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T Midtvedt

Publications and source records attributed to T Midtvedt.

At least 55 records · Page 3Linked to original sources
PubMed1998

Creating and maintaining the gastrointestinal ecosystem: what we know and need to know from gnotobiology.

Studying the cross talk between nonpathogenic organisms and their mammalian hosts represents an experimental challenge because these interactions are typically subtle and the microbial societies that associate with mammalian hosts are very complex and dynamic. A large, functionally stable, climax community of microbes is maintained in the murine and human gastrointestinal tracts. This open ecosystem exhibits not only regional differences in the composition of its microbiota but also regional differences in the differentiation programs of its epithelial cells and in the spatial distribution of its component immune cells. A key experimental strategy for determining whether "nonpathogenic" microorganisms actively create their own regional habitats in this ecosystem is to define cellular function in germ-free animals and then evaluate the effects of adding single or several microbial species. This review focuses on how gnotobiotics-the study of germ-free animals-has been and needs to be used to examine how the gastrointestinal ecosystem is created and maintained. Areas discussed include the generation of simplified ecosystems by using genetically manipulatable microbes and hosts to determine whether components of the microbiota actively regulate epithelial differentiation to create niches for themselves and for other organisms; the ways in which gnotobiology can help reveal collaborative interactions among the microbiota, epithelium, and mucosal immune system; and the ways in which gnotobiology is and will be useful for identifying host and microbial factors that define the continuum between nonpathogenic and pathogenic. A series of tests of microbial contributions to several pathologic states, using germ-free and ex-germ-free mice, are proposed.

Animals↗
PubMed1997

Regional phenotypic specialization of intraepithelial lymphocytes in the rat intestine does not depend on microbial colonization.

Recent studies in mice and humans have provided evidence for regional specialization of gut intraepithelial lymphocytes (IEL). Here the authors report striking regional variability in the composition of IEL in rat small and large intestine. Two-colour immunofluorescence in situ analysis showed that the distribution of the CD3+ and CD3- IEL subpopulations varied, the proportion of T cells (CD3+) being higher in the ileum than in the jejunum and smallest in the colon. These differences were explained by variable numbers of the T-cell receptor (TCR)alpha/beta + (both CD8+ and CD4+) but not the TCR gamma/delta + subset. Moreover, the various IEL subpopulations showed distinct intraepithelial distribution patterns with CD4+ and CD8 alpha beta + T cells situated near the lamina propria, while CD3- IEL were located preferentially towards the adluminal part of the epithelium. Regional phenotypic variation did not depend on intestinal colonization because analogous results were obtained in germ-free rats. Conventionalization nevertheless caused a marked relative increase of small intestinal TCR alpha/beta + but not TCR gamma/delta + IEL. This increase was more sustained in the jejunum than ileum and eventually reduced the phenotypic IEL differences between the two sites. By contrast, microbial colonization of the colon induced only a transient increase of intraepithelial TCR alpha/beta + cells with no permanent phenotypic alterations. Both CD3+ and CD3- IEL contained subpopulations that expressed NKR-P1 independent of intestinal colonization. These results demonstrate phenotypic specialization of IEL at different levels of the gut and suggest that the indigenous flora is not essential to this end.

Animals↗
PubMed1997

Germ-free and conventional animal models for intestinal carbohydrate disposition.

Under conventional (CONV) conditions, the microbial flora is capable of breaking down most dietary derived carbohydrates as well as complex carbohydrates (glycolipids, glycoproteins, etc.) from the host. The major end products of these processes are short-chain fatty acids (SCFAs). In non-ruminants, most of the fermentation takes place in the large bowel. In ruminants, however, most acids are formed more proximal in the gastrointestinal (GI) tract. These microbial derived products may influence upon many host related functions, locally in the GI tract as well as elsewhere in the body. In germ-free (GF) animals, neglectable amounts of SCFAs are found in faeces. Parallel studies in GF and CONV animals given a standardized diet and ex-GF animals, receiving the same diet and mono/poly-associated with known microbial species, represent excellent models for answering such questions as (i) what can the microbes do? and (ii) what have the microbes done? These models allow detailed studies of the complex interplay between the host, his diet and his GI flora.

Animals↗
PubMed1997

Sulphasalazine, olsalazine and sulphapyridine induce mitogenic actions in the rat intestinal epithelium.

Our aim was to study the influence of sulphasalazine (SASP), olsalazine (ADS) and sulphapyridine (SP) on the cell kinetics of the intestinal epithelium in conventional rats. Groups of rats were treated with SASP, ADS or SP for 9 days. After an intraperitoneal injection of a metaphase blocker, the rats were killed and the jejunum, ileum and colon were examined in histological sections by means of the cumulative mitotic index (MI), growth fraction and number of cells in crypts and villi. SP increased both the MI in the jejunum, ileum and colon and the number of crypt cells (p < 0.05 vs controls). In contrast, SASP and ADS increased the MI only in the colonic epithelium (p < 0.05 vs controls). The growth fraction was essentially unaffected. Our results suggest that SASP, SP and ADS have a selective compartment-dependent proliferative action on the epithelium of the intestinal tract.

Aminosalicylic Acids↗
PubMed1997

Escherichia coli K5 capsule expression enhances colonization of the large intestine in the gnotobiotic rat.

The role of capsule expression in the capacity of Escherichia coli to colonize in the large intestinal environment was studied in a gnotobiotic rat model. The rats were given perorally a mixture of two mutant strains differing in K5 expression. After 2 weeks, the rats were sacrificed, and subsequently intestinal contents, intestinal mucosae, and mesenteric lymph nodes were homogenized and bacterial numbers were quantified. Two E. coli mutant pairs were used, the first pair (972-998) lacking the O-specific side chain and the second pair (973-997) carrying the O75 lipopolysaccharide. The K5+ mutants established themselves at a higher level than the K5- mutants (10(9) versus 10(6) CFU/g [P < 0.001] for the first pair and 10(9) versus 10(8) CFU/g [P < 0.01] for the second pair, respectively). The results were confirmed by serology showing a K5+ phenotype for practically all isolates. The bacterial population associated with the mucosa was similar to that in the luminal contents with respect to the proportions of the respective mutants, and translocation occurred in numbers proportional to the intestinal population densities of the respective mutants. All mutants were able to express type 1 as well as P fimbriae. After colonization, the expression of P fimbriae remained high whereas only a minority of the isolates expressed type 1 fimbriae. The results suggest that capsule expression and P fimbriae enhance intestinal colonization by E. coli and that these virulence factors, by increasing bacterial densities in the intestine, secondarily increase translocation.

Adhesins, Escherichia coli↗
PubMed1997

Endogenous prostaglandins and microflora modulate DNA synthesis and neuroendocrine peptides in the rat gastrointestinal tract.

BACKGROUND: Previous studies suggest that E2 prostaglandins and the microflora may participate in the regulation of endocrine cells and of gastrointestinal cell kinetics. Our aim is to examine the actions of endogenous prostaglandins and of the microflora on gastrointestinal cell proliferation and tissue levels of neuroendocrine peptides. METHODS: Germfree and ex-germfree rats were treated with subcutaneous placebo or 1.5 mg/kg indomethacin for 3 days. All rats were labeled with 3H-methyl-thymidine, and biopsy specimens from different parts of the gastrointestinal tract were processed for autoradiography. DNA synthesis was estimated by the labeling index, except in the oxyntic mucosa, where the total number of labeled cells present in 7.5 mm mucosa was used. The concentration of neuroendocrine peptides was determined by radioimmunoassay. RESULTS: In the germfree rat, indomethacin reduced DNA synthesis in the fundus, duodenum, and proximal jejunum (P < 0.05) and the number of villous cells throughout the small intestine (P < 0.05). Exposure to microflora increased DNA synthesis in the proximal and distal jejunum, ileum, and colon (P < 0.05 versus germfree controls) and the number of crypt cells in the distal small intestine and colon (P < 0.05) and reduced the number of villous cells in the small intestine (P < 0.05) but did not affect tissue concentrations of neuroendocrine peptides. Indomethacin increased the concentration of somatostatin in the stomach, duodenum, and colon of germfree rats (P < 0.001), the concentration of calcitonin gene-related peptide (CGRP) and enteroglucagon in the proximal and distal jejunum and ileum (P < 0.001), and the concentration of glucagon in the colon (P < 0.05). The concentrations of somatostatin, CGRP, and glucagon were lower in indomethacin-treated ex-germfree rats than in indomethacin-treated germfree rats (P < 0.01). CONCLUSIONS: Indomethacin selectively reduced DNA synthesis in the upper gastrointestinal tract of germfree rats, indicating a basal stimulatory role for endogenous prostaglandins on cell proliferation. Endogenous prostaglandins modulate synthesis or release of gastrointestinal neuroendocrine peptides. Somatostatin may mediate indomethacin-induced reduction of DNA synthesis. The microflora stimulates cell proliferation and influences tissue levels of neuroendocrine peptides in a manner opposite to that of indomethacin.

Animals↗
PubMed1996

A model of host-microbial interactions in an open mammalian ecosystem.

The maintenance and significance of the complex populations of microbes present in the mammalian intestine are poorly understood. Comparison of conventionally housed and germ-free NMRI mice revealed that production of fucosylated glycoconjugates and an alpha1, 2-fucosyltransferase messenger RNA in the small-intestinal epithelium requires the normal microflora. Colonization of germ-free mice with Bacteroides thetaiotaomicron, a component of this flora, restored the fucosylation program, whereas an isogenic strain carrying a transposon insertion that disrupts its ability to use L-fucose as a carbon source did not. Simplified models such as this should aid the study of open microbial ecosystems.

Animals↗
PubMed1996

Microbial colonization influences composition and T-cell receptor V beta repertoire of intraepithelial lymphocytes in rat intestine.

Studies in mice have shown that the composition of intestinal intraepithelial lymphocytes (IEL) may be markedly altered by gut microbial colonization. Such modulation was studied in a rat model by the use of germ-free and conventionalized animals from which IEL from the small intestine were isolated and analysed by flow cytometry. Conventionalization caused expansion as well as phenotypic alterations of T-cell receptor (TCR) alpha/beta + IEL in that the proportions of CD4+ and CD8 alpha beta + TCR alpha/beta + cells were increased, while the double negative (CD4- CD8-) fraction was reduced. microbial colonization also influenced the TCR V beta repertoire of CD8+ IEL in that the proportions of V beta 8.2+ and V beta 10+ cells were increased, whereas V beta 8.5+ and V beta 16+ cells were relatively decreased. Moreover, conventionalization influenced the levels of TCR cell surface expression in the same V beta subsets. Three-colour flow-cytometric analysis demonstrated that skewing of the V beta repertoire was most pronounced in the CD8 alpha alpha + subset, although the numerical increase of IEL mainly included the CD8 alpha beta + subset. In contrast to IEL, the TCR V beta repertoire in mesenteric lymph nodes was unchanged after intestinal colonization. These results confirm that TCR alpha/beta + IEL subpopulations respond dynamically to the microbial gut flora and suggest that their V beta repertoire can be shaped by luminal microbial antigens.

Animals↗
PubMed1995

[Microbiology and ecology--the microbe aspect].

Invisible microbes play very important roles in all ecosystems. Living generally in harsh and seemingly inhospitable places all around, they reveal a remarkable potential and resilience of life. In all microbial ecosystems, antimicrobial substances, as antibiotics, are of crucial regulatory importance. In modern human and veterinarian medicine, about 50 million kilos of potent antibiotics are used every year. Some of these substances are very persistent in the ecosystem, i.e. they remain in the natural environment for a very long time. Now the microbial empire is striking back, and increasing resistance towards antibiotics is becoming a global problem. The need for a proper future strategy is underlined.

Anti-Bacterial Agents↗
PubMed1995

Intestinal microbial bile acid transformation in healthy infants.

Following the establishment of functionally active intestinal flora in three healthy Swedish children from birth up to 24 months of age, we investigated the development of different 24-carbon bile acids. The fecal bile acids were group-separated into unconjugated, glycine-conjugated, taurine-conjugated, and sulfated, so that we could follow the changes between the different fractions of conjugates. In meconium, most (55-63%) of the bile acids were conjugated with taurine; only 11-32% were conjugated with glycine. Deconjugation was the first sign of intestinal microbial activity on the bile acids. Already at 1 month of age, most of the bile acids were deconjugated; among the conjugated bile acids, the glycine-conjugated dominated over the taurine-conjugated. An unidentified conjugate of cholic and chenodeoxycholic acids (C, CDC) that separated with the sulfated bile acids was found. The unconjugated bile acids and those that arose from hydrolysis of existing conjugates were separated and identified by gas-liquid chromatography coupled to mass spectrometry (GC-MS). Twenty-nine different bile acids were identified. In meconium, 16 different bile acids were identified. C and CDC were identified in all samples. The bile acid pattern changed during the course of the study. Many of the identified bile acids were only found in one or a few of the analyzed samples, and sometimes only in samples from one child. 6 alpha-hydroxylated bile acids, probably not microbially synthesized, were present at high percentages in the children.(ABSTRACT TRUNCATED AT 250 WORDS)

Bifidobacterium↗
PubMed1995

Role of Escherichia coli P fimbriae in intestinal colonization in gnotobiotic rats.

Adherence via P fimbriae is associated with long-term persistence of Escherichia coli in the human large intestine, but a causal relationship has not been proven. In the present study, germfree rats were colonized with a mixture of two isogenic E. coli strains, one P fimbriated and the other type 1 fimbriated. Both types of fimbriae conferred adherence to rat colonic epithelial cells. With two mutant strains from a pyelonephritogenic isolate of serotype O75:K5:H-, the P-fimbriated strain 824 attained much higher numbers than its type 1-fimbriated counterpart when colonized in vivo for 2 weeks (10(10) versus 10(6) bacteria per g, respectively; P < 0.0001). The expression of P fimbriae by 824 was also retained during colonization. With transformant isogenic strains obtained from a normal fecal isolate incapable of phase variation, no benefit of P fimbriae was seen and most bacteria lost their plasmids during in vivo colonization. When the pyelonephritogenic mutant and fecal transformant strains were combined, the former colonized at high levels while the latter were suppressed. In contrast, no suppression was seen when the transformant E. coli strains colonized in combination with Lactobacillus acidophilus or Peptostreptococcus sp. The results indicate that P fimbriae, but also other bacterial traits linked to uropathogeneicity, could play an important role for persistence in the gut normal microbiota. Neither P nor type 1 fimbriae seemed to contribute to the ability to translocate to the mesenteric lymph nodes.

Animals↗
PubMed1994

Paneth cell differentiation in the developing intestine of normal and transgenic mice.

Paneth cells represent one of the four major epithelial lineages in the mouse small intestine. It is the only lineage that migrates downward from the stem-cell zone located in the lower portion of the crypt of Lieberkühn to the crypt base. Mature Paneth cells release growth factors, digestive enzymes, and antimicrobial peptides from their apical secretory granules. Some of these factors may affect the crypt stem cell, its transit-cell descendants, differentiating villus-associated epithelial lineages, and/or the gut microflora. We used single and multilabel immunocytochemical methods to study Paneth cell differentiation during and after completion of gut morphogenesis in normal, gnotobiotic, and transgenic mice as well as in intestinal isografts. This lineage emerges coincident with cytodifferentiation of the fetal small intestinal endoderm, formation of crypts from an intervillus epithelium, and establishment of a stem-cell hierarchy. The initial differentiation program involves sequential expression of cryptdins, a phospholipase A2 (enhancing factor), and lysozyme. A dramatic increase in Paneth cell number per crypt occurs during postnatal days 14-28, when crypts proliferate by fission. Accumulation of fucosylated and sialylated glycoconjugates during this period represents the final evolution of the lineage's differentiation program. Establishment of this lineage is not dependent upon instructive interactions from the microflora. Transgenic mice containing nucleotides -6500 to +34 of the Paneth cell-specific mouse cryptdin 2 gene linked to the human growth hormone gene beginning at its nucleotide +3 inappropriately express human growth hormone in a large population of proliferating and nonproliferating cells in the intervillus epithelium up to postnatal day 5. Transgene expression subsequently becomes restricted to the Paneth cell lineage in the developing crypt. Cryptdin 2 nucleotides -6500 to +34 should be a useful marker of crypt morphogenesis and a valuable tool for conducting gain-of-function or loss-of-function experiments in Paneth cells.

Animals↗
PubMed1994

Ca(2+)-dependent and Ca(2+)-independent exhaled nitric oxide, presence in germ-free animals, and inhibition by arginine analogues.

Nitric oxide (NO) was detected by chemiluminescence in exhaled air from awake humans, anaesthetized rabbits, guinea pigs, germ-free rats and conventional rats. Rabbits exhibited the highest concentrations, followed by guinea pigs, humans and rats. There was no significant difference between germ-free rats and control rats. The authenticity of NO was confirmed in cold-trap experiments. Intravenous administration of inhibitors of NO synthase (0.01-300 mg kg-1) to guinea pigs dose dependently reduced NO concentrations in exhaled air with the following potency order: L-N omega-nitro-arginine-methylester > asymmetric NG,NG-dimethyl-L-arginine-dihydrochloride = L-NG-mono-methyl -arginine = L-N5- (1-iminoethyl)-ornithine = aminoguanidine > L-canavanine. The effect of the NO synthase inhibitors was partly or fully reversed by L-arginine (1 g kg-1 i.v.), and L-arginine per se induced a significant increment of NO in exhaled air. In rats, L-N omega-nitro-arginine-methylester was considerably less potent than in guinea pigs. The concentration of NO in exhaled air increased 3-fold when changing from in situ blood auto-perfusion of rabbit lungs to in situ perfusion with saline medium. Addition of L-N omega-nitro-arginine-methylester to the saline perfusion medium evoked a reduction of NO concentrations in the air from the ventilated perfused lungs. Perfusion of lungs with Ca(2+)-free medium induced significant decrements in NO concentrations in exhaled air, an effect partly reversed upon reintroducing Ca2+ into the medium. In conclusion, NO was detected in exhaled air from humans and animals by chemiluminescence.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1994

Intestinal microflora stimulates myoelectric activity of rat small intestine by promoting cyclic initiation and aboral propagation of migrating myoelectric complex.

Microbial modulation of myoelectric activity in small intestine was studied. Germ-free male Sprague-Dawley rats were equipped with bipolar electrodes from the duodenojejunal junction to the midpoint of small intestine. Prior to and one week after introduction of conventional intestinal microflora, 32 +/- 5% and 61 +/- 5% (mean +/- SE), respectively, of activity fronts of the migrating myoelectric complex reached the midpoint (P < 0.05), and the interval between activity fronts in proximal jejunum was reduced from 31.2 +/- 2.0 min to 17.5 +/- 0.8 min, respectively (P < 0.01). The pattern of propagation was more regular after conventionalization. Slow-wave frequency in proximal jejunum was 38.5 +/- 1.2/min in germ-free rats and 43.0 +/- 0.8/min in conventional rats (P < 0.01), but introduction of microflora failed to increase the frequency in germ-free rats. The frequency of spike potentials succeeding jejunal infusion of 5 ml of 12.5% glucose remained unchanged after conventionalization. Statistical analyses showed that the interval between activity fronts varied mainly within rats, whereas the propagation velocity showed statistically significant variability between rats (P < 0.01), regardless of intestinal microflora. Luminal control by the resident microflora is important for physiological cycling and aboral propagation of the migrating myoelectric complex, but seems to be of no major consequence for postprandial myoelectric response.

Action Potentials↗
PubMed1994

Microflora modulates endocrine cells in the gastrointestinal mucosa of the rat.

BACKGROUND/AIMS: Gastrointestinal peptides and biogenic monoamines participate in the regulation of gastrointestinal functions. The aim of this study was to examine the influence of the microflora on the distribution of endocrine cells and on the release of gastrointestinal peptides. METHODS: A quantitative morphological study using stereological methods was performed in gastrointestinal sections of conventional and germ-free rats. Tissue and plasma concentrations of peptides were measured. RESULTS: The total volumes of gastrin- and serotonin-immunoreactive cells were significantly increased in the gastric mucosa of germfree rats (P < 0.05), as well as the total volumes of serotonin- and motilin-immunoreactive cells in the ileum (P < 0.05) and serotonin-immunoreactive cells in the colonic mucosa (P < 0.05). The tissue concentration of somatostatin was significantly higher in the jejunum (P < 0.05) and lower in the ileum of germfree rats than in controls (P < 0.05). Plasma glucagon was significantly increased in germfree rats (P < 0.05). The total volume of the fundic mucosa was enlarged in germfree rats (P < 0.05), whereas the total volume, the mucosal thickness, and the number of crypt cells of the colonic mucosa were significantly reduced in these rats compared with controls (P < 0.05). CONCLUSIONS: Our findings suggest that the intraluminal microflora influences the release of biologically active peptides and that it participates in the regulation of gastrointestinal endocrine cells and the epithelial structure.

Animals↗
PubMed1994

Intestinal microflora enhances formation of DNA adducts following administration of 2-NF and 2-AAF.

2-Nitrofluorene (NF) is found in the environment mainly due to incomplete combustion, as in vehicles. The major class of metabolites in vivo in rats after oral administration is the reduced and acetylated metabolites, e.g. derivatives of 2-acetylaminofluorene (AAF). The intestinal microflora reduces the nitro function to an amine which is further metabolized via acetylation and hydroxylations. In this study, NF and AAF were orally administered to germ-free and conventional rats with the aim of studying DNA adduct formation in different tissues with the 32P-post-labelling assay. Chromatographic detection was performed with TLC and on-line 32P detection after HPLC separation of DNA adducts. The major (95%) DNA adduct formed was dG-C8-AF for both NF and AAF. The potency to form DNA adducts successively declined with the combinations conventional/AAF, germ-free/AAF, conventional/NF and germ-free/NF. The DNA adduct dG-C8-AF was detected in all four tissues that were analysed, e.g. liver, kidney, lung and heart. The presence of intestinal microflora enhanced the formation of DNA adducts in the tissues studied.

2-Acetylaminofluorene↗
PubMed1994

Establishment of a mucin-degrading intestinal microflora during the first two years of human life.

The establishment of a mucin-degrading intestinal microflora was followed in 30 healthy Swedish children by agar gel electrophoresis of fecal samples taken at 0, 1, 3, 6, 9, 12, 15, 18, 21, and 24 months of age. At 3 months, 18 children showed a limited degree of mucin degradation, while 12 children showed no degradation. In children exclusively breast-fed for at least 4 months, mucin degradation was initiated significantly later than in children who received formula, with or without breast milk, by 1 month of age. Complete degradation of mucin was seen in 21 children after 1 year of age and in all children at 2 years. A positive correlation between increasing age and increased degradation of mucin was found between birth and 1 month and between 6 and 9 months, after standardization for the period of exposure to foods other than breast milk.

Anti-Bacterial Agents↗