Gut microbiota and development of atopic eczema in 3 European birth cohorts

Mucosal control of the intestinal microbial community

Although the knowledge of the effects of bacterial colonization on the immune system is rapidly expanding, surprisingly little is known about the immunological mechanisms that shape the intestinal microbial community. Specifically, the complexity of the intestinal microbiota and what constitutes a "healthy" microbial composition has only recently been addressed, facilitated by large-scale metagenomic screens. Containment of such a vast number of different microbes requires tight regulation at the mucosal surface. While beneficial relationships must not be compromised, invading pathogenic bacteria must be dealt with in order to maintain homeostasis. In this review, we will address the latest insights into the role of the mucosal immune system in the control of the microbiota.

The 'hygiene hypothesis' for autoimmune and allergic diseases: an update

According to the 'hygiene hypothesis', the decreasing incidence of infections in western countries and more recently in developing countries is at the origin of the increasing incidence of both autoimmune and allergic diseases. The hygiene hypothesis is based upon epidemiological data, particularly migration studies, showing that subjects migrating from a low-incidence to a high-incidence country acquire the immune disorders with a high incidence at the first generation. However, these data and others showing a correlation between high disease incidence and high socio-economic level do not prove a causal link between infections and immune disorders. Proof of principle of the hygiene hypothesis is brought by animal models and to a lesser degree by intervention trials in humans. Underlying mechanisms are multiple and complex. They include decreased consumption of homeostatic factors and immunoregulation, involving various regulatory T cell subsets and Toll-like receptor stimulation. These mechanisms could originate, to some extent, from changes in microbiota caused by changes in lifestyle, particularly in inflammatory bowel diseases. Taken together, these data open new therapeutic perspectives in the prevention of autoimmune and allergic diseases.

99th Dahlem conference on infection, inflammation and chronic inflammatory disorders: controversial aspects of the 'hygiene hypothesis'

The 'hygiene hypothesis' proposes that the epidemic of allergic and autoimmune diseases is due to changes in the interactions between humans and the microbes of their ecosystem. This theory apparently does not explain (i) why allergic asthma is rising in 'unhygienic' American inner cities; (ii) why allergic diseases are less prevalent among migrants' children living in European big cities; (iii) why infections with airborne viruses do not 'protect' from allergic sensitization; (iv) why the inverse association between some infections (e.g. hepatitis A virus) and allergic diseases has been reproduced in some populations, but not in others; and (v) why probiotics are not effective in the prevention and therapy of allergic diseases. These challenging questions are useful starting points to improve our understanding of the hypothesis, and to identify among the infectious agents those really responsible for a protective influence against atopic and autoimmune diseases.

Guidance for substantiating the evidence for beneficial effects of probiotics: prevention and management of allergic diseases by probiotics

Allergy is a hypersensitivity reaction mediated by specific antibody-mediated or cell-mediated immunologic mechanisms and clinically manifested as atopic eczema, allergic rhinoconjunctivitis, or asthma. During the recent decades there has been an increase in allergy prevalence, which is attributed to changes in environmental factors. The so-called "hygiene hypothesis" suggests that a lack of exposure to microbial stimulus early in childhood is a major factor involved in this trend. This provides a rationale for using probiotics to modify the gut microbiota and thereby shaping the immune response of the host, especially in infancy. Most success has been obtained in primary prevention of atopic eczema. A limited number of studies also provided evidence for a beneficial effect of different probiotics in the management of allergic diseases (atopic eczema, allergic rhinitis). However, choice of probiotic strains as well as timing of the intervention are important variables. The exact in vivo mechanism of probiotics in shaping the immune response still needs to be determined. Future studies should use uniform criteria for diagnosis and symptom scoring of atopic diseases and may identify the genes predisposing to allergic disease. There is encouraging evidence that specific probiotics can become valuable tools in the prevention and management of allergic diseases.

Probiotics and prebiotics in atopic dermatitis: review of the theoretical background and clinical evidence

The prevalence of atopic dermatitis (AD) has risen over the past decades, especially in western societies. According to the revised hygiene hypothesis this increase is caused by a changed intestinal colonization pattern during infancy, which has an impact on the immune system. Manipulating the intestinal microflora with pro-, pre- or synbiotics is an innovative way to prevent or treat AD. This review provides an overview of the theoretical basis for using probiotics and prebiotics in AD and presents the current evidence from randomized controlled trials (RCTs) regarding prevention and treatment of AD and food allergy in children with pro-, pre- and synbiotics. Seven RCTs on prevention and 12 RCTs on treatment were found by searching the Pubmed, Embase and Cochrane databases. Results of these trials are conflicting. In conclusion, at this moment there is not enough evidence to support the use of pro-, pre- or synbiotics for prevention or treatment of AD in children in clinical practice.

The importance of the development of the intestinal microbiota in infancy

PURPOSE OF REVIEW

The development of the intestinal microbiota occurs primarily during infancy, and a distortion could potentially contribute to a wide range of diseases. This review summarizes the current understanding of the intestinal microbiota in infants. The potential consequences of different colonization patterns on child health and possible preventive interventions are discussed.

RECENT FINDINGS

Recent studies and the use of culture-independent techniques have shown that Bifidobacterium is only a minor component of the infant gut microbiota. These techniques have also introduced the concept of a core microbiome in which metabolic function is more important than the presence of a particular bacterial species. A less diverse gut microbiota with high counts of Bacteroides, Clostridium, Enterobacteriaceae and Staphylococcus early in life has been associated with an increased risk for atopic disease. Changes in infant gut colonization were also found in relation to childhood obesity. Probiotics have no proven preventive effect on the development of asthma and an unconfirmed effect on atopic dermatitis. A prebiotic trial could show a preventive effect on the development of both atopic diseases.

SUMMARY

Molecular techniques have improved our understanding of the infant gut ecosystem. The available probiotics for prevention of atopic disease are disappointing, and the results with prebiotics need further confirmation. New studies on the relation between gut microbiota and disease should consider asthma and atopic dermatitis separately. Future trials should focus on high-risk groups, determine their long-term effect and also investigate the effect on Bacteroides and Clostridium.

The role of probiotics in allergic diseases

Allergic disorders are very common in the pediatric age group. While the exact etiology is unclear, evidence is mounting to incriminate environmental factors and an aberrant gut microbiota with a shift of the Th1/Th2 balance towards a Th2 response. Probiotics have been shown to modulate the immune system back to a Th1 response. Several in vitro studies suggest a role for probiotics in treating allergic disorders. Human trials demonstrate a limited benefit for the use of probiotics in atopic dermatitis in a preventive as well as a therapeutic capacity. Data supporting their use in allergic rhinitis are less robust. Currently, there is no role for probiotic therapy in the treatment of bronchial asthma. Future studies will be critical in determining the exact role of probiotics in allergic disorders.

Superantigenic Staphylococcus aureus stimulates production of interleukin-17 from memory but not naive T cells

T-helper 17 (Th17) cells are characterized by their production of interleukin-17 (IL-17) and have a role in the protection against infections and in certain inflammatory diseases. Humans who lack Th17 cells are more susceptible to Staphylococcus aureus infections compared to individuals having Th17 cells. S. aureus is part of the commensal skin microflora and also colonize the infant gut. To investigate whether UV-killed S. aureus would be more capable of inducing IL-17 than other commensal bacteria, we stimulated mononuclear cells from adults, infants, and newborns with various gram-positive and gram-negative commensal bacteria. IL-17 was produced from adult memory Th17 cells after stimulation with superantigen-producing S. aureus but not nonsuperantigenic S. aureus or other common commensal gut bacteria. Cells from newborns were poor IL-17 producers after stimulation with S. aureus, whereas in some cases IL-17 was secreted from cells isolated from infants at the age of 4 and 18 months. These results suggest that superantigenic S. aureus are particularly efficient in stimulating IL-17 production and that the cytokine is produced from memory T cells.

Impact of neonatal antibiotic treatment on the biodiversity of the murine intestinal Lactobacillus community

In this study, we investigated the impact of neonatal amoxicillin treatment on the development of the murine intestinal Lactobacillus community. Suckling BALB/c mice received a daily intragastric gavage of amoxicillin or saline from postnatal day 7 (PND 7) to PND 20. Just after the treatment (PND 21) and 5 weeks later (PND 56), the colon digesta samples were analyzed by Lactobacillus-specific quantitative real-time PCR analysis and PCR-denaturing gradient gel electrophoresis (DGGE) technique. Real-time PCR results showed that the levels of lactobacilli in the treatment group were similar to those in the control at PND 56. However, in DGGE analysis the number of DGGE bands and Shannon index were decreased significantly in comparison with control (P < 0.05). The dominant Lactobacillus strain in the murine colon changed from L. johnsonii to L. murinus. These results demonstrated that neonatal amoxicillin treatment led to a significant impact on the biodiversity of the murine intestinal Lactobacillus community within a long-time period.

Influence of early gut microbiota on the maturation of childhood mucosal and systemic immune responses

INTRODUCTION

Among sensitized infants, those with high, as compared with low levels, of salivary secretory IgA (SIgA) are less likely to develop allergic symptoms. Also, early colonization with certain gut microbiota, e.g. Lactobacilli and Bifidobacterium species, might be associated with less allergy development. Although animal and in vitro studies emphasize the role of the commensal gut microbiota in the development of the immune system, the influence of the gut microbiota on immune development in infants is unclear.

OBJECTIVE

To assess whether early colonization with certain gut microbiota species associates with mucosal and systemic immune responses i.e. salivary SIgA and the spontaneous Toll-like receptor (TLR) 2 and TLR4 mRNA expression and lipopolysaccharide (LPS)-induced cytokine/chemokine responses in peripheral blood mononuclear cells (PBMCs).

METHODS

Fecal samples were collected at 1 week, 1 month and 2 months after birth from 64 Swedish infants, followed prospectively up to 5 years of age. Bacterial DNA was analysed with real-time PCR using primers binding to Clostridium difficile, four species of bifidobacteria, two lactobacilli groups and Bacteroides fragilis. Saliva was collected at age 6 and 12 months and at 2 and 5 years and SIgA was measured with ELISA. The PBMCs, collected 12 months after birth, were analysed for TLR2 and TLR4 mRNA expression with real-time PCR. Further, the PBMCs were stimulated with LPS, and cytokine/chemokine responses were measured with Luminex.

RESULTS

The number of Bifidobacterium species in the early fecal samples correlated significantly with the total levels of salivary SIgA at 6 months. Early colonization with Bifidobacterium species, lactobacilli groups or C. difficile did not influence TLR2 and TLR4 expression in PBMCs. However, PBMCs from infants colonized early with high amounts of Bacteroides fragilis expressed lower levels of TLR4 mRNA spontaneously. Furthermore, LPS-induced production of inflammatory cytokines and chemokines, e.g. IL-6 and CCL4 (MIP-1 beta), was inversely correlated to the relative amounts of Bacteroides fragilis in the early fecal samples.

CONCLUSION

Bifidobacterial diversity may enhance the maturation of the mucosal SIgA system and early intense colonization with Bacteroides fragilis might down-regulate LPS responsiveness in infancy.

Probiotic lactobacilli in breast milk and infant stool in relation to oral intake during the first year of life

OBJECTIVES

This is to identify factors affecting the prevalence of Lactobacillus reuteri in maternal faeces and breast milk and infant faeces after oral supplementation with L reuteri and to assess the influence on microbial ecology, particularly Clostridium difficile and Bifidobacterium colonization.

MATERIALS AND METHODS

In this double-blind trial, 232 mothers with a family history of atopic disease were randomized to a daily intake of either L reuteri American-type culture collection (ATCC) 55730 (1 x 10 colony-forming units [CFU]) or placebo for the last 4 weeks of pregnancy. Their babies then continued with the same study product daily from birth until 12 months of age. Bacterial counts and prevalence were assessed in maternal breast milk and faeces and infant faeces, using conventional cultivation methods.

RESULTS

The prevalence of L reuteri was higher during the first year of life in the stool samples from infants in the active as compared with the placebo-treated group. The highest prevalence was recorded at 5 to 6 days of age (82% in the treated vs 20% in the placebo group, P < 0.001). Lactobacillus reuteri was isolated from 12% and 2%, respectively, in the colostrum samples (P < 0.05). Breast-feeding seemed to reduce faecal L reuteri counts, although antibiotics did not influence the levels of L reuteri. The administration of L reuteri did not affect bifidobacteria or C difficile colonization.

CONCLUSION

Lactobacillus reuteri may be detected in breast milk after oral supplementation to the mother and in almost all infants after oral supplementation during the first year of life, as well as occasionally in many untreated infants.

The long-term health effects of neonatal microbial flora

PURPOSE OF REVIEW

Colonization of the newborn intestine is a complex process evolving over the first year of life. It is partly responsible for guiding immunologic development within the infant. Given the sharp escalation in immunologic diseases such as allergy and inflammatory bowel disease (IBD), this microbial-host interaction has become the focus of intense interest. DNA-based detection techniques have allowed increased identification of specific microbes involved in this symbiosis.

RECENT FINDINGS

Epidemiologic studies have demonstrated a link between allergic diseases and alterations in the colonizing flora of infants. Concurrently, other work has demonstrated that interactions between gut flora and the intestinal epithelium seem to be central to the pathogenesis of IBD. In both allergy and IBD, certain bacteria seem to provide beneficial, protective effects via immune modulation.

SUMMARY

There is a complex interaction between the bacteria within the developing gut and the immune system of the host. Colonization of the neonatal gut represents a critical window in this process. It appears clear that disruption within this flora has long-term health consequences as diverse as eczema, allergic rhinitis, and IBD. Guided establishment of specific species within the flora may reduce the incidence of these diseases.

Probiotics and immunology: separating the wheat from the chaff

Probiotics are live bacteria exhibiting health-promoting activities. Recent research has demonstrated that probiotics can prevent pathogen colonization of the gut and reduce the incidence or relieve the symptoms of various diseases caused by dysregulated immune responses. Probiotics seem to function by influencing both intestinal epithelial cells and immune cells of the gut, but the details of these effects are still being unraveled. Therefore, probiotics, through their effects on the host immune system, might ameliorate diseases triggered by disordered immune responses. Caveats remain and, because the beneficial effects of probiotics can vary between strains, the selection of the most suitable ones will be crucial for their use in the prevention or treatment of specific diseases.

Faecal short chain fatty acid pattern and allergy in early childhood

AIM

To investigate whether functional changes of the gut flora over time were related to sensitization and allergic symptoms at four years of age.

METHODS

The levels of short chain fatty acids (SCFAs) in faecal samples at one (n = 139) and four (n = 53) years of age were related to the development of positive skin prick tests (SPT) and allergic symptoms during the first four years of life.

RESULTS

Faecal acetic (p < 0.01) and propionic (p < 0.01) acids decreased from one to four years of age, while valeric acid (p < 0.001) increased. Low levels of i-butyric (p = 0.01), i-valeric (p = 0.03) and valeric acids (p = 0.02) at one year were associated with questionnaire-reported symptoms of food allergy at four years. Positive SPTs and allergic symptoms at four years were associated with low faecal levels of i-butyric, i-valeric and valeric acids. At one year of age, infants with, as compared to without older siblings had higher median levels of valeric acid.

CONCLUSION

A slow functional maturation of the gut microflora, as measured by faecal levels of SCFAs is associated with allergy both at one and four years. The findings lend further support to an association between allergy and the development of microbial diversity.

Probiotics and immunity

Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host, including the gastrointestinal tract. While this beneficial effect was originally thought to stem from improvements in the intestinal microbial balance, there is now substantial evidence that probiotics can also provide benefits by modulating immune functions. In animal models, probiotic supplementation is able to provide protection from spontaneous and chemically induced colitis by downregulating inflammatory cytokines or inducing regulatory mechanisms in a strain-specific manner. In animal models of allergen sensitization and murine models of asthma and allergic rhinitis, orally administered probiotics can strain-dependently decrease allergen-specific IgE production, in part by modulating systemic cytokine production. Certain probiotics have been shown to decrease airway hyperresponsiveness and inflammation by inducing regulatory mechanisms. Promising results have been obtained with probiotics in the treatment of human inflammatory diseases of the intestine and in the prevention and treatment of atopic eczema in neonates and infants. However, the findings are too variable to allow firm conclusions as to the effectiveness of specific probiotics in these conditions.

Altered early infant gut microbiota in children developing allergy up to 5 years of age

BACKGROUND

Early colonization with bifidobacteria and lactobacilli is postulated to protect children from allergy, while Clostridium (C.) difficile colonization might be associated with allergic disease. Previous studies of infant gut microbiota in relation to subsequent allergy development have mostly employed culture-dependent techniques, studied genera of bacteria and the follow-up period was limited to 2 years.

OBJECTIVE

To relate gut microbiota in early infancy, notably bifidobacteria and lactobacilli at species level, to allergy development during the first 5 years of life and study if environmental factors influence the early infant gut microbiota.

METHODS

Fecal samples were collected at 1 week, 1 month and 2 months after birth from 47 Swedish infants, followed prospectively to 5 years of age. Bacterial DNA was analysed with real-time PCR and related to allergy development, family size as well as endotoxin and Fel d 1 levels in house dust samples. Primers binding to C. difficile, four species of bifidobacteria, two lactobacilli groups and Bacteroides fragilis were used. Children regarded as allergic manifested allergic symptoms and were skin prick test positive during their first 5 years while non-allergic children were neither.

RESULTS

Children who developed allergy were significantly less often colonized with lactobacilli group I (Lactobacillus (L.) rhamnosus, L. casei, L. paracasei), Bifidobacterium adolescentis and C. difficile during their first 2 months. Infants colonized with several Bifidobacterium species had been exposed to higher amounts of endotoxin and grew up in larger families than infants harbouring few species.

CONCLUSION

A more diverse gut microbiota early in life might prevent allergy development and may be related to the previously suggested inverse relationship between allergy, family size and endotoxin exposure.

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.

Is there an increased frequency of food allergy in children delivered by caesarean section compared to those delivered vaginally?

AIM

Allergic diseases are increasing. At the same time an increasing number of children are delivered by caesarean section. These children do not get the same contact with their mother's gut flora as babies delivered vaginally. Theoretically, lack of exposure to maternal vaginal and perineal bacteria might change the gut flora, with secondary changes in the immune system. The aim of this study was to investigate whether children delivered by caesarean section were more prone to develop food allergy.

METHODS

Six hundred and nine children were included at birth. At 2-year follow-up, 512 children participated, 171 delivered by caesarean section, 341 born vaginally. The children reported to have symptoms consistent with possible food allergy, were examined at the outpatient clinic. The diagnosis was based on the history, skin prick test (SPT), specific IgE, elimination/challenge test and double blind placebo controlled challenge.

RESULTS

Thirty-five (6.8%) children were diagnosed with adverse reactions to food, 27 with non-IgE-mediated and eight with IgE-mediated allergy. There was no over representation of children born by caesarean section.

CONCLUSION

In this study there seems to be no increased risk for food allergy in the first 2 years of life in children delivered by caesarean section.

Probiotics prevent IgE-associated allergy until age 5 years in cesarean-delivered children but not in the total cohort

BACKGROUND

Less microbial exposure in early childhood is associated with more allergic disease later. Allergic children have a different fecal microflora, with less lactobacilli and bifidobacteria. Beneficial effects regarding the development of allergy have been suggested to come through probiotic supplementation.

OBJECTIVE

We sought to study the effect of probiotic and prebiotic supplementation in preventing allergies.

METHODS

In a double-blinded, placebo-controlled study we randomized 1223 mothers with infants at high risk for allergy to receive a probiotic mixture (2 lactobacilli, bifidobacteria, and propionibacteria) or placebo during the last month of pregnancy and their infants to receive it from birth until age 6 months. Infants also received a prebiotic galacto-oligosaccharide or placebo. At 5 years, we evaluated the cumulative incidence of allergic diseases (eczema, food allergy, allergic rhinitis, and asthma) and IgE sensitization.

RESULTS

Of the 1018 intent-to-treat infants, 891 (88%) attended the 5-year visit. Frequencies of allergic and IgE-associated allergic disease and sensitization in the probiotic and placebo groups were similar: 52.6% versus 54.9% and 29.5% versus 26.6%, respectively, and 41.3% in both. No significant difference appeared in frequencies of eczema (39.3% vs 43.3%), atopic eczema (24.0% vs 25.1%), allergic rhinitis (20.7% vs 19.1%), or asthma (13.0% vs 14.1%) between groups. However, less IgE-associated allergic disease occurred in cesarean-delivered children receiving probiotics (24.3% vs 40.5%; odds ratio, 0.47; 95% CI, 0.23% to 0.96%; P = .035).

CONCLUSIONS

No allergy-preventive effect that extended to age 5 years was achieved with perinatal supplementation of probiotic bacteria to high-risk mothers and children. It conferred protection only to cesarean-delivered children.

[What's new in clinical dermatology]

This selection reviews several topics in the news: - in internal medicine, the cardiovascular and pulmonary risk factors in progressive systemic sclerosis (circulating lupus anticoagulant, smoking, NT-pro BNP marker); the relations between lupus erythematous and polymorphic light eruption, or Jessner-Kanof syndrome; the diagnostic score of autoinflammatory syndromes; and the dysmetabolism syndrome of psoriasis; - in infectious diseases, the return of epidemic typhus; the emergence of TIBOLA rickettsiosis; the development of methicillin-resistant Staphylococcus aureus strains in both the nosocomial and community settings; and finally news on herpes group viral infections.

Diversity of the gut microbiota and eczema in early life

BACKGROUND

A modest number of prospective studies of the composition of the intestinal microbiota and eczema in early life have yielded conflicting results.

OBJECTIVE

To examine the relationship between the bacterial diversity of the gut and the development of eczema in early life by methods other than stool culture.

METHODS

Fecal samples were collected from 21 infants at 1 and 4 months of life. Nine infants were diagnosed with eczema by the age of 6 months (cases) and 12 infants were not (controls). After conducting denaturating gradient gel electrophoresis (DGGE) of stool samples, we compared the microbial diversity of cases and controls using the number of electrophoretic bands and the Shannon index of diversity (H') as indicators.

RESULTS

Control subjects had significantly greater fecal microbial diversity than children with eczema at ages 1 (mean H' for controls = 0.75 vs. 0.53 for cases, P = 0.01) and 4 months (mean H' for controls = 0.92 vs. 0.59 for cases, P = 0.02). The increase in diversity from 1 to 4 months of age was significant in controls (P = 0.04) but not in children who developed eczema by 6 months of age (P = 0.32).

CONCLUSION

Our findings suggest that reduced microbial diversity is associated with the development of eczema in early life.

Soluble bacterial constituents down-regulate secretion of IL-12 in response to intact Gram-positive bacteria

Intact Gram-positive bacteria induce production of large amounts of IL-12 from freshly isolated human monocytes. Here the bacterial structures and signalling pathways involved were studied and compared with those leading to IL-6 production, and to IL-12 production in response to LPS after IFN-gamma pre-treatment. Intact bifidobacteria induced massive production of IL-12 (1 ng/ml) and IL-6 (>30 ng/ml) from human PBMC, whereas fragmented bifidobacteria induced IL-6, but no IL-12. IL-12 production induced by intact bifidobacteria was inhibited by pre-treatment with bifidobacterial sonicate, peptidoglycan, muramyl dipeptide, lipoteichoic acid, the soluble TLR2 agonist Pam(3)Cys-SK(4), or anti-TLR2 antibodies. Blocking of phagocytosis by cytochalasin, inhibition of the JNK or NF-kappaB pathways or treatment with Wortmannin also reduced the IL-12 response to intact Gram-positive bacteria. LPS induced moderate levels of IL-12 (0.31 ng/ml), but only from IFN-gamma pre-treated PBMC. This IL-12 production was enhanced by Wortmannin and unaffected by blocking the JNK pathway. Thus, intact Gram-positive bacteria trigger monocyte production of large amounts of IL-12 via a distinct pathway that is turned off by fragmented Gram-positive bacteria. This may be a physiological feedback, since such fragments may signal that further activation of the phagocyte via the IL-12/IFN-gamma loop is unnecessary.

Postnatal development of intestinal microflora as influenced by infant nutrition

The postnatal period of a new human being is characterized, from the microbiological point of view, by the formation of a new ecosystem: the microflora of the human gut. In adulthood a number of barriers exert a potent selective action on bacteria arriving from the mouth, but in the very first stage of our life, these barriers are kept at a very low level, temporarily allowing penetration into the gut of bacteria that are not really believed to be "gut related." Moreover, type of delivery (natural vs. cesarean) and feeding (breast vs. bottle feeding) play dramatic roles in determining the microflora composition. In the last decade a number of articles have reported results on neonates' microflora obtained by means of culture-independent analysis. Data obtained by means of these techniques are in agreement with those produced by selective media, but they also provide some new insights about the presence of anaerobic bacteria. The focus of this article is to update knowledge on infants' microflora during the first 6 mo of life.

New perspectives on mechanisms underlying chronic allergic inflammation and asthma in 2007

This review summarizes selected articles appearing from January to December 2007 in the Journal of Allergy and Clinical Immunology. Articles were chosen that related to advances in mechanisms of chronic allergic inflammation and asthma, including those describing gene association studies, mast cells, IgE, eosinophils, cytokines, the inception of allergy, airway remodeling, preclinical therapeutic targets, and virally induced asthma.

Intestinal carriage of Staphylococcus aureus: how does its frequency compare with that of nasal carriage and what is its clinical impact?

The bacterial species Staphylococcus aureus, including its methicillin-resistant variant (MRSA), finds its primary ecological niche in the human nose, but is also able to colonize the intestines and the perineal region. Intestinal carriage has not been widely investigated despite its potential clinical impact. This review summarizes literature on the topic and sketches the current state of affairs from a microbiological and infectious diseases' perspective. Major findings are that the average reported detection rate of intestinal carriage in healthy individuals and patients is 20% for S. aureus and 9% for MRSA, which is approximately half of that for nasal carriage. Nasal carriage seems to predispose to intestinal carriage, but sole intestinal carriage occurs relatively frequently and is observed in 1 out of 3 intestinal carriers, which provides a rationale to include intestinal screening for surveillance or in outbreak settings. Colonization of the intestinal tract with S. aureus at a young age occurs at a high frequency and may affect the host's immune system. The frequency of intestinal carriage is generally underestimated and may significantly contribute to bacterial dissemination and subsequent risk of infections. Whether intestinal rather than nasal S. aureus carriage is a primary predictor for infections is still ill-defined.

Birth by cesarean section, allergic rhinitis, and allergic sensitization among children with a parental history of atopy

BACKGROUND

Cesarean delivery can alter neonatal immune responses and increase the risk of atopy. Studies of the relation between cesarean delivery and allergic diseases in children not selected on the basis of a family history of atopy have yielded inconsistent findings.

OBJECTIVE

We sought to examine the relation between birth by cesarean delivery and atopy and allergic diseases in children at risk for atopy.

METHODS

We examined the relation between mode of delivery and the development of atopy and allergic diseases among 432 children with a parental history of atopy followed from birth to age 9 years. Asthma was defined as physician-diagnosed asthma and wheeze in the previous year, and allergic rhinitis was defined as physician-diagnosed allergic rhinitis and naso-ocular symptoms apart from colds in the previous year. Atopy was considered present at school age if there was 1 or more positive skin test response or specific IgE to common allergens. Stepwise logistic regression was used to study the relation between cesarean delivery and the outcomes of interest.

RESULTS

After adjustment for other covariates, children born by cesarean section had 2-fold higher odds of atopy than those born by vaginal delivery (odds ratio, 2.1; 95% CI, 1.1-3.9). In multivariate analyses birth by cesarean section was significantly associated with increased odds of allergic rhinitis (odds ratio, 1.8; 95% CI, 1.0-3.1) but not with asthma.

CONCLUSIONS

Our findings suggest that cesarean delivery is associated with allergic rhinitis and atopy among children with a parental history of asthma or allergies. This could be explained by lack of contact with the maternal vaginal/fecal flora or reduced/absent labor during cesarean delivery.

Differential transcriptional response of Bifidobacterium longum to human milk, formula milk, and galactooligosaccharide

In order to gain insight into the effects of human breast milk on the development of the intestinal bifidobacteria and associated health effects, the transcriptome of Bifidobacterium longum LMG 13197 grown in breast milk and formula milk containing galactooligosaccharides (GOS) and long-chain fructooligosaccharides was compared to that obtained in a semisynthetic medium with glucose. Total RNA was isolated from exponentially growing cells and hybridized to a clone library-based microarray. Inserts of clones with significant hybridization signals were sequenced and identified. The B. longum transcriptomes obtained during growth on human and formula milk were more similar to each other than to that obtained from growth in semisynthetic medium with glucose. Remarkably, there were only a few genes implicated in carbohydrate metabolism that were similarly upregulated during growth in both human and formula milk although oligosaccharides were added to the formula. Common highly upregulated genes notably included putative genes for cell surface type 2 glycoprotein-binding fimbriae that are implicated in attachment and colonization in the intestine. Genes involved in carbohydrate metabolism formed the dominant group specifically upregulated in breast milk and included putative genes for N-acetylglucosamine degradation and for metabolism of mucin and human milk oligosaccharides via the galactose/lacto-N-biose gene cluster. This supports the notion that the bifidogenic effect of human milk is to a great extent based on its oligosaccharides. The transcriptional effect of semisynthetic medium containing GOS, which, like human milk, contains a large amount of lactose and galactose, on the B. longum transcriptome was also studied and revealed substantial similarity with carbohydrate-utilization genes upregulated during growth in human milk. This knowledge provides leads to optimizing formula milk to better simulate the observed bifidogenic effects of human breast milk.

Asthma and obesity: common early-life influences in the inception of disease

The respective prevalences of both asthma and obesity have seen a significant rise in the past few decades. Although the association between these 2 conditions has been found in many studies from different areas around the world, the exact mechanisms for how this association arises remains unresolved. Because both asthma and obesity appear to have their beginnings in early childhood, common exposures that predispose individuals to both these conditions may explain how they are associated. These exposures include common genetic predictors, prenatal exposure to specific nutrients and overall maternal nutrition, patterns of colonization of the neonatal and infant gut, birth weight and infant weight gain, sedentary behaviors, and levels of adipokines in early life.

Infections presenting for clinical care in early life and later risk of hay fever in two UK birth cohorts

BACKGROUND

The 'hygiene hypothesis' proposes that infections in infancy protect against hay fever (HF). We investigated infections during infancy in relation to HF, including rarer ones not previously researched in this context, while examining the role of potential confounding variables.

METHODS

From birth cohorts derived within the General Practice Research Database (GPRD) and Doctors Independent Network (DIN) database of computerized patient records from UK general practice, we selected 3549 case-control pairs, matched for practice, age, sex and control follow-up to case diagnosis. Conditional logistic regressions were fitted for each of 30 infections; behavioural problems (BP) acted as a control condition unrelated to HF. Odds ratios (OR), adjusted for consultation frequency were pooled across the databases using fixed effect models. We also adjusted for sibship size in GPRD and a socioeconomic marker in DIN.

RESULTS

Upper respiratory tract infections, diarrhoea and vomiting and acute otitis media in infancy were each related with a moderately increased risk of HF in both databases, as were BP. These associations were lost on adjustment for consultation frequency. Only bronchiolitis was significantly associated with a reduced pooled risk of HF after adjustment for consultations (OR = 0.8). Adjustment for sibship size in GPRD and a socioeconomic marker in DIN had little impact on the OR.

CONCLUSIONS

Of 30 infectious illnesses investigated, none had strong or consistent associations with HF after adjustment for consultation frequency. Except for bronchiolitis, possibly a chance finding, none of the clinically apparent infections considered appear to have an important role in allergy prevention.

Primary prevention of allergy: avoiding risk or providing protection?

Primary prevention strategies of allergy so far have been aimed to fight allergy causes, by avoiding risk factors and inhibiting their mechanisms of action. The results of trials testing food or airborne allergen avoidance as a prevention strategy were, however, rather disappointing. A reverse approach for primary prevention of allergies aims to facilitate exposure to protecting factors which promote the induction of immunologic tolerance against innocuous antigens. These factors are associated with farming environment and a 'traditional lifestyle', but identification of these factors is quite difficult. Major candidates include food-borne microbes, helminths or their components, which are able to stimulate mucosal immunity, particularly in the gut. Similarly, new preventive and therapeutic strategies are being tested to induce specific food-allergen oral tolerance through the ingestion of progressively increasing doses of the offending food. This shifting of allergy prevention research from avoidance to tolerance induction will hopefully allow us to reverse the epidemic trend of allergy diseases.

Reduced diversity in the early fecal microbiota of infants with atopic eczema

BACKGROUND

It might be that early intestinal colonization by bacteria in westernized infants fails to give rise to sufficient immune stimulation to support maturation of regulatory immune mechanisms.

OBJECTIVE

The purpose of the present study was to characterize the very early infantile microbiota by using a culture-independent approach and to relate the colonization pattern to development of atopic eczema in the first 18 months of life.

METHODS

Fecal samples were collected from 35 infants at 1 week of age. Twenty infants were healthy, and 15 infants were given diagnoses of atopic eczema at the age of 18 months. The fecal microbiota of the infants was compared by means of terminal restriction fragment length polymorphism (T-RFLP) and temporal temperature gradient gel electrophoresis (TTGE) analysis of amplified 16S rRNA genes.

RESULTS

By means of T-RFLP analysis, the median number of peaks, Shannon-Wiener index, and Simpson index of diversity were significantly less for infants with atopic eczema than for infants remaining healthy in the whole group and for the Swedish infants when AluI was used for digestion. The same was found when TTGE patterns were compared. In addition, TTGE analysis showed significantly less bands and lower diversity indices for the British atopic infants compared with those of the control subjects.

CONCLUSION

There is a reduced diversity in the early fecal microbiota of infants with atopic eczema during the first 18 months of life.