGG) as a positive control. In addition, tolerance of lactobacilli to heat, acid, bile, Zn(2+) and Cu(2+) were assessed. All five selected strains, Lactobacillus salivarius ZJ614 (JN981856), Lactobacillus reuteri ZJ616 (JN981858), L. reuteri ZJ617 (JN981859), L. reuteri ZJ621 (JN981863) and L. reuteri ZJ623 (JN981865), showed inhibition against the two pathogens, E. coli K88 and S. enteritidis 50335. L. reuteri ZJ621 showed higher inhibition ability than the others to S. enteritidis 50335 (P < 0.05). Sodium dodecyl sulfate-Polyacrylamide gel electrophoresis (SDS-PAGE) analysis indicated that all five strains had abundant bands with molecular weight ranging from 34 to 130 KDa as well as had a common band of approximately 42 KDa. After treatment with 5 M LiCl to remove S-layer protein, the inhibition activities of the lactobacilli against pathogens decreased significantly (P < 0.05). The results showed that higher adhesive ability means higher inhibition activity for lactobacillus against pathogen, in which S-layer proteins plays an important role.

Lactobacillus surface layer proteins: structure, function and applications

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.

Proteolytic activity of probiotic strain Lactobacillus helveticus M92

The aim of this research was to investigate the potential of previously defined probiotic strain Lactobacillus helveticus M92 as functional starter culture for fermented dairy products. Therefore, proteolytic activity of L. helveticus M92 was investigated and compared with those of different representatives of probiotic and starter culture strains. Cluster analysis of AFLP fingerprints showed a difference of L. helveticus M92 compared to five other L. helveticus strains, but the percentage of similarity confirmed the identification on species level. Casein hydrolysis by L. helveticus M92 was monitored by agar-well diffusion test, SDS-PAGE and Anson's method. L. helveticus M92 exhibited the highest proteolytic activity among tested probiotic and starter cultures strains with the fastest acidification rate and the highest pH decrease after overnight incubation in skim milk. The presence of prtH2 gene was confirmed by PCR amplification with specific primers, while PCR product was not obtained after amplification with primers specific to prtH. Furthermore, SDS-PAGE LC-MS/MS analysis of insoluble proteome of L. helveticus M92 enabled identification of several proteins involved in proteolytic system of L. helveticus such as protease PrtM as well as proteins involved in Opp peptide transport system and the intracellular peptidases PepE, PepN, and PepQ.

S-layer protein mediates the stimulatory effect of Lactobacillus helveticus MIMLh5 on innate immunity

The ability to positively affect host health through the modulation of the immune response is a feature of increasing importance in measuring the probiotic potential of a bacterial strain. However, the identities of the bacterial cell components involved in cross talk with immune cells remain elusive. In this study, we characterized the dairy strain Lactobacillus helveticus MIMLh5 and its surface-layer protein (SlpA) using in vitro and ex vivo analyses. We found that MIMLh5 and SlpA exert anti-inflammatory effects by reducing the activation of NF-κB on the intestinal epithelial Caco-2 cell line. On the contrary, MIMLh5 and SlpA act as stimulators of the innate immune system by triggering the expression of proinflammatory factors tumor necrosis factor alpha and COX-2 in the human macrophage cell line U937 via recognition through Toll-like receptor 2. In the same experiments, SlpA protein did not affect the expression of the anti-inflammatory cytokine interleukin-10. A similar response was observed following stimulation of macrophages isolated from mouse bone marrow or the peritoneal cavity. These results suggest that SlpA plays a major role in mediating bacterial immune-stimulating activity, which could help to induce the host's defenses against and responses toward infections. This study supports the concept that the viability of bacterial cells is not always essential to exert immunomodulatory effects, thus permitting the development of safer therapies for the treatment of specific diseases according to a paraprobiotic intervention.

Histological examination of non-lactating bovine udders inoculated with Lactobacillus perolens CRL 1724

The effect of intramammary inoculation of Lactobacillus perolens CRL 1724 on bovine udders at drying off was evaluated through histological examination of the canal and cistern tissues. The persistence of the strain in the udder 7 d post inoculation was also determined. Lb. perolens CRL 1724 was recovered from all mammary quarters and no clinical signs or teat damage were observed after inoculation of 10(6) cfu/ml. The udders showed a normal structural aspect and there were no modifications of the milk appearance. Lb. perolens CRL 1724 cells were evidenced on the surface of the epithelial cells of the cistern without causing any morphological modifications or cell alterations. Lb. perolens CRL 1724 produces a mild inflammatory reaction, characterized by recruitment of neutrophils to the epithelial zone and a slight hyperaemia into blood vessels. This preliminary study provides important information for further studies directed towards the inclusion of Lb. perolens CRL 1724 in the design of probiotic products for preventing bovine mastitis in non-lactating dairy cows.

Screening of probiotic lactobacilli for inhibition of Shigella sonnei and the macromolecules involved in inhibition

A total of 91 lactobacilli were screened for antimicrobial activity against Shigella sonnei. Agar-well assay showed that 16 lactobacilli displayed strong antibacterial activity against S. sonnei. The nature of these antimicrobial agents were investigated and shown to be dependent on their production of organic acids. Adhesion tests showed that 6 lactobacilli demonstrated good adherence to HT-29 cells, of these Lactobacillus johnsonii F0421 were selected for acid and bile salt tolerance properties. We further research on L. johnsonii F0421 inhibition of S. sonnei adhesion to HT-29 cells. The result showed that L. johnsonii F0421 exhibited significant inhibitory activity and excluded, competed and displaced adhered S. sonnei by 48%, 38% and 33%, respectively. In order to elucidate the inhibitory functions of macromolecules involved in L. johnsonii F0421, the cells were treated with 5 M LiCl, 0.05 M sodium metaperiodate and heating and assayed for inhibition activity. The results suggested a role of S-layer proteins on L. johnsonii F0421 cells in inhibition of the adhesion process, but carbohydrates do not seem to be involved. SDS-PAGE analysis confirmed the presence of S-layer proteins with dominant bands of approximately 40 kDa. In addition, 100 μg/well of S-layer proteins from L. johnsonii F0421 cells were effective in inhibiting adhesion of S. sonnei to HT-29 cells. These findings suggest that L. johnsonii F0421 possesses the capacity for inhibition of S. sonnei activity as well as probiotic properties, which could serve as a potential novel and effective probiotic strain for use in the food industry.

S-layer proteins of Lactobacillus acidophilus inhibits JUNV infection

It has been previously described that S-layer binds to the C-type lectin DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN, CD209). It was also shown that DC-SIGN is a cell-surface adhesion factor that enhances viral entry of several virus families. Among those, Junin virus (JUNV) entry is enhanced in cells expressing DC-SIGN and for that reason surface-layer protein (S-layer) of Lactobacillus acidophilus ATCC 4365 was evaluated as a possible JUNV inhibitor. Experiments using 3T3 cells stably expressing DC-SIGN, showed an almost complete inhibition of JUNV infection when they were treated with S-layer in a similar extend as the inhibition shown by mannan. However no inhibition effect was observed in 3T3 wild type cells or in 3T3 cells expressing liver/lymph node-specific ICAM-3 grabbing nonintegrin (L-SIGN or DC-SIGNR or CD209L).

Treatments with S-layer during different times in the infection demonstrated that inhibition was only observed when S-layer was presented in early stages of the viral infection. This inhibition does not involve the classic recognition of mannose by this C-type lectin as the S-layer showed no evidence to be glycosylated. In fact, the highly basic nature of the S-layer (pI > 9.5) seems to be involved in electrostatic interactions between DC-SIGN and S-layer, since high pH abolished the inhibitory effect on infection cause by the S-layer. In silico analysis predicts a Ca²⁺-dependant carbohydrate recognition domain in the SlpA protein.

This novel characteristic of the S-layer, a GRAS status protein, contribute to the pathogen exclusion reported for this probiotic strain and may be applied as an antiviral agent to inhibit several kinds of viruses.

Effects of intramammary inoculation ofLactobacillus perolensCRL1724 in lactating cows’ udders

Bovine mastitis is the most important infectious disease on dairy farms. Conventional antibiotic therapy is often unsatisfactory and alternative treatments are continually under investigation.Lactobacillus (Lb.) perolensCRL 1724 andLactobacillus plantarumCRL 1716 were previously isolated from milk of dairy cows and selected according to their potential probiotic properties. In the present work the in-vitro capacity ofLactobacillusstrains to adhere to bovine teat canal epithelial cells (BTCEC) and to inhibit and co-aggregate 14 mastitis-causing pathogens (MCPs) was investigated. The effect ofLb. perolensCRL 1724 after intramammary inoculation in lactating cows was evaluated through determination of clinical signs of mastitis, milk appearance, somatic cell counts andLb. perolensCRL 1724 recovery from milk.Lb. perolensCRL 1724 was able to inhibit 12 of 14 MCPs (85·7%) in vitro, especially those considered to be major pathogens. In addition,Lb. perolensCRL 1724 co-aggregated with all of them.Lb. plantarumCRL 1716 was able to inhibit 7 of 14 MCPs (50%) in vitro and showed co-aggregation ability similar toLb. perolensCRL 1724.Lb. perolensCRL 1724 showed a higher efficacy of adhesion to BTCEC (values of percentage of adhesion and adhesion index of 75% and 14·4, respectively) thanLb. plantarumCRL 1716 (37% and 7·4, respectively).Lb. perolensCRL 1724 was recovered from all mammary quarters and no clinical signs or teat damage were observed after the inoculation of 106cfu/ml. The udders presented a normal aspect and there were no changes in the appearance of the milk. The results obtained will serve as the basis for further trials to evaluate the potential ofLb. perolensCRL 1724 to be included in a non-antibiotic formulation for the prevention of bovine mastitis.

Analysis of the Cell Surface Hydrophobicity of Yoghurt Fermentation Bacteria

The cell surface hydrophobicity (CSH) of lactic acid bacteria was considered to colonization and adhesion, and playing a prebiotic function in the digestive tract. Therefore, CSH of yoghurt fermentation bacteria most commonly used was analyzed, such as Lactobacillus acidophilus, Lactobacillus bulgaricus and Streptococcus thermophilus to identify initially CSH and the influencing factors of CSH of these strains and provided a theoretical basis for the future production of high-quality dairy fermentation agents and probiotics. The method of bacterial adhesion to hydrocarbons (BATH) was utilized to determine CSH of these strains and used the different conditions to process the cell. Through this research, the results was that L. acidophilus had a strong CSH, greater than L. bulgaricus and S. thermophilus. And the influencing factors of CSH of L. acidophilus were time, temperature, pH, concentration, Ca2+ and protease. But CSH was significantly reduced by trypsin and pepsin. CSH L. acidophilus was connected with the adhesion ability. In addition, it was speculated that some substances which could mediate CSH of L. acidophilus may be a class of proteins. Therefore, in the process of dairy fermentation agent, these factors could be controlled to obtain high-quality products.

Dissimilar properties of two recombinant Lactobacillus acidophilus strains displaying Salmonella FliC with different anchoring motifs

Display of heterologous antigens on the cell surface is considered a useful technique for vaccine delivery by recombinant lactobacilli. In this study, two recombinant Lactobacillus acidophilus derivatives displaying Salmonella flagellin (FliC) were constructed using different anchor motifs. In one instance, the FliC protein was fused to the C-terminal region of a cell envelope proteinase (PrtP) and was bound to the cell wall by electrostatic bonds. In the other case, the same antigen was conjugated to the anchor region of mucus binding protein (Mub) and was covalently associated with the cell wall by an LPXTG motif. These two recombinant L. acidophilus cell surface displays resulted in dissimilar maturation and cytokine production by human myeloid dendritic cells. The surface-associated antigen was highly sensitive to simulated gastric and small intestinal juices. By supplementation with bicarbonate buffer and soybean trypsin inhibitor, the cell surface antigen was protected from proteolytic enzymes during gastric challenge in vitro. The protective reagents also increased the viability of the L. acidophilus cells upon challenge with simulated digestive juices. These results demonstrate the importance of protecting cells and their surface-associated antigens during oral immunization.

Enhancing the stress responses of probiotics for a lifestyle from gut to product and back again

Before a probiotic bacterium can even begin to fulfill its biological role, it must survive a battery of environmental stresses imposed during food processing and passage through the gastrointestinal tract (GIT). Food processing stresses include extremes in temperature, as well as osmotic, oxidative and food matrix stresses. Passage through the GIT is a hazardous journey for any bacteria with deleterious lows in pH encountered in the stomach to the detergent-like properties of bile in the duodenum. However, bacteria are equipped with an array of defense mechanisms to counteract intracellular damage or to enhance the robustness of the cell to withstand lethal external environments. Understanding these mechanisms in probiotic bacteria and indeed other bacterial groups has resulted in the development of a molecular toolbox to augment the technological and gastrointestinal performance of probiotics. This has been greatly aided by studies which examine the global cellular responses to stress highlighting distinct regulatory networks and which also identify novel mechanisms used by cells to cope with hazardous environments. This review highlights the latest studies which have exploited the bacterial stress response with a view to producing next-generation probiotic cultures and highlights the significance of studies which view the global bacterial stress response from an integrative systems biology perspective.

Identification and characterization of potential autochthonous starter cultures from a Croatian "brand" product "Slavonski kulen"

The microbial population of a traditional Croatian fermented sausage "Slavonski kulen" was isolated, identified and subjected to technological and functional characterization in order to select potential autochthonous functional starter cultures. Dominant microflora were lactic acid bacteria (LAB), followed by staphylococci. Identification of isolated lactobacilli showed domination of Leuconostoc mesenteroides and Lactobacillus acidophilus while Staphylococcus xylosus and Staphylococcus warneri outnumbered the staphylococcal microbiota. Most of the isolated LAB and Staphylococcus species displayed good growth in the presence of 5% of NaCl and at 12, 18 and 22°C. All LAB and most of the staphylococci possess proteolytic activity and only Staphylococcus xylosus had lipolytic activity. All lactobacilli and staphylococci isolates produced significant concentrations of lactic acid (as determined by HPLC) and showed antimicrobial activity against pathogenic test microorganisms. Dominant LAB and Staphylococcus species displayed growth in the presence of 1% bile. Most of the staphylococci and all of lactobacilli showed sensitivity to all antibiotics tested.

Molecular and biochemical properties of the S-layer protein from the wine bacterium Lactobacillus hilgardii B706

Different strains of the genus Lactobacillus can be regularly isolated from must and wine samples. By various physiological activities, they can improve or reduce the wine quality. Lactobacillus hilgardii that is known to survive under harsh wine conditions is classified as a spoilage bacterium, e.g. due to the production of histamine. Many lactobacilli form an S-layer as the outermost cell wall component which has been found to facilitate the colonization of special ecological niches. A detailed understanding of the properties related to their S-layer proteins is necessary to improve the knowledge of the interactions between different bacterial cells and with the surrounding environments. The S-layer protein from the wine-related L. hilgardii strain B706 has been isolated and its gene sequence determined. The deduced amino acid sequence corresponds to a 41 kDa protein with an isoelectric point of 9.6 without additional posttranslational modifications after splitting off the leader peptide. The complete protein is organized in a 32 amino acids signal sequence for membrane translocation, a positively charged N-terminal domain that binds to the cell wall and a negatively charged C-terminal domain. When the S-layer was removed, the corresponding L. hilgardii B706 cells became more sensitive to bacteriolytic enzymes and some wine-related stress conditions. From a practical point of view, the S-layer may be considered as a target for the inhibition of food-spoiling lactobacilli.

Inhibition of Shigella sonnei adherence to HT-29 cells by lactobacilli from Chinese fermented food and preliminary characterization of S-layer protein involvement

In this study, seven lactobacilli with a high degree of antagonistic activity against three pathogens and good adherence to HT-29 cells were selected. The ability of these seven lactobacilli to inhibit adhesion of Shigella sonnei to intestinal mucosa was studied on cultured HT-29 cells. Lactobacilli were added simultaneously with, before or after S. sonnei to test for their effectiveness in exclusion, competition and displacement assays, respectively. Lactobacillus paracasei subp. paracasei M5-L, Lactobacillus rhamnosus J10-L and Lactobacillus casei Q8-L all exhibited significant inhibitory activity. In order to elucidate the inhibitory functions of S-layer proteins, the S-layer proteins were removed with 5 M LiCl from the M5-L, J10-L and Q8-L strains. Under such conditions, inhibition activity was decreased in all three strains, as revealed in exclusion, competition and displacement assays. SDS-PAGE analysis confirmed the presence of S-layer proteins with dominant bands of approximately 45 kDa. Further analysis of S-layer proteins revealed that the hydrophobic amino acids accounted for 40.5%, 41.5% and 43.8% of the total amino acid for the M5-L, J10-L and Q8-L strains, respectively. These findings suggest that the M5-L, J10-L and Q8-L strains possess the ability to inhibit S. sonnei adherence to HT-29 cells, and S-layer proteins are involved in this adhesion inhibition.

Functional roles of aggregation-promoting-like factor in stress tolerance and adherence of Lactobacillus acidophilus NCFM

Aggregation-promoting factors (Apf) are secreted proteins that have been associated with a diverse number of functional roles in lactobacilli, including self-aggregation, the bridging of conjugal pairs, coaggregation with other commensal or pathogenic bacteria, and maintenance of cell shape. In silico genome analysis of Lactobacillus acidophilus NCFM identified LBA0493 as a 696-bp apf gene that encodes a putative 21-kDa Apf protein. Transcriptional studies of NCFM during growth in milk showed apf to be one of the most highly upregulated genes in the genome. In the present study, reverse transcriptase-quantitative PCR (RT-QPCR) analysis revealed that the apf gene was highly induced during the stationary phase compared to that during the logarithmic phase. To investigate the functional role of Apf in NCFM, an Delta apf deletion mutant was constructed. The resulting Delta apf mutant, NCK2033, did not show a significant difference in cell morphology or growth compared to that of the NCFMDelta upp reference strain, NCK1909. The autoaggregation phenotype of NCK2033 in planktonic culture was unaffected. Additional phenotypic assays revealed that NCK2033 was more susceptible to treatments with oxgall bile and sodium dodecyl sulfate (SDS). Survival rates of NCK2033 decreased when stationary-phase cells were exposed to simulated small-intestinal and gastric juices. Furthermore, NCK2033 in the stationary phase showed a reduction of in vitro adherence to Caco-2 intestinal epithelial cells, mucin glycoproteins, and fibronectin. The data suggest that the Apf-like proteins may contribute to the survival of L. acidophilus during transit through the digestive tract and, potentially, participate in the interactions with the host intestinal mucosa.

Evaluation of adhesion capacity, cell surface traits and immunomodulatory activity of presumptive probiotic Lactobacillus strains

Twelve lactobacilli previously isolated from newborn infants' gastrointestinal tract and Feta cheese were further characterized by pulse field gel eletrophoresis (PFGE). All strains exhibited distinct PFGE genotypic patterns with the exception of DC421 and DC423 strains possessing identical patterns. The strains DC421, 2035 and 2012 were found to posses certain cell surface traits such as hydrophobicity, autoaggregation and/or high adhesive capacity suggesting potential immunomodulatory activity. However, application of the dorsal mouse air pouch system revealed that only the DC421, DC429 and 2035 strains exhibited strong immunostimulatory activity such as increased chemotaxis of polymorphonuclear (PMN) cells in association with increased phagocytosis and cytokine production. The same strains also induced immunomodulatory activity in the gut associated lymphoid tissue in mice in the absence of any inflammatory response. All strains induced IgA production while reduced TNFalpha production by small intestine cells. The strains DC421 and DC429 exerted their effect on the intestine through Toll-like receptor TLR2/TLR4/TLR9 mediated signalling events leading to secretion of a certain profile of cytokines in which gamma interferon (IFN-gamma), interleukin (IL)-5, IL-6 and IL-10 are included. The strain 2035 induced similar cytokine profile through the synergy of TLR2/TLR4. This study further supports the eligibility of the air pouch model to discriminate presumptive probiotic Lactobacillus strains exhibiting immunostimulatory activity in the gut. Furthermore, evidence is provided that the cell surface traits examined may not be the only criteria but an alternative and important component of a complex mechanism that enables a microorganism to interact with the host gut to exert its immunoregulatory activity.

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.

Comparison of conventional and molecular methods for the routine confirmation of Listeria monocytogenes in milk products produced domestically in Croatia

Conventional methods for the identification of Listeria in foodstuffs are generally cumbersome and time consuming. The use of primary enrichment in half strength Fraser broth and the use of PALCAM agar were assessed in comparison with API Listeria and polymerase chain reaction (PCR) for their ability to accurately detect and confirm the presence of List. monocytogenes in milk products. The aim of our work was to detect List. monocytogenes in domestic unpasteurised milk, fresh cheese and cream of raw milk taken from four different district of Zagreb-Croatia using conventional (microbiological and biochemical – API test) and PCR methods. Of the 180 milk products samples tested, 27·6% were presumptively positive for Listeria on PALCAM agar. Only 21·3% of samples were confirmed to be positive for Listeria by API Listeria test, and 17·3% were confirmed to be positive for List. monocytogenes by PCR amplification of the hly gene (64 bp). PCR was able to eliminate the false positive and detect all List. monocytogenes in the milk products, unlike the conventional methods used in the industry. These results indicate a low presence of this pathogen in this area (Zagreb) of Croatia. PCR proves to be a sensitive and rapid technique to be included in the procedure of detection of List. monocytogenes in food products and this method is considerably faster than current standard methods.

Probiotic potential of Staphylococcus hominis MBBL 2-9 as anti-Staphylococcus aureus agent isolated from the vaginal microbiota of a healthy woman

AIMS

To isolate and characterize an antagonist for use as probiotic agent in the biocontrol of Staphylococcus aureus.

METHODS AND RESULTS

Bacteria that exhibited antimicrobial activity against Gram-positive bacteria including Staph. aureus were isolated from 12 healthy women, with Staphylococcus hominis MBBL 2-9 showing the strongest activity. The bacteriocin produced by Staph. hominis MBBL 2-9 was purified by 60% ammonium sulfate saturation, ultrafiltration, HLB cartridge and reverse-phase HPLC. The molecular weight was estimated as 2038.2 Da by MALDI-TOF mass spectrometry. The antagonist survived up to 2 h in artificial gastric juice (pH 2.5) and grew in the presence of 1% porcine bile extract. In addition, Staph. hominis MBBL 2-9 adhered effectively to HT-29 epithelial cell line.

CONCLUSION

Staphylococcus hominis MBBL 2-9 exhibited desirable probiotic traits such as acid tolerance, bile resistance and adherence to epithelial cell line. The bacterium also produced a bacteriocin with unique molecular weight and high antimicrobial activity similar to traditional antibiotics.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study is the first report of a bacteriocin-producing Staph. hominis MBBL 2-9 that has potential for use as a probiotic agent against Staph. aureus.