Eradication of the commensal intestinal microflora by oral antimicrobials interferes with the host response to lipopolysaccharide

Virus Infection Is an Instigator of Intestinal Dysbiosis Leading to Type 1 Diabetes

In addition to genetic predisposition, environmental determinants contribute to a complex etiology leading to onset of type 1 diabetes (T1D). Multiple studies have established the gut as an important site for immune modulation that can directly impact development of autoreactive cell populations against pancreatic self-antigens. Significant efforts have been made to unravel how changes in the microbiome function as a contributor to autoimmune responses and can serve as a biomarker for diabetes development. Large-scale longitudinal studies reveal that common environmental exposures precede diabetes pathology. Virus infections, particularly those associated with the gut, have been prominently identified as risk factors for T1D development. Evidence suggests recent-onset T1D patients experience pre-existing subclinical enteropathy and dysbiosis leading up to development of diabetes. The start of these dysbiotic events coincide with detection of virus infections. Thus viral infection may be a contributing driver for microbiome dysbiosis and disruption of intestinal homeostasis prior to T1D onset. Ultimately, understanding the cross-talk between viral infection, the microbiome, and the immune system is key for the development of preventative measures against T1D.

Evaluating the Causal Role of Gut Microbiota in Type 1 Diabetes and Its Possible Pathogenic Mechanisms

Type 1 diabetes (T1D) is a multifactorial autoimmune disease mediated by genetic, epigenetic, and environmental factors. In recent years, the emergence of high-throughput sequencing has allowed us to investigate the role of gut microbiota in the development of T1D. Significant changes in the composition of gut microbiome, also termed dysbiosis, have been found in subjects with clinical or preclinical T1D. However, whether the dysbiosis is a cause or an effect of the disease remains unclear. Currently, increasing evidence has supported a causal link between intestine microflora and T1D development. The current review will focus on recent research regarding the associations between intestine microbiome and T1D progression with an intention to evaluate the causality. We will also discuss the possible mechanisms by which imbalanced gut microbiota leads to the development of T1D.

Antibiotics, gut microbiota, environment in early life and type 1 diabetes

The gut microbiota interact with innate immune cells and play an important role in shaping the immune system. Many factors may influence the composition of the microbiota such as mode of birth, diet, infections and medication including antibiotics. In diseases with a multifactorial etiology, like type 1 diabetes, manipulation and alterations of the microbiota in animal models have been shown to influence the incidence and onset of disease. The microbiota are an important part of the internal environment and understanding how these bacteria interact with the innate immune cells to generate immune tolerance may open up opportunities for development of new therapeutic strategies. In this review, we discuss recent findings in relation to the microbiota, particularly in the context of type 1 diabetes.

Intestinal colonization among very low birth weight infants in first week of life

OBJECTIVE

To study intestinal colonization patterns in very low birth weight infants in the first week of life in a neonatal intensive care unit.

METHODS

Meconium/stool specimens were obtained on days 1, 3, 5 and 7 from 38 very low-birth-weight infants in a level III neonatal intensive care unit.

RESULTS

On day 1, 45% had sterile guts, and by day 3, all infants were colonized. E. coli, K. pneumoniae and Enterococcus fecalis were predominant organisms. Lactobacilli was found in one isolate and Bifidobacteria was not detected during the study period. There was an association between formula feeding and E. coli colonization.

CONCLUSION

Very low birth weight infants admitted in neonatal intensive care units have abnormal intestinal colonization patterns.

Short-term effect of antibiotics on human gut microbiota

From birth onwards, the human gut microbiota rapidly increases in diversity and reaches an adult-like stage at three years of age. After this age, the composition may fluctuate in response to external factors such as antibiotics. Previous studies have shown that resilience is not complete months after cessation of the antibiotic intake. However, little is known about the short-term effects of antibiotic intake on the gut microbial community. Here we examined the load and composition of the fecal microbiota immediately after treatment in 21 patients, who received broad-spectrum antibiotics such as fluoroquinolones and β-lactams. A fecal sample was collected from all participants before treatment and one week after for microbial load and community composition analyses by quantitative PCR and pyrosequencing of the 16S rRNA gene, respectively. Fluoroquinolones and β-lactams significantly decreased microbial diversity by 25% and reduced the core phylogenetic microbiota from 29 to 12 taxa. However, at the phylum level, these antibiotics increased the Bacteroidetes/Firmicutes ratio (p = 0.0007, FDR = 0.002). At the species level, our findings unexpectedly revealed that both antibiotic types increased the proportion of several unknown taxa belonging to the Bacteroides genus, a Gram-negative group of bacteria (p = 0.0003, FDR<0.016). Furthermore, the average microbial load was affected by the treatment. Indeed, the β-lactams increased it significantly by two-fold (p = 0.04). The maintenance of or possible increase detected in microbial load and the selection of Gram-negative over Gram-positive bacteria breaks the idea generally held about the effect of broad-spectrum antibiotics on gut microbiota.

Strategies to minimize antibiotic resistance

Antibiotic resistance can be reduced by using antibiotics prudently based on guidelines of antimicrobial stewardship programs (ASPs) and various data such as pharmacokinetic (PK) and pharmacodynamic (PD) properties of antibiotics, diagnostic testing, antimicrobial susceptibility testing (AST), clinical response, and effects on the microbiota, as well as by new antibiotic developments. The controlled use of antibiotics in food animals is another cornerstone among efforts to reduce antibiotic resistance. All major resistance-control strategies recommend education for patients, children (e.g., through schools and day care), the public, and relevant healthcare professionals (e.g., primary-care physicians, pharmacists, and medical students) regarding unique features of bacterial infections and antibiotics, prudent antibiotic prescribing as a positive construct, and personal hygiene (e.g., handwashing). The problem of antibiotic resistance can be minimized only by concerted efforts of all members of society for ensuring the continued efficiency of antibiotics.

Stimulation of macrophages by immunobiotic Lactobacillus strains: influence beyond the intestinal tract

Lactobacillus rhamnosus CRL1505 (Lr1505), L. rhamnosus CRL1506 (Lr1506) and L. casei CRL431 (Lc431) are able to stimulate intestinal immunity, but only Lr1505 and Lc431 are able to stimulate immunity in the respiratory tract. With the aim of advancing the understanding of the immunological mechanisms involved in stimulation of distant mucosal sites, this study evaluated the effects of orally administered probiotics on the functions of alveolar and peritoneal macrophages. Compared to a control group, these three lactobacilli were able to significantly increase phagocytic and microbicidal activities of peritoneal macrophages. After intraperitoneal challenge with pathogenic Candida albicans, mice treated with immunobiotics had significantly lower pathogen counts in infected organs. Moreover, lactobacilli-treated mice had a stronger immune response against C. albicans. On the other hand, only Lc1505 and Lc431 were able to improve activity of and cytokine production by alveolar macrophages. Only in these two groups was there better resistance to respiratory challenge with C. albicans, which correlated with improved respiratory immune response. The results of this study suggest that consumption of some probiotic strains could be useful for improving resistance to infections in sites distant from the gut by increasing the activity of macrophages at those sites.

Orally administered Lactobacillus rhamnosus modulates the respiratory immune response triggered by the viral pathogen-associated molecular pattern poly(I:C)

Background

Some studies have shown that probiotics, including Lactobacillus rhamnosus CRL1505, had the potential to beneficially modulate the outcome of certain bacterial and viral respiratory infections. However, these studies did not determine the mechanism(s) by which probiotics contribute to host defense against respiratory viruses.

Results

In this work we demonstrated that orally administered Lactobacillus rhamnosus CRL1505 (Lr1505) was able to increase the levels of IFN-γ, IL-10 and IL-6 in the respiratory tract and the number of lung CD3⁺CD4⁺IFN-γ⁺ T cells. To mimic the pro-inflammatory and physiopathological consecuences of RNA viral infections in the lung, we used an experimental model of lung inflammation based on the administration of the artificial viral pathogen-associated molecular pattern poly(I:C). Nasal administration of poly(I:C) to mice induced a marked impairment of lung function that was accompanied by the production of pro-inflammatory mediators and inflammatory cell recruitment into the airways. The preventive administration of Lr1505 reduced lung injuries and the production of TNF-α, IL-6, IL-8 and MCP-1 in the respiratory tract after the challenge with poly(I:C). Moreover, Lr1505 induced a significant increase in lung and serum IL-10. We also observed that Lr1505 was able to increase respiratory IFN-γ levels and the number of lung CD3⁺CD4⁺IFN-γ⁺ T cells after poly(I:C) challenge. Moreover, higher numbers of both CD103⁺ and CD11b^high dendritic cells and increased expression of MHC-II, IL-12 and IFN-γ in these cell populations were found in lungs of Lr1505-treated mice. Therefore, Lr1505 treatment would beneficially regulate the balance between pro-inflammatory mediators and IL-10, allowing an effective inflammatory response against infection and avoiding tissue damage.

Conclusions

Results showed that Lr1505 would induce a mobilization of cells from intestine and changes in cytokine profile that would be able to beneficially modulate the respiratory mucosal immunity. Although deeper studies are needed using challenges with respiratory viruses, the results in this study suggest that Lr1505, a potent inducer of antiviral cytokines, may be useful as a prophylactic agent to control respiratory virus infection.

Chemoenzymatic synthesis of an isoprenoid phosphate tool for the analysis of complex bacterial oligosaccharide biosynthesis

Undecaprenyl Pyrophosphate Synthase (UPPS) is a key enzyme that catalyzes the production of bactoprenols, which act as membrane anchors for the assembly of complex bacterial oligosaccharides. One of the major hurdles in understanding the assembly of oligosaccharide assembly is a lack of chemical tools to study this process, since bactoprenols and the resulting isoprenoid-linked oligosaccharides lack handles or chromophores for use in pathway analysis. Here we describe the isolation of a new UPPS from the symbiotic microorganism Bacteroides fragilis, a key species in the human microbiome. The protein was purified to homogeneity and utilized to accept a chromophore containing farnesyl diphosphate analogue as a substrate. The analogue was utilized by the enzyme and resulted in a bactoprenyl diphosphate product with an easy to monitor tag associated with it. Furthermore, the diphosphate is shown to be readily converted to monophosphate using a common molecular biology reagent. This monophosphate product allowed for the investigation of complex oligosaccharide biosynthesis, and was used to probe the activity of glycosyltransferases involved in the well characterized Campylobacter jejuni N-linked protein glycosylation. Novel reagents similar to this will provide key tools for the study of uncharacterized oligosaccharide assemblies, and open the possibility for the development of rapid screening methodology for these biosynthetic systems.

Control of antiviral immunity by pattern recognition and the microbiome

Human skin and mucosal surfaces are in constant contact with resident and invasive microbes. Recognition of microbial products by receptors of the innate immune system triggers rapid innate defense and transduces signals necessary for initiating and maintaining the adaptive immune responses. Microbial sensing by innate pattern-recognition receptors is not restricted to pathogens. Rather, proper development, function, and maintenance of innate and adaptive immunity rely on continuous recognition of products derived from the microorganisms indigenous to the internal and external surfaces of mammalian host. Tonic immune activation by the resident microbiota governs host susceptibility to intestinal and extra-intestinal infections, including those caused by viruses. This review highlights recent developments in innate viral recognition leading to adaptive immunity, and discusses potential links between viruses, microbiota, and the host immune system. Furthermore, we discuss the possible roles of microbiome in chronic viral infection and pathogenesis of autoimmune disease and speculate on the benefit for probiotic therapies against such diseases.

Shifting the balance: antibiotic effects on host-microbiota mutualism

Antibiotics have been used effectively as a means to treat bacterial infections in humans and animals for over half a century. However, through their use, lasting alterations are being made to a mutualistic relationship that has taken millennia to evolve: the relationship between the host and its microbiota. Host-microbiota interactions are dynamic; therefore, changes in the microbiota as a consequence of antibiotic treatment can result in the dysregulation of host immune homeostasis and an increased susceptibility to disease. A better understanding of both the changes in the microbiota as a result of antibiotic treatment and the consequential changes in host immune homeostasis is imperative, so that these effects can be mitigated.

Dominant role of the MyD88-dependent signaling pathway in mediating early endotoxin-induced murine ileus

TLR4 ligation by pathogen-associated molecular patterns, such as Gram-negative bacteria-derived LPS, triggers a nonhematopoietic cell-mediated ileus during early endotoxemia. Our objective was to investigate the quantitative contributions of the two downstream signaling pathways of TLR4, namely the adapter proteins myeloid differentiation primary response gene 88 (MyD88) and Toll-IL-1-resistance (TIR) domain-containing adaptor-inducing IFN-beta (TRIF). Six hours after intraperitoneal injection of highly purified LPS (UP-LPS, 5 mg/kg), in vivo gastrointestinal transit and intestinal muscularis gene transcripts of inflammatory mediators chemokine (C-X-C motif) ligand 10, synonymous IP-10 (CXCL10), granulomonocyte colony stimulating factor (GM-CSF, synonymous CSF-2), IL-1beta, IL-6, IL-10, and inducible NO synthase (iNOS) were assessed in mice with transgenic loss-of-function for MyD88 or TRIF. LPS-induced MyD88 and TRIF mRNA upregulation was quantified within the intestinal muscularis of TLR4-competent and TLR4-mutant mice, and MyD88 mRNA levels were additionally measured in TLR4 bone marrow chimeras. MyD88 deficiency completely protected mice from early endotoxin-induced ileus, while TRIF deficiency partially ameliorated ileus severity. LPS induction of the primary downstream signaling element MyD88 was TLR4 dependent and was derived in equal amounts from both the hematopoietic and the nonhematopoietic cells. Conversely, no induction of TRIF mRNA was detectable. Significant gene induction of all inflammatory mediators was dependent on intracellular signal transduction by MyD88, while the TRIF MyD88-independent pathway predominantly regulated the molecular levels of CXCL10. In summary, MyD88 and TRIF are nonredundant signaling pathways in early endotoxin-induced rodent ileus, but MyD88 is the essential adaptor molecule for transduction of early TLR4-induced ileus and inflammatory signaling. The dependency of ileus on individual adaptor protein pathways is also reflected in the manifestation of specific molecular inflammatory events within the intestinal muscularis externa.