Host Enterocytes Research Articles

Stabilization of F-actin by Salmonella effector SipA resembles the structural effects of inorganic phosphate and phalloidin

Entry of Salmonella into host enterocytes relies on its pathogenicity island 1 effector SipA. We found that SipA binds to F-actin in a 1:2 stoichiometry with sub-nanomolar affinity. A cryo-EM reconstruction revealed that SipA's globular core binds at the groove between actin strands, whereas the extended C-terminal arm penetrates deeply into the inter-strand space, stabilizing F-actin from within. The unusually strong binding of SipA is achieved by a combination of fast association via the core and very slow dissociation dictated by the arm. Similar to Pi, BeF3, and phalloidin, SipA potently inhibited actin depolymerization by actin depolymerizing factor (ADF)/cofilin, which correlated with increased filament stiffness, supporting the hypothesis that F-actin's mechanical properties contribute to the recognition of its nucleotide state by protein partners. The remarkably strong binding to F-actin maximizes the toxin's effects at the injection site while minimizing global influence on the cytoskeleton and preventing pathogen detection by the host cell.

Molecular characterisation of Entamoeba histolytica UDP-glucose 4-epimerase, an enzyme able to provide building blocks for cyst wall formation.

In the human host, the protozoan parasite Entamoeba histolytica is adapted to a non-invasive lifestyle in the colon as well as to an invasive lifestyle in the mesenterial blood vessels and the liver. This means to cope with bacteria and human cells as well as various metabolic challenges. Galactose and N-acetylgalactosamine (GalNAc) are sugars of great importance for the amoebae, they attach to the host mucus and enterocytes via their well-studied Gal/GalNAc specific lectin, they carry galactose residues in their surface glycans, and they cleave GalNAc from host mucins. The enzyme UDP-glucose 4-epimerase (GalE) works as a bridge between the galactose and glucose worlds, it can help to generate glucose for glycolysis from phagocytosis products containing galactose as well as providing UDP-galactose necessary for the biosynthesis of galactose-containing surface components. E. histolytica contains a single galE gene. We recombinantly expressed the enzyme in Escherichia coli and used a spectrophotometric assay to determine its temperature and pH dependency (37°C, pH 8.5), its kinetics for UDP-glucose (Km = 31.82 μM, Vmax = 4.31 U/mg) and substrate spectrum. As observed via RP-HPLC, the enzyme acts on UDP-Glc/Gal as well as UDP-GlcNAc/GalNAc. Previously, Trypanosoma brucei GalE and the bloodstream form of the parasite were shown to be susceptible to the three compounds ebselen, a selenoorganic drug with antioxidant properties, diethylstilbestrol, a mimic of oestrogen with anti-inflammatory properties, and ethacrynic acid, a loop diuretic used to treat oedema. In this study, the three compounds had cytotoxic activity against E. histolytica, but only ebselen inhibited the recombinant GalE with an IC50 of 1.79 μM (UDP-Gal) and 1.2 μM (UDP-GalNAc), suggesting that the two other compounds are active against other targets in the parasite. The importance of the ability of GalE to interconvert UDP-GalNAc and UDP-GlcNAc may be that the trophozoites can generate precursors for their own cyst wall from the sugar subunits cleaved from host mucins. This finding advances our understanding of the biochemical interactions of E. histolytica in its colonic environment.

Opportunistic yeast pathogenCandidaspp.: Secreted and membrane-bound virulence factors

Candida virulence factors (VFs) including mainly enzymes and proteins play vital roles in breaching the human intestinal barrier and causing deadly invasive candidiasis. Limited VFs' structural studies hinder deeper comprehension of their mechanisms and thus the design of vaccines and antifungal drugs against fungal infections.

Enterocytozoon bieneusi

Enterocytozoon bieneusi is a microsporidium, related to Cryptomycota and fungi, which has been reported globally in a wide range of mammalian and avian hosts. It is responsible for over 90% of documented cases of human microsporidiosis and causes varying clinical symptoms, typically diarrhea and wasting. Infection begins with ingestion of spores in contaminated water and food. Spores deliver the infective sporoplasm into host enterocytes via the discharged polar tube. Meronts form and develop into multinucleated plasmodia, which undergo sporogony to form sporoblasts and then mature spores. Spores released from infected cells are shed with the stool. Sequence analysis of the ribosomal internal transcribed spacer (ITS) has identified over 500 genotypes, some of which are generalists of zoonotic importance and pose a threat to public health. Population genetic data uphold the zoonotic nature and host specificity of the parasite. Knowledge of its pathogenicity, immune responses, and expanded treatment options are urgently needed.

Gut bugs and systemic disease risk

Microbiota What people eat has an immediate selective effect on the microbial populations resident in the gut. A high-fat diet is associated with the occurrence of microbes that catabolize choline and the accumulation of trimethylamine N -oxide (TMAO) in the bloodstream, a contributing factor for heart disease. Yoo et al. explored the microbial organisms and pathways that convert choline into TMAO in mice. Although gene clusters for choline metabolism are found widely among the microbiota, it is only the facultative anaerobes that become abundant in hosts on a high-fat diet. A high-fat diet impairs mitochondrial uptake of oxygen into host enterocytes and elevates nitrate in the mucus, which in turn weakens healthy anaerobic gut function. Facultative anaerobes such as the pathobiont Escherichia coli become dominant, which leads to an overall increase in the amount of choline catabolized into the precursor for TMAO. Whether this pathway plays a role in heart disease remains unclear. Science , aba3683, this issue p. [813][1] [1]: /lookup/doi/10.1126/science.aba3683

High-fat diet-induced colonocyte dysfunction escalates microbiota-derived trimethylamine N-oxide.

A Western-style, high-fat diet promotes cardiovascular disease, in part because it is rich in choline, which is converted to trimethylamine (TMA) by the gut microbiota. However, whether diet-induced changes in intestinal physiology can alter the metabolic capacity of the microbiota remains unknown. Using a mouse model of diet-induced obesity, we show that chronic exposure to a high-fat diet escalates Escherichia coli choline catabolism by altering intestinal epithelial physiology. A high-fat diet impaired the bioenergetics of mitochondria in the colonic epithelium to increase the luminal bioavailability of oxygen and nitrate, thereby intensifying respiration-dependent choline catabolism of E. coli In turn, E. coli choline catabolism increased levels of circulating trimethlamine N-oxide, which is a potentially harmful metabolite generated by gut microbiota.

Functional and Genomic Variation between Human-Derived Isolates of Lachnospiraceae Reveals Inter- and Intra-Species Diversity

Bacteria belonging to the Lachnospiraceae family are abundant, obligate anaerobic members of the microbiota in healthy humans. Lachnospiraceae impact their hosts by producing short-chain fatty acids, converting primary to secondary bile acids, and facilitating colonization resistance against intestinal pathogens. To increase our understanding of genomic and functional diversity between members of this family, we cultured 273 Lachnospiraceae isolates representing 11 genera and 27 species from human donors and performed whole-genome sequencing assembly and annotation. This analysis revealed substantial inter- and intra-species diversity in pathways that likely influence an isolate's ability to impact host health. These differences are likely to impact colonization resistance through lantibiotic expression or intestinal acidification, influence host mucosal immune cells and enterocytes via butyrate production, or contribute to synergism within a consortium by heterogenous polysaccharide metabolism. Identification of these specific functions could facilitate development of probiotic bacterial consortia that drive and/or restore invivo microbiome functions.

The consequences of altered microbiota in immune-related chronic kidney disease.

The normal gut microbiome modulates host enterocyte metabolism and shapes local and systemic immunity. Accumulation of urea and other waste products in chronic kidney disease induces gut dysbiosis and intestinal wall inflammation (leaky gut). There are decreased numbers of bacteria that generate short-chain fatty acids, which are an important nutrient source for host enterocytes and also contribute to regulation of the host immune system. Anaerobic proteolytic bacteria that express urease, uricase and indole and p-cresol enzymes, such as Enterobacteria and Enterococci, are increased. Microbial-derived uremic toxins such as indoxyl sulfate and trimethylamine N-oxide contribute to the pathophysiology of immune-related kidney diseases such as diabetic nephropathy, lupus nephritis and immunoglobulin A (IgA) nephropathy. Animal and clinical studies suggest potential benefits of dietary and probiotic interventions in slowing the progression of immune-related kidney diseases.

Obesity, Motility, Diet, and Intestinal Microbiota-Connecting the Dots.

The goal of the present review is to explore the relationship between dietary changes and alterations in gut microbiota that contribute to disorders of gut motility and obesity. We review the microbiota changes that are seen in obesity, diarrhea, and constipation and look at potential mechanisms of how dysbiosis can predispose to these. We find that microbial metabolites, particularly short chain fatty acids, can lead to signaling changes in the host enterocytes. Microbial alteration leading to both motility disorders and obesity may be mediated by the release of hormones including glucagon-like peptides 1 and 2 (GLP-1, GLP-2) and polypeptide YY (PYY). These pathways provide avenues for microbiota-targeted interventions that can treat both disorders of motility and obesity. In summary, multiple mechanisms contribute to the interplay between the microbial dysbiosis, obesity, and dysmotility.

To B12 or not to B12: Five questions on the role of cobalamin in host-microbial interactions.

Vitamins are organic compounds that are essential to the health of an organism. Humans cannot synthesize vitamins but obtain vitamins through dietary intake. Cobalamin, or vitamin B12, refers to a group of corrinoid molecules that contains a corrin ring with a central cobalt molecule [1]. Cobalamin is a cofactor for the highly conserved enzymes methionine synthase (MetH) and methylmalonyl-CoA mutase (MCM), which function in amino acid synthesis and fatty- and amino acid breakdown, respectively, in both bacteria and mammals [1]; therefore, cobalamin plays a key role in homeostatic functions. Indeed, in humans, cobalamin deficiency can lead to decreased activity of MetH and MCM and result in megaloblastic anemia in addition to severe neurological symptoms. Besides its role as a cofactor for MetH and MCM, cobalamin is also used by many bacteria as a cofactor for additional processes, including metabolism and gene regulation. Cobalamin impacts host–microbe interactions by altering host and bacterial physiology at intestinal and extraintestinal sites. We discuss the current understanding of cobalamin in host–microbiota–pathogen interactions, highlighting recent investigations that deepen our appreciation of this molecule. How do mammals acquire cobalamin? Only a limited number of bacteria and archaea generate cobalamin de novo [1]. Moreover, plants and fungi do not require cobalamin; therefore, humans obtain cobalamin through consumption of animal products. During digestion, cobalamin is absorbed in the ileum. Although some colonic bacteria produce cobalamin, humans are not able to uptake cobalamin produced at this location, and thus, the small intestine is the sole site of absorption. The mammalian protein intrinsic factor (IF) is essential to bind and absorb cobalamin. IF is produced in the stomach and binds cobalamin in the small intestine, in which IF-bound cobalamin is subsequently absorbed into circulation [2] (Fig 1). Open in a separate window Fig 1 Cobalamin in the healthy human intestinal tract. Ingested food containing cobalamin enters the stomach. IF is produced in the stomach and binds cobalamin in the small intestine. There, cobalamin–IF complexes are absorbed by host enterocytes in the terminal ileum (indicated by outward arrows in small intestine). In the colon, the microbiota take up unabsorbed cobalamin. Additionally, some members of the microbiota produce cobalamin, which can also be taken up by other microbiota members. Cobalamin that remains unabsorbed by the host and not taken up by the microbiota is excreted in stool (outward arrow in colon). IF, intrinsic factor.

Highly conserved type 1 pili promote enterotoxigenic E. coli pathogen-host interactions.

Enterotoxigenic Escherichia coli (ETEC), defined by their elaboration of heat-labile (LT) and/or heat-stable (ST) enterotoxins, are a common cause of diarrheal illness in developing countries. Efficient delivery of these toxins requires ETEC to engage target host enterocytes. This engagement is accomplished using a variety of pathovar-specific and conserved E. coli adhesin molecules as well as plasmid encoded colonization factors. Some of these adhesins undergo significant transcriptional modulation as ETEC encounter intestinal epithelia, perhaps suggesting that they cooperatively facilitate interaction with the host. Among genes significantly upregulated on cell contact are those encoding type 1 pili. We therefore investigated the role played by these pili in facilitating ETEC adhesion, and toxin delivery to model intestinal epithelia. We demonstrate that type 1 pili, encoded in the E. coli core genome, play an essential role in ETEC virulence, acting in concert with plasmid-encoded pathovar specific colonization factor (CF) fimbriae to promote optimal bacterial adhesion to cultured intestinal epithelium (CIE) and to epithelial monolayers differentiated from human small intestinal stem cells. Type 1 pili are tipped with the FimH adhesin which recognizes mannose with stereochemical specificity. Thus, enhanced production of highly mannosylated proteins on intestinal epithelia promoted FimH-mediated ETEC adhesion, while conversely, interruption of FimH lectin-epithelial interactions with soluble mannose, anti-FimH antibodies or mutagenesis of fimH effectively blocked ETEC adhesion. Moreover, fimH mutants were significantly impaired in delivery of both heat-stable and heat-labile toxins to the target epithelial cells in vitro, and these mutants were substantially less virulent in rabbit ileal loop assays, a classical model of ETEC pathogenesis. Collectively, our data suggest that these highly conserved pili play an essential role in virulence of these diverse pathogens.

The Type III Effector NleD from Enteropathogenic Escherichia coli Differentiates between Host Substrates p38 and JNK.

Enteropathogenic Escherichia coli (EPEC) is a gastrointestinal pathogen that utilizes a type III secretion system (T3SS) to inject an array of virulence effector proteins into host enterocytes to subvert numerous cellular processes for successful colonization and dissemination. The T3SS effector NleD is a 26-kDa zinc metalloprotease that is translocated into host enterocytes, where it directly cleaves and inactivates the mitogen-activated protein kinase signaling proteins JNK and p38. Here a library of 91 random transposon-based, in-frame, linker insertion mutants of NleD were tested for their ability to cleave JNK and p38 during transient transfection of cultured epithelial cells. Immunoblot analysis of p38 and JNK cleavage showed that 7 mutant derivatives of NleD no longer cleaved p38 but maintained the ability to cleave JNK. Site-directed mutation of specific regions surrounding the insertion sites within NleD revealed that a single amino acid, R203, was essential for cleavage of p38 but not JNK in a direct in vitro cleavage assay, in transiently transfected cells, or in EPEC-infected cells. Mass spectrometry analysis narrowed the cleavage region to within residues 187 and 213 of p38. Mutation of residue R203 within NleD to a glutamate residue abolished the cleavage of p38 and impaired the ability of NleD to inhibit AP-1-dependent gene transcription of a luciferase reporter. Furthermore, the R203 mutation abrogated the ability of NleD to dampen interleukin-6 production in EPEC-infected cells. Overall, this work provides greater insight into substrate recognition and specificity by the type III effector NleD.

Self-Conjugation of the Enteropathogenic Escherichia coli Adherence Factor Plasmid of Four Typical EPEC Isolates.

The enteropathogenic Escherichia coli (EPEC) adherence factor plasmid (pEAF) encodes the proteins involved in the biogenesis of the bundle-forming pilus (BFP), a key virulence factor that mediates microcolony formation and the localized adherence phenotype on the surface of the host enterocytes. The presence or absence of this plasmid defines typical EPEC (tEPEC) and atypical EPEC (aEPEC), respectively. Although lateral transfer of pEAF has been evidenced by phylogenetic studies, conjugal transfer ability has been experimentally established only for two pEAF plasmids from strains isolated in the late 60s. In the present work, we tested the self-conjugation ability of four pEAF plasmids from tEPEC strains isolated between 2007 and 2008 from children in Peru and the potential of aEPEC to receive them. A kanamycin resistance cassette was inserted into donor pEAF plasmids in order to provide a selectable marker in the conjugation experiments. Two aEPEC isolated from the same geographic region were used as recipient strains along with the laboratory E. coli DH5α strain. Here we show that the four pEAF plasmids tested are self-conjugative, with transfer frequencies in the range of 10−6 to 10−9. Moreover, the generation of aEPEC strains harboring pEAF plasmids provides valuable specimens to further perform functional studies.

Initial events in the breakthrough of the epithelial barrier of the small intestine by Angiostrongylus cantonensis

Although the third-stage larvae of Angiostrongylus cantonensis (AcL3) are thought to initiate infection by penetrating the epithelium of the small intestine, the mode of intestinal invasion remains obscure. Considering the inaccessibility of the gut tract and the need to sacrifice animals for this type of study, we devised an in vitro cell-parasite co-culture system to examine the initial cellular and molecular events between AcL3 and host epithelia. No apoptosis augmentation was detected in enterocytes after introduction of larvae. A significant increase in dead cells was detected in IEC-6, NCM460 and 293T after incubating for 4 h, with AcL3 wounding rat small intestinal epithelial cells IEC-6 more rapidly. Under a scanning electron microscope (SEM), cell gap opening was visualized in the IEC-6 monolayer treated with AcL3. Loosening of the extracellular matrix (ECM) of the monolayer was found to be involved in the parasite-cell interactions. Pretreating the AcL3 with a protease inhibitor attenuated its penetration ability of the artificial intestine barrier. In conclusion, AcL3 broke through the intestinal barrier of the host with the assistance of mechanical injury and the opening of a cell gap, but without causing apoptosis. The interaction platform presented here may provide direct insight into the cellular and molecular events during worm invasion of host enterocytes.

Receptor for the F4 fimbriae of enterotoxigenic Escherichia coli (ETEC).

Infection with F4(+) enterotoxigenic Escherichia coli (ETEC) responsible for diarrhea in neonatal and post-weaned piglets leads to great economic losses in the swine industry. These pathogenic bacteria express either of three fimbrial variants F4ab, F4ac, and F4ad, which have long been known for their importance in host infection and initiating protective immune responses. The initial step in infection for the bacterium is to adhere to host enterocytes through fimbriae-mediated recognition of receptors on the host cell surface. A number of receptors for ETEC F4 have now been described and characterized, but their functions are still poorly understood. The current review summarizes the latest research addressing the characteristics of F4 fimbriae receptors and the interactions of F4 fimbriae and their receptors on host cells. These include observations that as follows: (1) FaeG mediates the binding activities of F4 and is an essential component of the F4 fimbriae, (2) the F4 fimbrial receptor gene is located in a region of chromosome 13, (3) the biochemical properties of F4 fimbrial receptors that form the binding site of the bacterium are now recognized, and (4) specific receptors confer susceptibility/resistance to ETEC F4 infection in pigs. Characterizing the host-pathogen interaction will be crucial to understand the pathogenicity of the bacteria, provide insights into receptor activation of the innate immune system, and develop therapeutic strategies to prevent this illness.

Analysis of differentially expressed genes of Trichinella spiralis larvae activated by bile and cultured with intestinal epithelial cells using real-time PCR

The activation of Trichinella spiralis muscle larvae (ML) by exposure to intestinal contents or bile and the intestinal epithelial cells (IECs) themselves are two pivotal requirements for the in vitro larval invasion of IECs. However, it is yet unknown which genes are involved in the process of larval invasion. The purpose of the present study was to analyze the differentially expressed genes of T. spiralis larvae activated by bile and cultured with IECs by using real-time polymerase chain reaction. Ten T. spiralis genes encoded the proteins produced by the larvae after co-culture with IECs were selected. Compared with untreated ML, four genes were up-regulated in both bile-activated and cell-cultured larvae, including calcium-dependent secretion activator (Csa; 2.55- and 16.04-fold, respectively), multi cystatin-like domain protein precursor (Mcd; 4.36 and 52), serine protease (Sp; 2.03 and 20.02), and intermediate filament protein ifa-1 (Ifa 1; 2 and 3.31). The expression of two genes, enolase (Eno; 1.51) and ribosomal protein S6 kinase beta-1 (Rsk; 1.49), was up-regulated only in cell-cultured larvae, not in bile-activated larvae. The expression of secreted 5'-nucleotidase (5N; 1.42) and putative serine protease (Psp; 1.41) was up-regulated in bile-activated larvae, but was not changed or down-regulated after cultured with IECs. ATP synthase F1, beta subunit (ATPase; 0.58 and 0.51) and serine protease precursor (Spp; 0.42 and 0.65) were down-regulated in both bile-activated and cell-cultured larvae. This study provide some differentially expressed genes among the untreated (normal), bile-activated and cell-cultured larvae of T. spiralis. The up-regulated genes might be related with the larval invasion of IECs, but their exact biological functions need to be further investigated. This study will be helpful to further elucidate the molecular mechanism of the invasion of IECs by T. spiralis larvae and to better understand the interaction between parasite and host enterocytes.

Construction and use of a Trichinella spiralis phage display library to identify the interactions between parasite and host enterocytes

Although it has been known for many years that Trichinella spiralis initiates infection by penetrating the columnar epithelium of the small intestine, the mechanisms by which T. spiralis infective larvae recognize and invade the intestinal epithelial cells (IECs) are unknown. It is speculated that the molecular interactions between the parasite and host enterocytes may mediate the recognition and invasion of IECs by T. spiralis. However, no Trichinella proteins that interact with the enterocytes have been identified previously. The aim of this study was to identify Trichinella proteins that bind to IECs by screening a T7 phage display cDNA library constructed using messenger RNA from T. spiralis intestinal infective larvae. Following five rounds of biopanning, sequencing, and bioinformatics analysis, ten T. spiralis proteins (Tsp1-Tsp10) with significant binding to normal mouse IECs were identified. The results of the protein classification showed that six proteins (Tsp1, calcium-transporting ATPase 2 protein; Tsp4, ovochymase-1; Tsp6, T-complex protein 1 subunit eta; Tsp7, glycosyl hydrolase family 47; Tsp8, DNA replication licensing factor MCM3; and Tsp10, nudix hydrolase) of these T. spiralis proteins were annotated with putative molecular functions. Out of the six proteins, five have catalytic activity, four have binding activity, and one has transporter activity. Anti-Tsp10 antibodies prevented the in vitro partial invasion of IECs by infective larvae and the mice immunized with the recombinant phage T7-Tsp10 showed a 62.8% reduction in adult worms following challenge with T. spiralis muscle larvae. Although their biological functions are not yet fully known, these proteins might be related to the larval invasion of host enterocytes. Future experiments will be necessary to ascertain whether these proteins play important roles in the recognition and invasion of host enterocytes. The construction and biopanning of Trichinella phage display libraries provide a novel approach for searching for candidate genes that are related to invasion and for identifying protein interactions between parasite and host.

Morphological changes and viability ofCryptosporidium parvumsporozoites after excystation in cell-free culture media

Cryptosporidium parvum, belonging to the phylum Apicomplexa, is a major cause of waterborne gastroenteritis throughout the world. The sporozoites are thought to invade host enterocytes using an active process termed gliding motility. However, the biological and morphological changes within the sporozoites during this process are not fully understood. In the present study, excysted sporozoites of C. parvum were analysed ultrastructurally in vitro and their viability was evaluated using fluorescent dyes. The sporozoites excysted from oocysts changed morphologically from banana-shaped to rod-shaped and finally to a rounded shape, in culture media in 3 h. Transmission microscopy revealed that the distance between the apical end and the nucleus was markedly reduced, dense granules were present close to the rhoptry in the apical region, amylopectin granules were absent, and membranes of round sporozoites were less clear. A fluorescent assay showed that the rate of survival decreased from 89% to 56% at 0-3 h (84.3% for banana-shaped and 49.2% for rod-shaped sporozoites). Therefore, post-excysted sporozoites in vitro underwent morphological changes and a rapid loss of viability. This staining method is useful, inexpensive and provides an alternative to more costly and intensive flow cytometric assays or infectivity assays with host cells in vitro.

Addressing the effects of Salmonella internalization in host cell signaling on a reverse‐phase protein array

Through acute enteric infection, Salmonella invades host enterocytes and reproduces intracellularly into specialized vacuolae. This involves changes in host cell signaling elicited by bacterial proteins delivered via type III secretion systems (TTSS). One of the two TTSSs of Salmonella enterica serovar Typhimurium encoded by the Salmonella pathogenicity island-1, triggers bacterial internalization. Among the effector proteins translocated by this TTSS, the GTPase modulator SopE/E2 and the phosphoinositide phosphatase SigD are known to play key roles in these processes. To better understand their contribution to re-programming host cell pathways, we used ZeptoMARK reverse-phase protein array technology, which allows printing 32-sample lysate arrays that can be analyzed with phospho-specific antibodies to evaluate the phosphorylation of signaling proteins. Lysates were obtained at different times after infection of HeLa cells with WT, TTSS-deficient, sopE/E2 and sigD single and double deletants, as well as different sigD Salmonella mutants. Our analysis detected activation of p38, JNK and ERK mitogen-activated protein kinases, mainly dependent on SopE/E2, as well as SigD-dependent phosphorylation of PKB/Akt and its targets GSK-3beta and FKHR/FoxO. This is the first time that reverse-phase protein array technology is used in the cellular microbiology field, demonstrating its value to screen for host signaling events through bacterial infection.

Mechanisms involved in the intestinal interaction between host and bifidobacteria

Bifidobacteria constitute up to 3% of the total human intestinal microbiota and represent one of the most important healthpromoting bacterial groups of the gut microbial ecosystem. Recently, the interaction between Bifidobacterium and the human plasminogen system has been reported, raising the question of the role of this system in the bifidobacterial ecology in the human gastrointestinal tract. Here we investigate the effect of plasminogen on the adhesion of Bifidobacterium lactis BI07 to enterocyte-like Caco-2 cells. According to our experimental data, in the presence of human plasminogen the adhesion of B. lactis BI07 to Caco-2 cells significantly increases. Therefore, we can hypothesize a plasminogen-mediated early adhesion step of B. lactis BI07 to Caco-2 cells. Our findings open the way for further investigations to thoroughly assess the role of plasminogen in the interaction between bifidobacteria and host enterocytes. Key words: Bifidobacteria, plasminogen, enterocytes, gastrointestinal tract, microbiota, adhesion