Influence of the intestinal flora on the development of immune reactions in infants

Insights from 100 Years of Research with Probiotic E. Coli

A century ago, Alfred Nissle discovered that intentional intake of particular strains of Escherichia coli could treat patients suffering from infectious diseases. Since then, one of these strains became the most frequently used probiotic E. coli in research and was applied to a variety of human conditions. Here, properties of that E. coli Nissle 1917 strain are compared with other commercially available E. coli probiotic strains, with emphasis on their human applications. A literature search formed the basis of a summary of research findings reported for the probiotics Mutaflor, Symbioflor 2, and Colinfant. The closest relatives of the strains in these products are presented, and their genetic content, including the presence of virulence, genes is discussed. A similarity to pathogenic strains causing urinary tract infections is noticeable. Historic trends in research of probiotics treatment for particular human conditions are identified. The future of probiotic E. coli may lay in what Alfred Nissle originally discovered: to treat gastrointestinal infections, which nowadays are often caused by antibiotic-resistant pathogens.

Review of sn-2 palmitate oil implications for infant health

Human milk provides the optimal balanced nutrition for the growing infant in the first months after birth. The human mammary gland has evolved with unusual pathways, resulting in a specific positioning of fatty acids at the outer sn-1 and sn-3, and center sn-2 of the triacylglyceride, which is different from the triglycerides in other human tissues and plasma. The development of structured triglycerides enables mimicking the composition as well as structure of human milk fat in infant formulas. Studies conducted two decades ago, together with very recent studies, have provided increasing evidence that this unusual positioning of 16:0 in human milk triglycerides has a significant role for infant health in different directions, such as fat and calcium absorption, bone health, intestinal flora and infant comfort. This review aims to unravel the relevance of human milk triglyceride sn-2 16:0 for intestinal health and inflammatory pathways and for other post-absorption effects.

Effect of high β-palmitate content in infant formula on the intestinal microbiota of term infants

OBJECTIVES

Palmitic acid (PA) constitutes 17% to 25% of the human milk fatty acids, and ~70% is esterified in the sn-2 position of triglycerides (β-palmitate). In the sn-2 position, PA is not hydrolyzed and thus is efficiently absorbed. The PA in palm oils, commonly used in infant formulas, is esterified in the sn-1 and sn-3 positions. In these positions, PA is hydrolyzed and forms poorly absorbed calcium complexes. The present study assessed whether high β-palmitate in infant formulas affects the intestinal flora.

METHODS

Thirty-six term infants were enrolled: 14 breast-fed (BF group) and 22 formula-fed infants who were randomly assigned to receive formula containing high β-palmitate (HBP group, n=14), or low β-palmitate (LBP group, n=8), where 44% and 14% of the PA was β-palmitate, respectively. The total amount of PA in the formulas was 19% and 22% in the LBP and HBP groups, respectively. Neither formula contained pre- or probiotics. Stool samples were collected at enrollment and at 6 weeks for the quantification of bacteria.

RESULTS

At 6 weeks, the HBP and BF groups had higher Lactobacillus and bifidobacteria counts than the LBP group (P<0.01). The Lactobacillus counts at 6 weeks were not significantly different between the HBP and BF groups. Lactobacillus counts were 1.2×10¹⁰, 1.2×10¹¹, and 5.6×10¹⁰ CFU/g for LBP, HBP, and BF groups, respectively. Bifidobacteria counts were 5.1×10⁹, 1.2×10¹¹, and 3.9×10¹⁰ CFU/g for LBP, HBP, and BF groups, respectively.

CONCLUSIONS

HBP formula beneficially affected infant gut microbiota by increasing the Lactobacillus and bifidobacteria counts in fecal stools.

Characterization of a restriction modification system from the commensal Escherichia coli strain A0 34/86 (O83:K24:H31)

Background

Type I restriction-modification (R-M) systems are the most complex restriction enzymes discovered to date. Recent years have witnessed a renaissance of interest in R-M enzymes Type I. The massive ongoing sequencing programmes leading to discovery of, so far, more than 1 000 putative enzymes in a broad range of microorganisms including pathogenic bacteria, revealed that these enzymes are widely represented in nature. The aim of this study was characterisation of a putative R-M system EcoA0ORF42P identified in the commensal Escherichia coli A0 34/86 (O83: K24: H31) strain, which is efficiently used at Czech paediatric clinics for prophylaxis and treatment of nosocomial infections and diarrhoea of preterm and newborn infants.

Results

We have characterised a restriction-modification system EcoA0ORF42P of the commensal Escherichia coli strain A0 34/86 (O83: K24: H31). This system, designated as EcoAO83I, is a new functional member of the Type IB family, whose specificity differs from those of known Type IB enzymes, as was demonstrated by an immunological cross-reactivity and a complementation assay. Using the plasmid transformation method and the RM search computer program, we identified the DNA recognition sequence of the EcoAO83I as GGA(8N)ATGC. In consistence with the amino acids alignment data, the 3' TRD component of the recognition sequence is identical to the sequence recognized by the EcoEI enzyme. The A-T (modified adenine) distance is identical to that in the EcoAI and EcoEI recognition sites, which also indicates that this system is a Type IB member. Interestingly, the recognition sequence we determined here is identical to the previously reported prototype sequence for Eco377I and its isoschizomers.

Conclusion

Putative restriction-modification system EcoA0ORF42P in the commensal Escherichia coli strain A0 34/86 (O83: K24: H31) was found to be a member of the Type IB family and was designated as EcoAO83I. Combination of the classical biochemical and bacterial genetics approaches with comparative genomics might contribute effectively to further classification of many other putative Type-I enzymes, especially in clinical samples.

Specific regions of genome plasticity and genetic diversity of the commensal Escherichia coli A0 34/86

Escherichia coli A0 34/86 (O83:K24:H31) is a commensal strain that has been used for prophylactic and therapeutic colonization of the intestine of newborn infants. To identify traits specific for E. coli A0 34/86, we used a minimal tiling set of 148 BAC clones of A0 34/86 genomic DNA, to construct restriction-digested BAC arrays. Hybridization with genomic DNA from four E. coli strains (CFT073; O157:H7; K12 and Nissle 1917) allowed selection of two BAC clones that were sequenced to identify A0 34/86-specific regions. Genes for the yersiniabactin siderophore system, several proteins homologous to Salmonella enterica serovar Typhimurium vitamin B12 synthesis proteins, as well as genes necessary for the degradation of propanediol, the pix fimbriae determinant and genes coding for a putative phosphoglycerate transport system present also on pathogenicity island V of E. coli strain 536 were all identified in E. coli A0 34/86. This comparative analysis underlines the important genome heterogeneity between E. coli strains.

HlyA knock out yields a saferEscherichia coliA0 34/86 variant with unaffected colonization capacity in piglets

Escherichia coli A0 34/86 (O83:K24:H31) has been successfully used for prophylactic and therapeutic intestinal colonization of premature and newborn infants, with the aim of preventing nosocomial infections. Although E. coli A0 34/86 was described as a nonpathogenic commensal, partial sequencing revealed that its genome harbours gene clusters highly homologous to virulence determinants of different types of E. coli, including closely linked genes of the alpha-haemolysin operon (hlyCABD) and for the cytotoxic necrotizing factor (cnf1). A haemolysin-deficient mutant (Delta hlyA) of E. coli A0 34/86 was generated and its colonization capacity was determined. The results show that a single dose of the A0 34/86 wild-type or Delta hlyA strains resulted in efficient intestinal colonization of newborn conventional piglets, and that this was still considerable after several weeks. No difference was observed between the wild-type and the mutant strains, showing that haemolysin expression does not contribute to intestinal colonization capacity of E. coli A0 34/86. Safety experiments revealed that survival of colostrum-deprived gnotobiotic newborn piglets was substantially higher upon colonization by the nonhaemolytic strain than following inoculation by its wild-type ancestor. We suggest that the E. coli A0 34/86 Delta hlyA mutant may represent a safer prophylactic and/or immunomodulatory tool with unaffected colonization capacity.

Characterization of the flexible genome complement of the commensal Escherichia coli strain A0 34/86 (O83 : K24 : H31)

Colonization by the commensal Escherichia coli strain A0 34/86 (O83 : K24 : H31) has proved to be safe and efficient in the prophylaxis and treatment of nosocomial infections and diarrhoea of preterm and newborn infants in Czech paediatric clinics over the past three decades. In searching for traits contributing to this beneficial effect related to the gut colonization capacity of the strain, the authors have analysed its genome by DNA-DNA hybridization to E. coli K-12 (MG1655) genomic DNA arrays and to 'Pathoarrays', as well as by multiplex PCR, bacterial artificial chromosome (BAC) library cloning and shotgun sequencing. Four hundred and ten E. coli K-12 ORFs were absent from A0 34/86, while 72 out of 456 genes associated with pathogenicity islands of E. coli and Shigella were also detected in E. coli A0 34/86. Furthermore, extraintestinal pathogenic E. coli-related genes involved in iron uptake and adhesion were detected by multiplex PCR, and genes encoding the HlyA and cytotoxic necrotizing factor toxins, together with 21 genes of the uropathogenic E. coli 536 pathogenicity island II, were identified by analysis of 2304 shotgun and 1344 BAC clone sequences of A0 34/86 DNA. Multiple sequence comparisons identified 31 kb of DNA specific for E. coli A0 34/86; some of the genes carried by this DNA may prove to be implicated in the colonization capacity of the strain, enabling it to outcompete pathogens. Among 100 examined BAC clones roughly covering the A0 34/86 genome, one reproducibly conferred on the laboratory strain DH10B an enhanced capacity to persist in the intestine of newborn piglets. Sequencing revealed that this BAC clone carried gene clusters encoding gluconate and mannonate metabolism, adhesion (fim), invasion (ibe) and restriction/modification functions. Hence, the genome of this clinically safe and highly efficient colonizer strain appears to harbour many 'virulence-associated' genes. These results highlight the thin line between bacterial 'virulence' and 'fitness' or 'colonization' factors, and question the definition of enterobacterial virulence factors.

Specific proliferative and antibody responses of premature infants to intestinal colonization with nonpathogenic probiotic E. coli strain Nissle 1917

The aim of this study was to analyze the influence of oral administration of E. coli Nissle 1917 on the systemic humoral and cellular immunity in premature infants. Thirty-four premature infants were colonized with E. coli Nissle 1917 in a randomized, placebo-controlled blinded clinical trial. Stool samples of infants were analyzed repeatedly for the presence of the administered strain. The proliferative response to bacterial antigens of E. coli origin was measured in whole blood of 34 colonized infants and 27 noncolonized controls. E. coli colonization induced a significant increase in the proliferation of blood cells cultivated with bacterial components of E. coli Nissle 1917 and another E. coli strain in colonized infants as compared with noncolonized controls. Significantly higher amounts of specific anti-E. coli Nissle 1917 antibodies (Ab) of immunoglobulin (Ig)A isotype and nonspecific polyclonal IgM were found in the blood of colonized infants compared to noncolonized placebo controls. We concluded that the oral application of E. coli Nissle 1917 after birth significantly stimulates specific humoral and cellular responses and simultaneously induces nonspecific natural immunity.

Intestinal colonization and antibody response

Rapid bacterial colonization of the gastrointestinal tract takes place immediately after birth. Only a few of the Escherichia coli strains colonizing the gut of healthy full-term neonates expressed MS pili. On the other hand, most E. coli strains isolated carried MR pili resembling the P-fimbriae which are a known virulence factor for pyelonephritogenic E. coli. The presence of serum antibodies against pili and K antigens of E. coli after vaccination did not influence the capacity of E. coli to colonize and persist in the intestine of experimental animals.

Adhesion of piliated Escherichia coli strains to phagocytes: differences between bacteria with mannose-sensitive pili and those with mannose-resistant pili

Escherichia coli with mannose-resistant (MR) pili, in contrast to those with mannose-sensitive (MS) pili, did not adhere to rat peritoneal macrophages and human polymorphonuclear granulocytes, as measured by use of radioactive bacteria and by the chemiluminescence response induced by the cell contact. With some MS-piliated E. coli strains, unpiliated bacteria, obtained by growth at a pilus-restrictive temperature, did show MS adherence to phagocytes, presumably by virtue of bacterial cell wall adhesins which, like MS pili, recognize alpha-mannose-containing structures of the phagocyte membrane. Possible roles of MR pili, MS pili, and MS cell wall adhesins in the unspecific cellular host defense are discussed.

Heteroimmunization to the capsular polysaccharide of Haemophilus influenzae type b induced by enteric cross-reacting bacteria

Cross-reacting Escherichia coli strains Easter and 89 and Bacillus pumilis fed to newborn rabbits and E. coli fed to adult rhesus monkeys did not exert untoward reactions. The E. coli regularly colonized the newborns' intestinal tract from 1 to 7 weeks. High doses of E. coli were necessary to colonize adult primates. Colonization occurred in fewer newborn rabbits and lasted only 1 to 3 weeks with B. pumilis. Colonized newborn rabbits and adult rhesus had an active Haemophilus influenzae type b (HITB) immune response. In the rabbit, colonization resulted in accelerated induction of immunoglobulin (Ig) M-. IgA-, and IgG-producing cells in the spleen, mesenteric lymph nodes, and Peyer's patches after HITB challenge. E. coli-fed and control newborn primates were naturally colonized with nasopharyngeal and enteric cross-reacting bacteria and both groups rapidly developed HITB antibodies in the absence of the homologous organisms. Human newborn stool cultures, taken at the time of discharge from the nursery, showed a 0.9% carriage rate for cross-reacting E. coli. These "carrier" infants acquired HITB antibodies more rapidly than their age-matched "noncarrier" controls.

Induction of Haemophilus influenzae type b capsular antibody in neonatal rabbits by gastrointestinal colonization with cross-reacting Escherichia coli

In two separate experiments, newborn rabbits were fed a live suspension of either of two Escherichia coli strains which possess a "K" antigen cross-reactive with the capsular polysaccharide of Haemophilus influenzae type b. Both feedings were harmless and resulted in fecal excretion of the fed E. coli in most animals as well as active immunization of fed animals toward H. influenzae type b. Feeding non-enteropathogenic, cross-reacting E coli to newborns may be a method for inducing active immunity toward H. influenzae type b diseases by accelerating the acquisition of "natural" immunity.

Monoclonal immunoglobulins in congenital toxoplasmosis

Monoclonal immunoglobulins in serum and cerebrospinal fluid (CSF) were found in newborns with congenital toxoplasmosis. The M-components were of IgG-class and of both κ and λ type. The monoclonal proteins were found in the serum of newborns but not in the serum of their mothers. The monoclonal immunoglobulins were therefore selectively transferred or synthesized by the newborn. There was a local production or selective local accumulation of immunoglobulins in the cerebrospinal fluid. The M-components disappeared and the IgM level in serum and cerebrospinal fluid decreased after therapy. IgA was found to be elevated between 2–4 months of age. CRP was elevated in the first weeks after birth but afterwards returned to normal. The Dye test localized antibody activity to the site of the M-components in the electrophoresis of both serum and cerebrospinal fluid. The Dye test antibodies of mothers' sera also showed restricted heterogeneity with about the same electrophoretic localization as in the children's sera. Rheumatoid factors were found in serum and CSF of newborns with congenital toxoplasmosis, but not in serum of their mothers.