Morphological diversity among members of the gastrointestinal microflora

Segmented filamentous bacteria in a defined bacterial cocktail induce intestinal inflammation in SCID mice reconstituted with CD45RBhigh CD4+ T cells

BACKGROUND

The aim was to analyze the influence of intestinal microbiota on the development of intestinal inflammation. We used the model of chronic inflammation that develops spontaneously in the colon of conventional severe combined immunodeficiency (SCID) mice restored with the CD45 RB(high) subset of CD4+T cells isolated from the spleen of normal BALB/c mice.

METHODS

A CD4+CD45RB(high) subpopulation of T cells was purified from the spleen of conventional BALB/c mice by magnetic separation (MACS) and transferred into immunodeficient SCID mice. Germ-free (GF) SCID mice or SCID mice monoassociated with Enterococcus faecalis, SFB (segmented filamentous bacteria), Fusobacterium mortiferum, Bacteroides distasonis, and in combination Fusobacterium mortiferum + SFB or Bacteroides distasonis + SFB were used as recipients. SCID mice were colonized by a defined cocktail of specific pathogen-free (SPF) bacteria. Mice were evaluated 8-12 weeks after the cell transfer for clinical and morphological signs of inflammatory bowel disease (IBD).

RESULTS

After the transfer of the CD4+CD45RB(high) T-cell subpopulation to SCID mice severe colitis was present in conventional animals and in mice colonized with a cocktail of SPF microflora plus SFB. Altered intestinal barrier in the terminal ileum of mice with severe colitis was documented by immunohistology using antibodies to ZO-1 (zona occludens).

CONCLUSIONS

Only SFB bacteria together with a defined SPF mixture were effective in triggering intestinal inflammation in the model of IBD in reconstituted SCID mice, while no colitis was detected in GF mice or in mice colonized either with SPF microflora or monoassociated only with SFB or colonized by Bacteroides distasonis + SFB or Fusobacterium mortiferum + SFB.

Inflammatory bowel disease: is the intestine a Trojan horse?

Inflammatory bowel disease (IBD) is a chronic relapsing inflammatory condition of the intestines that is clinically heterogenous. The cause(s) of IBD are currently unknown but the mechanisms of injury are immunological. Increasingly there is an emphasis on the study of the complex interactions at the interface of self and non-self--the gastrointestinal epithelial surface--in relationship to the pathogenesis of disease. There is mounting evidence that a lack of tolerance to the normal commensal flora of the intestine may underlie the disease pathogenesis. Several genetic loci that are markers of disease susceptibility have been identified. These loci map to areas of the genome that are concerned with antigen presentation or cytokine secretion and suggest a genetic heterogeneity that underlies the clinical differences. Overall a picture is emerging of defects in epithelial barrier function and, or immunoregulation leading to immune responses that are triggered or exaggerated by the antigenic components of the normal flora.

Oral administration of TNP-Lactobacillus conjugates in mice: a model for evaluation of mucosal and systemic immune responses and memory formation elicited by transformed lactobacilli

Safe live vector systems are being developed for oral delivery of antigens. A transformation system for indigenous Lactobacillus species of the gastrointestinal tract is described. Model systems were set up to evaluate immune responses. Orally administered trinitrophenylized (TNP) Lactobacillus were examined for their ability to induce immunological memory formation via determination of specific antibody titres in serum. We demonstrate a direct correlation between the level of systemic memory formation, as revealed by specific anti-TNP IgG serum antibodies, and the TNP substitution ratio of the Lactobacillus suspension used for oral priming. The specific IgG anti-TNP serum titres were comparable to or even higher than the titres of parental intraperitoneally primed animals. These results demonstrate the feasibility of using orally administered antigen-Lactobacillus as a future approach to vaccination.

Ultrastructure of filamentous microorganisms associated with zebra cyathostomes

Filamentous microorganisms were observed colonizing the cuticle of cyathostomes (Nematoda: Strongylidae) collected from the large intestine of Burchell's zebra (Equus burchelli antiquorum). Scanning (SEM) and transmission (TEM) electron microscopy revealed three filamentous microorganisms, designated as segmented, continuous multicellular, and helical. The segmented and continuous multicellular morphotypes each revealed a process of segmentation in their developmental stages, and those of the segmented filaments are demonstrated in this report. In contrast, the helical types of filaments appeared to be complexes of spiraling rodshaped organisms. In addition to these filaments, the cyathostome cuticle was also colonized by other smaller microorganisms.

Characterization of the microbial community colonizing the anal and vulvar pores of helminths from the hindgut of zebras

Scanning and transmission electron microscopy were used to examine the adherence and in situ morphology of the microbial community colonizing the anal and vulvar pores of the subfamily Cyathostominae (Nematoda: Strongylidae) from the colon of Burchell's zebra (Equus burchelli antiquorum). Two different morphological types of asporogenous rod were prominent in the microbial community. One was a thin, septate, filamentous organism (0.4 to 0.5 micron by 2 to 3 microns) with blunt ends, which was more prominent at the site of attachment. The other was a larger (1.8 to 2.4 microns by 5 to 10 microns) multicellular rod with round ends in the form of a trichome. Spiral- and vibrio-shaped bacteria were also present in the thin sections. The septate filaments were shown to contain a cell spacer similar to those described in Methanospirillum hungatei. Attachment to the cuticle was by means of an amorphous electron-dense material with fibrillar appearance and not by specialized holdfast segments. Ten isolates were obtained from a habitat-simulating medium on which a homogenate from the posterior region was plated. Antibodies were raised to whole cells of five rod-shaped isolates in rabbits and fluorescein isothiocyanate labeled. Positive bright-yellow fluorescence was obtained with one of the clostridial isolates. The results are discussed with reference to other bacteria with similar morphology, the nature of this unique interrelationship between the microbial community and its parasitic host inside the equine hindgut, and the possibility of biological control of parasitic helminths.

Lipoteichoic acids in Lactobacillus strains that colonize the mouse gastric epithelium

Extracts of cells of 22 strains of Lactobacillus species, and of fluids from cultures in a defined medium of two of the strains, were assayed by hemagglutination inhibition for lipoteichoic acids. A total of 10 of the preparations gave positive tests for the acids, including those from eight strains known to adhere to the keratinized squamous epithelium of the mouse stomach. These findings are consistent with an hypothesis that lactobacilli colonize the epithelial surface via adhesive interaction with the keratinized cells mediated by macromolecular complexes containing lipoteichoic acids.

Mucus colonization as a determinant of pathogenicity in intestinal infection by Campylobacter jejuni: a mouse cecal model

Human isolates of the intestinal pathogen Campylobacter jejuni have been shown to colonize mucus on the outer surface and deep within the intestinal crypts of gnotobiotic or germfree mice. The cecal crypts are preferentially colonized. A model of mucus colonization by C. jejuni in the mouse cecum has been developed, using antibiotic- and magnesium sulfate-treated specific-pathogen-free animals. These spiral-shaped bacteria colonize the mucus in a similar manner to the normal spiral-shaped microbiota. No evidence of adhesion to the intestinal surface was found with a wide variety of microscopic techniques. The campylobacters were seen to be highly motile in living preparations of gut tissue and rapidly tracked along intestinal mucus. Just as many of the normal spiral-shaped bacteria of intestinal surfaces can achieve close association with the epithelium through mucus association and do not adhere to the surface, C. jejuni colonizes the intestinal mucosa via mucus colonization. Thus, a major determinant of pathogenicity in intestinal infection with C. jejuni is proposed to be an ability to colonize intestinal mucus. The possession of specific adhesins is unlikely to be a significant determinant of pathogenicity. Better understanding of the mechanism of mucus association and the properties of the bacterium that are responsible will provide a basis for the rational selection of preventative measures. The model of mucus association in adult antibiotic-treated mice provides an opportunity for colonization studies with variant organisms and immunization studies.

Prevention of adhesion by indigenous bacteria to rabbit cecum epithelium by a barrier of microvesicles

None of 74 strains of anaerobic bacteria cultured from the mucosal epithelial interface of the rabbit cecum adhered to isolated brush borders in experiments in which enteropathogenic Escherichia coli RDEC-1 was used as an adherent control. Scanning electron microscopy of the surfaces of the cecal epithelia confirmed that few organisms were in contact with the villus surface, but transmission electron microscopy revealed a layer of microvesicles up to 50 nm in diameter between the microvilli and mucous gel. The evidence indicates that there is no significant epithelium-adherent flora in the cecum but that a microvesicular layer could contribute significantly to prevention of adherence by both normal and potentially pathogenic bacteria.