Establishment of the gut microbiota in Western infants

In adult individuals, the intestinal microbiota comprises several hundred, mostly anaerobic, bacterial species. This complex ecosystem is formed through the successive establishment of different bacteria in infancy and early childhood. Facultative and aerotolerant bacteria establish first, followed by more and more strict anaerobes. The bacteria derive from different sources and the colonization pattern is influenced by delivery mode and environmental factors. Commensal microbes provide the major drive for maturation of the immune system. Increased hygiene appears to have changed the gut flora of Western infants, which may affect the risk of developing immune mediated diseases.

CONCLUSION

It is clear that the process of infant colonization needs to be studied further, since composition of the microbiota may impact on child health.

The normal Lactobacillus flora of healthy human rectal and oral mucosa

The Lactobacillus flora of the rectal and oral mucosa was sampled from 42 healthy volunteers. Species identification was carried out by numerically comparing API 50CH fermentation patterns with type strains, using an SJ-similarity cut-off level of 79%. For the largest groups, identity was further confirmed by DNA-DNA hybridizations against the type strain of the species. Seventeen lactobacilli clusters were defined, of which most were found both on rectal and oral mucosa. The largest taxa were Lactobacillus plantarum, Lact. rhamnosus and Lact. paracasei ssp. paracasei, which were isolated from 52%, 26% and 17% of the individuals, respectively. Most isolates were tested for their capacity to adhere to the human colonic cell line HT-29 in the absence and presence of methyl-alpha-D-mannoside. Mannose-sensitive adherence to HT-29 cells was encountered in two-thirds of the Lact. plantarum isolates, but infrequently among isolates of other taxa. The results suggest that Lact. plantarum is a major colonizer of the human gastrointestinal mucosa, and that its capacity to adhere to mannose-containing receptors may be of some ecological importance.

Secretory immunoglobulin A carries oligosaccharide receptors for Escherichia coli type 1 fimbrial lectin

Type 1 fimbriae with mannose-specific lectins are widely distributed among members of the family Enterobacteriaceae and confer the ability to attach to a range of host cells, including colonic epithelial cells. The mucosal surfaces are protected by secretory immunoglobulin A (IgA), which agglutinates microorganisms and prevents their attachment to host epithelial cells. This action has been attributed to a specificity of the antigen-combining site of mucosal immunoglobulins for bacterial and viral surface components. Here, we report a novel mechanism for the antibacterial effect of secretory IgA. Secretory IgA and IgA myeloma proteins, especially those of the IgA2 subclass, were shown to possess carbohydrate receptors for the mannose-specific lectin of type 1-fimbriated Escherichia coli. The presence of the high-mannose oligosaccharide chain Man alpha 1-6(Man alpha 1-3)Man alpha 1-6(Man alpha 1-3)Man beta 1-4GlcNAc beta 1-4GlcNAc correlated with binding activity. The interaction between bacterial mannose-specific lectins and IgA receptor oligosaccharide resulted in agglutination of the bacteria and in inhibition of bacterial attachment to colonic epithelial cells. Thus, this interaction could form the basis for a broad antibacterial function of secretory IgA against enterobacteria regardless of the specificity of antibody molecules.

Gram-positive bacteria are potent inducers of monocytic interleukin-12 (IL-12) while gram-negative bacteria preferentially stimulate IL-10 production

Interleukin-10 (IL-10) and IL-12 are two cytokines secreted by monocytes/macrophages in response to bacterial products which have largely opposite effects on the immune system. IL-12 activates cytotoxicity and gamma interferon (IFN-gamma) secretion by T cells and NK cells, whereas IL-10 inhibits these functions. In the present study, the capacities of gram-positive and gram-negative bacteria to induce IL-10 and IL-12 were compared. Monocytes from blood donors were stimulated with UV-killed bacteria from each of seven gram-positive and seven gram-negative bacterial species representing both aerobic and anaerobic commensals and pathogens. Gram-positive bacteria induced much more IL-12 than did gram-negative bacteria (median, 3,500 versus 120 pg/ml at an optimal dose of 25 bacteria/cell; P < 0.001), whereas gram-negative bacteria preferentially stimulated secretion of IL-10 (650 versus 200 pg/ml; P < 0.001). Gram-positive species also induced stronger major histocompatibility complex class II-restricted IFN-gamma production in unfractionated blood mononuclear cells than did gram-negative species (12,000 versus 3,600 pg/ml; P < 0.001). The poor IL-12-inducing capacity of gram-negative bacteria was not remediated by addition of blocking anti-IL-10 antibodies to the cultures. No isolated bacterial component could be identified that mimicked the potent induction of IL-12 by whole gram-positive bacteria, whereas purified LPS induced IL-10. The results suggest that gram-positive bacteria induce a cytokine pattern that promotes Th1 effector functions.

A mannose-specific adherence mechanism in Lactobacillus plantarum conferring binding to the human colonic cell line HT-29

Two Lactobacillus plantarum strains of human intestinal origin, strains 299 (= DSM 6595) and 299v (= DSM 9843), have proved to be efficient colonizers of the human intestine under experimental conditions. These strains and 17 other L. plantarum strains were tested for the ability to adhere to cells of the human colonic cell line HT-29.L.plantarum 299 and 299v and nine other L. plantarum strains, including all six strains that belong to the same genetic subgroup as L. plantarum 299 and 299v, adhered to HT-29 cells in a manner that could be inhibited by methyl-alpha-D-mannoside. The ability to adhere to HT-29 cells correlated with an ability to agglutinate cells of Saccharomyces cerevisiae and erythrocytes in a mannose-sensitive manner and with adherence to D-mannose-coated agarose beads. L. plantarum 299 and 299v adhered to freshly isolated human colonic and ileal enterocytes, but the binding was not significantly inhibited by methyl-alpha-D-mannoside. Periodate treatment of HT-29 cells abolished mannose-sensitive adherence, confirming that the cell-bound receptor was of carbohydrate nature. Proteinase K treatment of the bacteria also abolished adherence, indicating that the binding involved protein structures on the bacterial cell surface. Thus, a mannose-specific adhesin has been identified in L. plantarum; this adhesin could be involved in the ability to colonize the intestine.

Lactobacilli from human gastrointestinal mucosa are strong stimulators of IL-12 production

Interaction of macrophages with bacteria is a stimulus for production of cytokines such as IL-10 and IL-12. IL-12 stimulates T cell and natural killer (NK) cell cytotoxicity and interferon-gamma (IFN-gamma) production. IL-10 opposes the T cell-stimulating action of IL-12, decreases the release of proinflammatory cytokines from macrophages, and stimulates B cells. We have studied the capacity of human intestinal isolates from the three Lactobacillus species dominating on the human gastrointestinal mucosa, L. plantarum, L. rhamnosus and L. paracasei ssp. paracasei, to induce production of IL-10 and IL-12 from human blood mononuclear cells, or monocytes. Whole killed lactobacilli were potent stimulators of IL-12 over a wide range of bacterial concentrations. Lactobacillus paracasei gave the highest levels of IL-12 (1.5 ng/ml in response to 5 x 106 bacteria/ml), roughly 10 times more than obtained by stimulation with L. rhamnosus or L. plantarum. Escherichia coli induced on average < 50 pg/ml of IL-12 regardless of the bacterial concentration used. The secretion of free p40 subunit IL-12 followed the same pattern as the secretion of p70 (bioactive IL-12) with regard to the efficiency of different bacteria as stimulators. Escherichia coli was the most efficient trigger of IL-10 production, inducing 0.5 ng/ml IL-10 after stimulation with 5 x 106 bacteria/ml. Lactobacillus rhamnosus induced the highest levels of IL-10 among the lactobacilli (0.5 ng/ml) compared with 0.1 ng/ml evoked by L. plantarum or L. paracasei, but 10 times more bacteria were required for optimal stimulation than with E. coli. When neutralizing anti-IL-10 antibodies were added to the cultures, the IL-12-inducing capacity of L. rhamnosus was increased markedly, while that of E. coli remained low. The results show that mucosa-associated lactobacilli can be potent stimulators of IL-12, and thus potentially of cell-mediated immunity, if they pass over the gut epithelial barrier and interact with cells of the gut immune system.

Intestinal colonization with Enterobacteriaceae in Pakistani and Swedish hospital-delivered infants

Rectal cultures from Swedish and Pakistani hospital-delivered newborn infants were analysed regarding the early acquisition of enterobacteria. Swedish infants were delivered vaginally, Pakistani infants were delivered either vaginally or by caesarean section. The Swedish infants were all breast-fed, whereas breastfeeding was incomplete and often started late among the Pakistani infants. Both groups of Pakistani infants were more rapidly colonized with enterobacteria than were the Swedish infants. Cultures from Swedish infants seldom yielded more than one kind of enterobacteria; E. coli and Klebsiella were most frequently isolated. E. coli dominated in both Pakistani groups, but especially caesarean section delivered infants were in addition often colonized with Proteus, Klebsiella, Enterobacter or Citrobacter species. Breastfeeding from the first day of life reduced colonization with Klebsiella/Enterobacter/Citrobacter. The results suggest that environmental exposure, delivery mode and early feeding habits all influence the early intestinal colonization with enterobacteria.

Breast feeding and the intestinal microflora of the infant--implications for protection against infectious diseases

Human breast milk contains an array of factors with anti-infectious potential, such as immunoglobulins (especially secretory IgA), oligosaccharides and glycoproteins with anti-adhesive capacity, and cytokines. Breast-feeding is associated with protection from the following infections or infection-related conditions: gastroenteritis, upper and lower respiratory tract infection, acute otitis media, urinary tract infection, neonatal septicaemia and necrotizing enterocolitis. Some of the protective effects may derive from an altered mucosal colonization pattern in the breast-fed infant. In other instances breast-fed infants develop less symptoms to the same microbe which causes disease in the bottle-fed infant. An example of an altered colonization pattern is that breast-fed infants have less P-fimbriated, but more type 1-fimbriated E. coli. This may protect against urinary tract infection in the breast-fed infant since P. fimbriae are the major virulence factor for urinary tract infection. An example of changed consequences of the same microbial colonization is that secretory IgA in the breast-milk protects very efficiently from translocation of intestinal bacteria across the gut mucosa by coating intestinal bacteria and blocking their interaction with the epithelium. This mechanism may protect the infant from septicaemia of gut origin and, possibly, necrotizing enterocolitis. Breast-milk is also highly anti-inflammatogenic and contains hormone like factors which counteract diarrhea. Thus, breast-fed infants may be colonized by recognized diarrheal pathogens and still remain healthy. Due to a less virulent intestinal microflora and decreased translocation breast-fed infants will obtain less stimuli for the gut immune system, resulting, in e.g., lower salivary IgA antibody titres.

Attachment of Escherichia coli via mannose- or Gal alpha 1----4Gal beta-containing receptors to human colonic epithelial cells

The role of bacterial adhesion for the maintenance of the large-intestinal microflora has not been established. In this study, colonic cells from the adenocarcinoma cell line HT-29 or from surgical specimens were tested for the ability to bind Escherichia coli. The E. coli strains were manipulated by transformation or by mutagenesis to express either mannose-specific type 1 fimbriae (strains 506 MS and HU742) or Gal alpha 1----4Gal beta-specific P fimbriae (506 MR and HU824). Binding to HT-29 cells was seen with strains of either receptor specificity and was inhibited by alpha-methyl mannoside or globotetraosylceramide (GalNAc beta 1----3Gal alpha 1----4Gal beta 1----4Glc-ceramide), respectively. The Gal alpha 1----4Gal beta-specific strains interacted with a loosely surface-associated substance, which was sensitive to mechanical treatment and incubation at 37 degrees C, while the mannose-specific strains bound both directly to the cell and to the loosely associated substance. Isolated colonic epithelial cells bound the mannose-specific bacteria in high numbers, while the attachment of the Gal alpha 1----4Gal beta-specific strains depended on the elution method. Cells eluted sequentially with magnetic stirring were unable to bind the Gal alpha 1----4Gal beta-specific bacteria, while elution by a more gentle method resulted in binding of these strains to material loosely associated with the epithelial cells. Thus, the binding pattern of isolated colonic epithelial cells paralleled that of the HT-29 cell line. Conceivably, binding to mannose- and Gal alpha 1----4Gal beta-containing receptors could contribute to the maintenance of E. coli in the human large intestine.

Resident colonic Escherichia coli strains frequently display uropathogenic characteristics

Bacterial factors associated with long-term persistence in the colon have not been defined. Individual Escherichia coli strains in the colonic flora of 13 schoolgirls with asymptomatic bacteriuria were identified by electromorphic typing of chromosomally encoded enzymes and defined as resident or transient. The strains were characterized as to serotype, receptor specificity, and adherence to the human colonic epithelial cell line HT-29. Colonic resident strains expressed P fimbriae, adhered to colonic epithelial cells via a mannose-resistant mechanism, and expressed the uropathogenic serotypes O1, O2, O6, O7, O18, O25, or O75 more often than did the transient strains, which were often nontypeable. The serotype and hemagglutination pattern were generally retained during intestinal carriage, in contrast to the loss of such properties upon prolonged colonization of the urinary tract. P fimbriae with Gal alpha 1----4Gal beta-specific adherence may, in fact, have evolved to increase persistence in the colon.

Immunomodulatory effects of Lactobacillus plantarum colonizing the intestine of gnotobiotic rats

We have studied the effect of the probiotic strain Lactobacillus plantarum 299v on the immune functions of gnotobiotic rats. One group of germ-free rats was colonized with the type 1-fimbriated Escherichia coli O6:K13:H1 and another group with the same E. coli strain together with L. plantarum 299v. One and 5 weeks after colonization, bacterial numbers were determined in the contents of the small intestine, caecum and mesenteric lymph nodes. Small intestinal sections were examined for CD8+, CD4+, CD25+ (IL-2R alpha-chain), IgA+ and MHC class II+ cells and mitogen-induced spleen cell proliferation was determined. Immunoglobulin levels and E. coli-specific antibodies were measured in serum. Rats given L. plantarum in addition to E. coli showed lower counts of E. coli in the small intestine and caecum 1 week after colonization compared with the group colonized with E. coli alone, but similar levels after 5 weeks. Rats colonized with L. plantarum + E. coli had significantly higher total serum IgA levels and marginally higher IgM and IgA antibody levels against E. coli than those colonized with E. coli alone. They also showed a significantly increased density of CD25+ cells in the lamina propria and displayed a decreased proliferative spleen cell response after stimulation with concanavalin A or E. coli 1 week after colonization. The results indicate that L. plantarum colonization competes with E. coli for intestinal colonization and can influence intestinal and systemic immunity.

Oral and intestinal microflora in 5-fluorouracil treated rats, translocation to cervical and mesenteric lymph nodes and effects of probiotic bacteria

Serious systemic infections may occur during cancer chemotherapy due to disturbances in the oropharyngeal and gastrointestinal microflora, impaired mucosal barrier functions and immunosuppression. Bacteria may spread from the gastrointestinal tract to the regional lymph nodes. The routes for bacterial spread from the oral cavity are less well known. In the present study we investigated changes in the oral and intestinal microfloras in rats given 50 mg/kg 5-fluorouracil (5-FU) i.v. for 6 days. Bacterial dissemination to the lymph nodes draining the oral cavity and the lymph nodes draining the gastrointestinal tract was examined. Effects of adding the probiotic strain Lactobacillus plantarum 299v in the drinking water to the rats were measured. 5-FU treatment caused an increase in the number of facultative and strictly anaerobic bacteria in biopsies from the oral cavity and an increase in the number of facultative anaerobes in the large intestine. The proportion of facultative gram-negative rods increased in both the oral cavity and intestine. Bacteria translocated to both the cervical and mesenteric lymph nodes in untreated animals and increased in numbers after 5-FU treatment due to an increase in the number of facultative gram-negative rods. Treatment with L. plantarum 299v improved food intake and body weight in 5-FU-treated rats. It also reduced the 5-FU-induced raise in the total numbers of facultative anaerobes in the intestine, but did not reduce translocation and did not prevent diarrhea. This study reinforces the oral cavity, along with the gastrointestinal tract, as a source for bacterial dissemination. The use of probiotic bacteria may reduce some side effects of 5-FU treatment.

Long-time persistence of superantigen-producing Staphylococcus aureus strains in the intestinal microflora of healthy infants

Staphylococcus aureus has been isolated at an increasing rate from infants' stools during the last decades, but it is not known whether this species can colonize and persist in the intestinal microflora. To investigate this, 49 Swedish infants were followed prospectively from birth until 12 months of age. S. aureus was identified in a rectal swab obtained 3 d after delivery and in quantitative cultures of fecal samples collected at 1, 2, 4, and 8 weeks and at 6 and 12 months of age. A random amplified polymorphic DNA (RAPD) method was developed to distinguish individual S. aureus strains from one another and the strains were tested for production of enterotoxins A-D and TSST-1. By 3 days of age, 16% of infants had S. aureus in their intestines, which increased to 73% by 2-6 months, whereafter it decreased slightly to 53%. At the same time S. aureus population counts in colonized infants declined from an average 10(6.8) CFU/g feces during the first months of life to 10(4.0) CFU/g feces by 12 months. Colonized infants usually harbored one or two S. aureus strains in their microflora for long periods of time. Few strains were transient passengers and the median time of persistence of S. aureus strains in the microflora was several months. Of the 75 S. aureus strains identified, 43% produced one or more toxins: 13% SEA, 7% SEB, 23% SEC, 4% SED, and 11% TSST-1. Altogether, 47% of the investigated infants were colonized by a toxin-producing S. aureus during their first year of life. Despite this they were apparently healthy and did not have more gastrointestinal problems than noncolonized infants. This report is the first to show that S. aureus may be a resident member of the normal intestinal microflora in infancy.

High turnover rate of Escherichia coli strains in the intestinal flora of infants in Pakistan

The Escherichia coli flora of infants in developed countries is dominated by one or a few strains which persist for prolonged periods of time, but no longitudinal studies have been performed in developing countries. To this end, we studied the rectal enterobacterial flora in 22 home-delivered Pakistani infants during their first 6 months of life. Three colonies were isolated and species typed on each of 11 sampling occasions. E. coli isolates were strain typed using electromorphic typing of cytoplasmic enzymes, and their O serogroups were determined. There was a very rapid turnover of enterobacterial strains in the rectal flora of individual infants. On average, 8.5 different E. coli strains were found per infant, and several biotypes of other enterobacteria. Less than 50% of the infants were colonized with E. coli from their mothers, but strains of maternal origin were four times more likely to persists in the infants' flora than other E. coli strains. Enterobacteria other than E. coli were always of non-maternal origin, and Enterobacter cloacae and Klebsiella pneumoniae biotypes recovered from contaminated feeds were later identified in the infants' rectal flora. An early colonization with klebsiella or enterobacter was significantly associated with diarrhoea during the neonatal period, although these bacteria were not likely to be the cause of the disease. The results suggest that poor hygienic conditions result in an unstable and diverse enterobacterial flora, which may influence infant health.

Spray bacteriotherapy decreases middle ear fluid in children with secretory otitis media

OBJECTIVE

Secretory otitis media (SOM) is characterised by persistent fluid in the middle ear cavity, but the cause is unknown. We investigated the clinical, bacteriological and immunological effects of treatment with probiotic bacteria on SOM.

DESIGN

In this double-blind pilot/preliminary study, 60 children with long-standing SOM (median 6 months) who were scheduled for insertion of tympanostomy tubes were randomised to nasal spray treatment with Streptococcus sanguinis, Lactobacillus rhamnosus or placebo for 10 days before surgery. Clinical evaluation was carried out after 10 days of treatment. Middle ear fluid (MEF) was collected during surgery for quantification of cytokines and detection of bacteria by culture and polymerase chain reaction (PCR). Nasopharyngeal swabs were obtained before treatment and at surgery.

RESULTS

Complete or significant clinical recovery occurred in 7/19 patients treated with S sanguinis compared to 1/17 patients in the placebo group (p<0.05). In the L rhamnosus treatment group, 3/18 patients were cured or much better (p = 0.60 compared with placebo). Spray treatment did not alter the composition of the nasopharyngeal flora or the cytokine pattern observed in the nasopharynx or MEF, except for a higher level of IL-8 found in the nasopharynx of L rhamnosus treated children.

CONCLUSIONS

This study shows that spray treatment with S sanguinis may be effective against SOM. The mechanism for the effect remains to be investigated.

P fimbriae, capsule and aerobactin characterize colonic resident Escherichia coli

Resident and transient Escherichia coli strains from the colonic microflora of 13 Swedish schoolgirls were analysed for carriage of genes encoding a range of adhesins (P, type 1 and S fimbriae, Dr haemagglutinin and three varieties of the P fimbrial papG adhesin) and other virulence traits (K1 and K5 capsule, haemolysin and aerobactin) using multiplex PCR. Forty-four percent of the resident clones carried genes for P fimbriae, K1 or K5 capsule, and aerobactin, compared with only 3% of transient clones (P < 0.0001). The P-fimbriated clones most often had the class II variety of the P-fimbrial adhesin gene papG and this adhesin was significantly associated with persistence of a strain. S fimbriae and type 1 fimbriae were equally common in resident and transient strains. The results indicate that not only P fimbriae, but also, certain capsules and the ability to produce the siderophore aerobactin might contribute to persistence of E. coli in the large intestine.

Difference between bacterial and food antigens in mucosal immunogenicity

The mucosa-associated lymphoid tissue may deviate from its systemic counterpart in being able to discriminate between microbial and nonmicrobial antigens. To study this, the systemic and mucosal antibody responses to bacterial and food antigens were followed in parallel in female rats during two pregnancies and lactation periods. Germfree rats were monocolonized with an Escherichia coli O6K13H1 strain, and their diet was switched to pellets containing large amounts of ovalbumin and beta-lactoglobulin. Antibodies against O6 lipopolysaccharide already appeared in serum and bile 1 week after colonization, and those against type 1 fimbriae appeared a few weeks later. Serum immunoglobulin G antibodies against the E. coli enzyme beta-galactosidase were found in moderate titers in all rats after 16 weeks of exposure. In contrast, few rats had detectable antibody levels against the dietary proteins ovalbumin and beta-lactoglobulin in serum or bile even after 16 weeks of exposure. In the milk, antibodies against E. coli beta-galactosidase and type 1 fimbriae reached the highest titers, while moderate titers were found against the food antigens and against O6 lipopolysaccharide. The difference in immune reactivity against bacterial versus dietary antigens was not likely due to insufficient amounts of the latter reaching lymphoid tissue, since (i) uptake studies indicated that ovalbumin was more efficiently taken up than endotoxin and (ii) the same difference in antigenicity between ovalbumin and E. coli was seen after immunization directly into Peyer's patches. We therefore suggest that a prerequisite for a strong mucosal antibody response is that the antigen be encountered by the gut-associated lymphoid tissue within microorganisms capable of stimulating antigen presentation.

Adhesins of Escherichia coli associated with extra-intestinal pathogenicity confer binding to colonic epithelial cells

Escherichia coli adhesins are virulence factors in intestinal and extra-intestinal infections, but their role in normal intestinal colonization has not been defined. We investigated the intestinal adherence of E. coli with Dr hemagglutinin, S fimbriae, CFA/I or CFA/II, using freshly isolated ileal or colonic enterocytes and cells from the human colonic cell line HT-29. E. coli with S-fimbrial adhesins (Sfa I or Sfa II), P or type 1 fimbriae, adhered in a non-polarized manner, and in similar numbers to colonic and ileal enterocytes. S fimbriae of the variety Sfa II (originating from a meningitis isolate), mediated a stronger binding than Sfa I (of uropathogenic origin). Strains expressing Dr hemagglutinin adhered preferentially to the brush borders, slightly better to colonic than ileal enterocytes. Strains expressing CFA/I or II adhered to colonic and ileal enterocytes, although brush border adherence was predominantly observed with ileal cells. Binding to HT-29 cells paralleled binding to colonic enterocytes for all adhesin specificities except CFA/I. The results suggest that Dr hemagglutinin, P-, type 1- and S-fimbrial adhesins mediate binding to both colonic and ileal enterocytes. These specificities may contribute to the establishment of E. coli in the intestinal microflora, which precedes their spread to extra-intestinal sites.

Decreased expression of mannose-specific adhesins by Escherichia coli in the colonic microflora of immunoglobulin A-deficient individuals

Most Escherichia coli isolates can express type 1 fimbriae with mannose-specific adhesins. These adhesins bind to the oligosaccharide chains of secretory immunoglobulin A (IgA). Thus, in addition to specific antibody activity, secretory IgA possesses a broad reactivity with bacteria expressing type 1 fimbriae. The absence of secretory IgA in colonic secretions, as seen in IgA deficiency, might therefore alter the ability of type 1-fimbriated E. coli to colonize the large intestines of these individuals. In the present study, 10 E. coli isolates from each of 17 IgA-deficient and 17 age-matched control individuals were assessed for the carriage of the fim gene cluster by DNA-DNA hybridization and for the expression of type 1 fimbriae by hemagglutination of guinea pig erythrocytes. The contribution of type 1-fimbria-mediated adherence to HT-29 colonic cells was also analyzed. The proportion of fim+ E. coli isolates was lower in IgA-deficient than in control individuals (74 versus 94%, P < 0.05), as was the proportion of isolates expressing type 1 fimbriae in vitro (69% versus 85%, P < 0.05). The median mannose-sensitive adherence to HT-29 cells was lower for isolates from IgA-deficient individuals than from the controls (9 versus 26 bacteria per cell, P < 0.05). Isolates expressing type 1 fimbriae showed lower adherence to HT-29 cells when they were derived from IgA-deficient individuals than when they were derived from control individuals (15 versus 27 bacteria per cell, P < 0.05). The results suggest that the interaction of type 1 fimbriae with secretory IgA contributes to the large intestinal colonization by these bacteria.

Increased levels of circulating soluble CD14 but not CD83 in infants are associated with early intestinal colonization with Staphylococcus aureus

BACKGROUND

Soluble forms of the monocyte marker CD14 and the mature dendritic cell marker CD83 are plasma proteins with immunoregulatory functions. The physiological stimulus for their production is unclear and their possible role in allergy development is unknown.

METHODS

We measured the plasma levels of soluble CD14 (sCD14) and soluble CD83 (sCD83) in 64 Swedish children in relation to intestinal bacterial colonization pattern in a prospective birth cohort. Soluble CD14 and sCD83 levels were quantified by enzyme linked immunosorbent assay in plasma obtained at birth and at 4, 18 and 36 months of age. All major aerobic and anaerobic bacteria were quantified in faecal samples obtained regularly over the first 8 weeks of life. Clinical allergy and IgE levels were evaluated at 18 months of age.

RESULTS

Soluble CD14 in plasma increased during the first 18 months of life while sCD83 peaked at 4 months of age. Children who were perinatally colonized with Staphylococcus aureus had significantly higher levels of sCD14 in plasma at 4 months of age relative to non-colonized children. The levels of sCD14 were unrelated to colonization with Escherichia coli, other enterobacteria, enterococci, clostridia, Bacteroides, bifidobacteria or lactobacilli. Further, children with food allergy by 18 months tended to have lower levels of sCD14 than healthy children. Plasma levels of sCD83 were not related to either bacterial colonization pattern or allergy development.

CONCLUSIONS

Perinatal colonization with S. aureus may trigger the occurrence of sCD14 in plasma, which may influence development of the infantile immune system and risk of allergy development.

Differential effect on cell-mediated immunity in human volunteers after intake of different lactobacilli

Probiotics are live microorganisms which have beneficial effects on the host when ingested in adequate amounts. Probiotic bacteria may stimulate immune effector functions in a strain-specific manner. In this blind placebo-controlled trial, we investigated the effects on the immune system following daily intake of six different strains of lactobacilli or the Gram-negative bacterium Pseudomonas lundensis for 2 or 5 weeks. Blood lymphocyte subsets were quantified by fluorescence activated cell sorter and the expression of activation and memory markers was determined. The bacterial strains were also examined for their capacity to adhere to human intestinal cells and to be phagocytosed by human peripheral blood mononuclear cells. Intake of Lactobacillus plantarum strain 299v increased the expression of the activation marker CD25 (P = 0·01) on CD8(+) T cells and the memory cell marker CD45RO on CD4(+) T cells (P = 0·03), whereas intake of L. paracasei tended to expand the natural killer T (NK T) cell population (P = 0·06). The phagocytic activity of granulocytes was increased following intake of L. plantarum 299v, L. plantarum HEAL, L. paracasei or L. fermentum. In contrast, ingestion of L. rhamnosus decreased the expression of CD25 and CD45RO significantly within the CD4(+) cell population. The observed immune effects after in-vivo administration of the probiotic bacteria could not be predicted by either their adherence capacity or the in-vitro-induced cytokine production. The stimulation of CD8(+) T cells and NK T cells suggests that intake of probiotic bacteria may enhance the immune defence against, e.g. viral infections or tumours.

Distinct patterns of naive, activated and memory T and B cells in blood of patients with ulcerative colitis or Crohn's disease

Both major subcategories of inflammatory bowel disease (IBD), ulcerative colitis and Crohn’s disease are characterized by infiltration of the gut wall by inflammatory effector cells and elevated biomarkers of inflammation in blood and feces. We investigated the phenotypes of circulating lymphocytes in the two types of IBD in treatment‐naive pediatric patients by analysis of blood samples by flow cytometry. Multivariate analysis was used to compare the phenotypes of the blood lymphocytes of children with ulcerative colitis (n = 17) or Crohn’s disease (n = 8) and non‐IBD control children with gastrointestinal symptoms, but no signs of gut inflammation (n = 23). The two IBD subcategories could be distinguished based on the results from the flow cytometry panel. Ulcerative colitis was characterized by activated T cells, primarily in the CD8⁺ population, as judged by increased expression of human leukocyte antigen D‐related (HLA‐DR) and the β1‐integrins [very late antigen (VLA)] and a reduced proportion of naive (CD62L⁺) T cells, compared with the non‐IBD controls. This T cell activation correlated positively with fecal and blood biomarkers of inflammation. In contrast, the patients with Crohn’s disease were characterized by a reduced proportion of B cells of the memory CD27⁺ phenotype compared to the non‐IBD controls. Both the patients with ulcerative colitis and those with Crohn’s disease showed increased percentages of CD23⁺ B cells, which we demonstrate here as being naive B cells. The results support the notion that the two major forms of IBD may partially have different pathogenic mechanisms.

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.