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

Evaluation in Mice of a Conjugate Vaccine for Cholera Made from Vibrio cholerae O1 (Ogawa) O-Specific Polysaccharide

Background: Protective immunity against cholera is serogroup specific. Serogroup specificity in Vibrio cholerae is determined by the O-specific polysaccharide (OSP) of lipopolysaccharide (LPS). Generally, polysaccharides are poorly immunogenic, especially in young children. Methodology Here we report the evaluation in mice of a conjugate vaccine for cholera (OSP:TThc) made from V. cholerae O1 Ogawa O-Specific Polysaccharide–core (OSP) and recombinant tetanus toxoid heavy chain fragment (TThc). We immunized mice intramuscularly on days 0, 21, and 42 with OSP:TThc or OSP only, with or without dmLT, a non-toxigenic immunoadjuvant derived from heat labile toxin of Escherichia coli. Principal Findings We detected significant serum IgG antibody responses targeting OSP following a single immunization in mice receiving OSP:TThc with or without adjuvant. Anti-LPS IgG responses were detected following a second immunization in these cohorts. No anti-OSP or anti-LPS IgG responses were detected at any time in animals receiving un-conjugated OSP with or without immunoadjuvant, and in animals receiving immunoadjuvant alone. Responses were highest following immunization with adjuvant. Serum anti-OSP IgM responses were detected in mice receiving OSP:TThc with or without immunoadjuvant, and in mice receiving unconjugated OSP. Serum anti-LPS IgM and vibriocidal responses were detected in all vaccine cohorts except in mice receiving immunoadjuvant alone. No significant IgA anti-OSP or anti-LPS responses developed in any group. Administration of OSP:TThc and adjuvant also induced memory B cell responses targeting OSP and resulted in 95% protective efficacy in a mouse lethality cholera challenge model. Conclusion: We describe a protectively immunogenic cholera conjugate in mice. Development of a cholera conjugate vaccine could assist in inducing long-term protective immunity, especially in young children who respond poorly to polysaccharide antigens

Individuals with Le(a+b−) Blood Group Have Increased Susceptibility to Symptomatic Vibrio cholerae O1 Infection

Cholera remains a severe diarrheal disease, capable of causing extensive outbreaks and high mortality. Blood group is one of the genetic factors determining predisposition to disease, including infectious diseases. Expression of different Lewis or ABO blood group types has been shown to be associated with risk of different enteric infections. For example, individuals of blood group O have a higher risk of severe illness due to V. cholerae compared to those with non-blood group O antigens. In this study, we have determined the relationship of the Lewis blood group antigen phenotypes with the risk of symptomatic cholera as well as the severity of disease and immune responses following infection. We show that individuals expressing the Le(a+b−) phenotype were more susceptible to symptomatic cholera, while Le(a–b+) expressing individuals were less susceptible. Individuals with the Le(a–b−) blood group had a longer duration of diarrhea when infected, required more intravenous fluid replacement, and had lower plasma IgA antibody responses to V. cholerae LPS on day 7 following infection. We conclude that there is an association between the Lewis blood group and the risk of cholera, and that this risk may affect the outcome of infection as well as possibly the efficacy of vaccination

SND1 promotes Th1/17 immunity against chlamydial lung infection through enhancing dendritic cell function.

To date, no reports have linked the multifunctional protein, staphylococcal nuclease domain-containing protein 1 (SND1), to host defense against intracellular infections. In this study, we investigated the role and mechanisms of SND1, by using SND1 knockout (SND1-/-) mice, in host defense against the lung infection of Chlamydia muridarum, an obligate intracellular bacterium. Our data showed that SND1-/- mice exhibited significantly greater body weight loss, higher organism growth, and more severe pathological changes compared with wild-type mice following the infection. Further analysis showed significantly reduced Chlamydia-specific Th1/17 immune responses in SND1-/- mice after infection. Interestingly, the dendritic cells (DCs) isolated from SND1-/- mice showed lower costimulatory molecules expression and IL-12 production, but higher IL-10 production compared with those from wild-type control mice. In the DC-T cell co-culture system, DCs isolated from SND1-/- infected mice showed significantly reduced ability to promote Chlamydia-specific IFN-γ producing Th1 cells but enhanced capacity to induce CD4+T cells into Foxp3+ Treg cells. Adoptive transfer of DCs isolated from SND1-/- mice, unlike those from wild-type control mice, failed to protect the recipients against challenge infection. These findings provide in vivo evidence that SND1 plays an important role in host defense against intracellular bacterial infection, and suggest that SND1 can promote Th1/17 immunity and inhibit the expansion of Treg cells through modulation of the function of DCs

Type 1 pili are required for virulence in the rabbit ileal loop assay.

<p>Type 1 pili are required for optimal bacterial engagement of rabbit intestinal epithelia. <b>a.</b> sections of rabbit ileum in which attached bacteria (green) are identified with anti-O78 (top panel) or anti-FimH (bottom panel). Nuclei are stained with DAPI (blue) and membranes are stained with CellMask (red). <b>b.</b> bacteria adherent to the ileal mucosal surface following infection with wild type ETEC H10407 or <i>fimH</i> and <i>fimA</i> mutants. <b>c.</b> Type 1 pili are required for toxicity in the rabbit ileal loop assay. Shown in the graph is the amount of fluid accumulation in each loop infected with WT or <i>fimH</i> or <i>fimA</i> mutants 18 h post inoculation. Loops infected with <i>eltAB</i> mutants or mock infected (PBS) were used as controls. Data represent the summary of experiments from 7 different rabbits (n = 7). Inset image shows infected ileal loops from one representative experiment. Each loop in the inset image is labeled with the infecting bacterial strain or with the negative control (PBS).</p

Enhanced presentation of mannosylated glycoproteins increases FimH binding and ETEC adhesion.

<p><b>a.</b> Confocal microscopy images detecting FimHLD binding to the kifunensine treated CIE. Biotinylated FimHLD was detected with streptavidin-conjugated fluorescent nanocrystals (Qdot, green) and nuclei with DAPI (blue). <b>b.</b> Quantitative analysis of FimHLD binding to CIE represented in panels <b>a</b> using Volocity three-dimensional (3D) image analysis software (version 6.2; PerkinElmer, Inc.). Data represent mean ± standard deviation of results of 3 independent experiments each with triplicate wells per concentration tested (n = 9). <b>c.</b> Confocal microscopic images showing ETEC adhesion to kifunensine treated CIE. The CIE grown on trans-well filters were treated with kifunensine and infected with WT ETEC or <i>fimH</i> mutants. One hour post infection wells were processed for microscopic examination. Bacteria (green), cell membrane (red), DAPI (blue). <b>d.</b> Quantitative analysis was done by counting number of bacteria present per focus area. Horizontal dashed lines represent geometric mean of 25 total data points combined from 2 replicate experiments. P values were calculated by nonparametric Mann-Whitney test. *** indicates p<0.0001.</p

Type 1 pili expression promotes optimal adhesion of ETEC to intestinal epithelia.

<p><b>a.</b> Transmission electron micrograph of ETEC H10407 expressing type 1 pili. The FimH tip adhesin was detected using α-FimH antibody and gold secondary antibody conjugate. <b>b</b>. Flow cytometric analysis of type 1 pili expression by ETEC H10407 and <i>fimH</i> mutants. <b>c.</b> Assessment of type 1 pili function using yeast agglutination assays. Negative yeast agglutination reflected the loss of type 1 pili activity. <b>d.</b> FimA immunoblot of type 1 pili extracts from static culture of WT ETEC, <i>fimH</i> mutants and mutants complemented with wild type <i>fimH</i> gene (p<i>fimH</i>). The <i>fimH</i> mutant complemented with a plasmid encoding a Q133K substitution in FimH is included as a negative control. <b>e.</b> Confocal microscopic images showing adhesion of WT ETEC, <i>fimH</i> mutants or complemented mutants to polarized cultured intestinal epithelia. Bacteria (anti-O78, green), cell membrane (CellMask, red), nuclei (DAPI, blue). <b>f.</b> Quantitative analysis was done by counting number of bacteria per focus area. Horizontal dashed lines represent geometric means of 3 combined individual experiments. P values were calculated by nonparametric Mann-Whitney test. *** indicates p<0.0001.</p

FimH adhesin of ETEC interacts with intestinal epithelial cells.

<p><b>a.</b> Confocal microscopy images show binding of the biotinylated FimH lectin domain (FimHLD) or FimHLD:Q133K to the apical surface cultured intestinal epithelium (CIE). Biotinylated FimHLD was detected with streptavidin-conjugated fluorescent nanocrystals (Qdot, green); plasma membranes were stained with CellMask (red) and nuclei with DAPI (blue). Image at right shows three dimensional reconstruction of z stacks of CIE following interaction with FimHLD or the mutant protein. <b>b.</b> Quantitative analysis of FimHLD binding to CIE represented in panels <b>a</b> using Volocity three-dimensional (3D) image analysis software (version 6.2; PerkinElmer, Inc.). P value was calculated using nonparametric Mann-Whitney testing. <b>c.</b> Immunoelectron microscopy images of CIE infected with ETEC H10407. Left panel, microvilli structure at the apical surface of the CIE; right panels show immunogold labeling of FimH localized to the ETEC-host interacting surface.</p

Type 1 pili mediated interactions enhance toxin delivery.

<p><b>a.</b> Quantification of intracellular cGMP in infected cells. Cells were infected with WT ETEC in the absence or presence mannose sugar or with <i>fimH</i> or <i>fimA</i> mutants. Cells infected with <i>estH/estP</i> mutants which lack production of both heat stable toxins ST-H (ST-1b) and ST-P (ST-1a), represent basal level of cGMP in cells. <b>b.</b> Quantification of the amount of intracellular cAMP in infected cells. Cells were infected with WT ETEC in the absence or presence mannose sugar or with <i>fimH</i> or <i>fimA</i> mutants. Cells infected with <i>eltAB</i>, LT mutants, represent basal level of cAMP in cells. <b>c.</b> LT secretion by different mutants. Each bar represent mean with SEM (error bar) of 2 experiments consisting of 5 replicates per experiment for each strain. All P values were calculated by nonparametric Mann-Whitney test. *** p<0.0001.</p

Type 1 pili are required for optimal adhesion to small intestinal epithelia.

<p><b>a.</b> Representative laser scanning confocal microscopy (LSCM) images of sections prepared from human small intestinal enteroid-derived polarized monolayers infected with WT H10407 (red, anti-O78). Surface staining with the UEA1 lectin is shown in green. Nuclei are stained in blue (DAPI). <b>b.</b> Three dimensional reconstruction of LSCM z stacks of ETEC H10407 infected polarized monolayers showing the distribution of zonula occludens-1 (ZO-1, green) at the apical surface. Bacteria were visualized with anti-O78 (red) and nuclei are stained with DAPI (blue). <b>c.</b> Transmission electron microscopy images of ETEC H10407 adhering to microvilli on the surface of small intestinal monolayers (magnification 7500x and 15000x for left and right images respectively). <b>d.</b> LCSM images of wild type (wt) versus <i>fimH</i> mutant bacteria adherent to the surface of small intestinal enteroids Bacteria were visualized with anti-O78 (green) and cell membranes with CellMask (red), nuclei (DAPI, blue). <b>e.</b> Quantitative analysis of ETEC adhesion to enteroid-derived monolayers represented in panel <b>d</b>. Each dot plot represents adhesion data obtained using ileal cell derived from two individual subjects. Horizontal lines represent geometric means of data combined from 2 independent experiments. P values were calculated by nonparametric Mann-Whitney testing.</p