Broad specificity of monoclonal IgA (TEPC15-IgA) for enteric bacteria via phosphorylcholine-mediated interaction.

Immunoglobulin A (IgA) is notable for its broad specificity toward multiple bacteria. Phosphorylcholine (PC) plays a role in the infection of pathogenic bacteria carrying PC and in the induction of IgA responses in the host immune system. The commercially available mouse monoclonal IgA, TEPC15-IgA, is a distinctive antibody with specificity for PC, warranting further exploration of its response to PC-bearing enteric bacteria. In this study, using 17 different enteric bacteria, including 3 aerobic and 14 anerobic bacteria that could be cultured in vitro, we confirmed that TEPC15-IgA recognizes 4 bacterial species: Lactobacillus taiwanensis, Limosilactobacillus frumenti, Streptococcus infantis, and Escherichia coli, although reactivity varied. Interestingly, TEPC15-IgA did not react with four of six Lactobacillus species used. Moreover, distinct target molecules associated with PC in L. taiwanensis and L. frumenti were evident, differing in molecular weight. These findings suggest that the natural generation of PC-specific IgA could prevent PC-mediated infections and potentially facilitate the formation of a microflora rich in indigenous bacteria with PC, particularly in the gastrointestinal tract.

Psychological stress impairs IL22-driven protective gut mucosal immunity against colonising pathobionts.

Crohn's disease is an inflammatory disease of the gastrointestinal tract characterized by an aberrant response to microbial and environmental triggers. This includes an altered microbiome dominated by Enterobacteriaceae and in particular adherent-invasive E. coli (AIEC). Clinical evidence implicates periods of psychological stress in Crohn's disease exacerbation, and disturbances in the gut microbiome might contribute to the pathogenic mechanism. Here we show that stress-exposed mice develop ileal dysbiosis, dominated by the expansion of Enterobacteriaceae. In an AIEC colonisation model, stress-induced glucocorticoids promote apoptosis of CD45+CD90+ cells that normally produce IL-22, a cytokine that is essential for the maintenance of ileal mucosal barrier integrity. Blockade of glucocorticoid signaling or administration of recombinant IL-22 restores mucosal immunity, prevents ileal dysbiosis, and blocks AIEC expansion. We conclude that psychological stress impairs IL-22-driven protective immunity in the gut, which creates a favorable niche for the expansion of pathobionts that have been implicated in Crohn's disease. Importantly, this work also shows that immunomodulation can counteract the negative effects of psychological stress on gut immunity and hence disease-associated dysbiosis.

Intraspecific variation in immune gene expression and heritable symbiont density.

Host genetic variation plays an important role in the structure and function of heritable microbial communities. Recent studies have shown that insects use immune mechanisms to regulate heritable symbionts. Here we test the hypothesis that variation in symbiont density among hosts is linked to intraspecific differences in the immune response to harboring symbionts. We show that pea aphids (Acyrthosiphon pisum) harboring the bacterial endosymbiont Regiella insecticola (but not all other species of symbionts) downregulate expression of key immune genes. We then functionally link immune expression with symbiont density using RNAi. The pea aphid species complex is comprised of multiple reproductively-isolated host plant-adapted populations. These 'biotypes' have distinct patterns of symbiont infections: for example, aphids from the Trifolium biotype are strongly associated with Regiella. Using RNAseq, we compare patterns of gene expression in response to Regiella in aphid genotypes from multiple biotypes, and we show that Trifolium aphids experience no downregulation of immune gene expression while hosting Regiella and harbor symbionts at lower densities. Using F1 hybrids between two biotypes, we find that symbiont density and immune gene expression are both intermediate in hybrids. We propose that in this system, Regiella symbionts are suppressing aphid immune mechanisms to increase their density, but that some hosts have adapted to prevent immune suppression in order to control symbiont numbers. This work therefore suggests that antagonistic coevolution can play a role in host-microbe interactions even when symbionts are transmitted vertically and provide a clear benefit to their hosts. The specific immune mechanisms that we find are downregulated in the presence of Regiella have been previously shown to combat pathogens in aphids, and thus this work also highlights the immune system's complex dual role in interacting with both beneficial and harmful microbes.

Immune response during the onset of coliform mastitis in dairy cows vaccinated with STARTVAC®.

The immune response during the onset of coliform mastitis in vaccinated cows was investigated by measuring lactoferrin (LF), interleukin-8 (IL-8), and interleukin-1ß (IL-1ß) concentrations and somatic cell counts in 28 milk samples at the onset of acute coliform mastitis (ACM) and 73 milk samples at the onset of peracute coliform mastitis (PCM). Vaccinated ACM, unvaccinated ACM, and vaccinated PCM showed significantly higher values for LF and IL-1ß levels than unvaccinated PCM (p < .01). The IL-8 concentration was lower in vaccinated PCM than in unvaccinated PCM (p < .05). There was no significant difference in somatic cell counts for each parameter. There were no significant differences in the parameters between vaccinated and unvaccinated ACM cows, or vaccinated ACM and PCM cows. From the above results, it is suggested that mastitis vaccination improved the early immune response, particularly at the onset of PCM, and played a large role in host defense against the initial infection.

Lactococcus lactis and Resveratrol Decrease Body Weight and Increase Benefic Gastrointestinal Microbiota in Mice.

BACKGROUND: The microbiome is now known for its important role in whole-body homeostasis. A dysbiosis of the normal microbiota is correlated with metabolic disorders. In this sense, the search for compounds able to modulate the microbiome is needed. Resveratrol, a natural compound found in grapes seems to be a promising candidate. OBJECTIVE: In this study, our motivation was to evaluate the effects of the association between Resveratrol and Lactococcus lactis, a probiotic, on the composition of the gastrointestinal microbiota and body weight of mice. METHODS: Twenty female mice were divided into 4 groups: (1) standard diet, (2) standard diet plus Lactococcus lactis, (3) standard diet plus resveratrol, and (4) standard diet plus Lactococcus lactis and resveratrol. At the end of the treatment period, samples of blood, mucus, stomach, and small and large intestines were collected for analysis. Total levels of Immunoglobulin A and Immunoglobulin E, Lac+ and Lac- bacteria and Lactobacillus were measured. RESULTS: The main results indicate that the association between resveratrol and probiotics was able to decrease mice body weight, as compared to the other groups, in addition to decrease the number of Lac- bacteria and increasing the number of Lac+ bacteria. The levels of secretory IgA were also decreased, compared to the animals treated with only probiotics or resveratrol. CONCLUSION: We observed potential synergism between Resveratrol and Lactococcus lactis mainly in modulating the stomach and intestinal microbiota.

Broadly reactive human CD4+ T cells against Enterobacteriaceae are found in the naïve repertoire and are clonally expanded in the memory repertoire.

Enterobacteriaceae are a large family of Gram-negative bacteria that includes both commensals and opportunistic pathogens. The latter can cause severe nosocomial infections, with outbreaks of multi-antibiotics resistant strains, thus being a major public health threat. In this study, we report that Enterobacteriaceae-reactive memory Th cells were highly enriched in a CCR6+ CXCR3+ Th1*/17 cell subset and produced IFN-γ, IL-17A, and IL-22. This T cell subset was severely reduced in septic patients with K. pneumoniae bloodstream infection who also selectively lacked circulating K. pneumonie-reactive T cells. By combining heterologous antigenic stimulation, single cell cloning and TCR Vß sequencing, we demonstrate that a large fraction of memory Th cell clones was broadly cross-reactive to several Enterobacteriaceae species. These cross-reactive Th cell clones were expanded in vivo and a large fraction of them recognized the conserved outer membrane protein A antigen. Interestingly, Enterobacteriaceae broadly cross-reactive T cells were also prominent among in vitro primed naïve T cells. Collectively, these data point to the existence of immunodominant T cell epitopes shared among different Enterobacteriaceae species and targeted by cross-reactive T cells that are readily found in the pre-immune repertoire and are clonally expanded in the memory repertoire.

The Network of Colonic Host Defense Peptides as an Innate Immune Defense Against Enteropathogenic Bacteria.

Host defense peptides, abundantly secreted by colonic epithelial cells and leukocytes, are proposed to be critical components of an innate immune response in the colon against enteropathogenic bacteria, including Shigella spp., Salmonella spp., Clostridium difficile, and attaching and effacing Escherichia coli and Citrobacter rodentium. These short cationic peptides are bactericidal against both Gram-positive and -negative enteric pathogens, but may also exert killing effects on intestinal luminal microbiota. Simultaneously, these peptides modulate numerous cellular responses crucial for gut defenses, including leukocyte chemotaxis and migration, wound healing, cytokine production, cell proliferation, and pathogen sensing. This review discusses recent advances in our understanding of expression, mechanisms of action and microbicidal and immunomodulatory functions of major colonic host defense peptides, namely cathelicidins, ß-defensins, and members of the Regenerating islet-derived protein III (RegIII) and Resistin-like molecule (RELM) families. In a theoretical framework where these peptides work synergistically, aspects of pathogenesis of infectious colitis reviewed herein uncover roles of host defense peptides aimed to promote epithelial defenses and prevent pathogen colonization, mediated through a combination of direct antimicrobial function and fine-tuning of host immune response and inflammation. This interactive host defense peptide network may decode how the intestinal immune system functions to quickly clear infections, restore homeostasis and avoid damaging inflammation associated with pathogen persistence during infectious colitis. This information is of interest in development of host defense peptides (either alone or in combination with reduced doses of antibiotics) as antimicrobial and immunomodulatory therapeutics for controlling infectious colitis.

Dust mite-derived Enterobacterial fimbriae H protein enforces the allergen specific immunotherapy in asthma mice.

BACKGROUND: The mite alimentary canal contains plenty of microbiota. It is accepted that some of the microbial products function as adjuvants to speed up immune responses. OBJECTIVES: We identified five bacterial proteins from dust mite, and Enterobacterial fimbriae H (FimH) was one of them. This study aims to test a hypothesis that the FimH protein enforces immunotherapy in asthmatic mice. METHODS: Asthmatic mice were treated by allergen specific immunotherapy (ASIT) with rDer f1/f2 or rDer f1/f2 plus FimH. Changes in inflammatory cell infiltration, airway hyperreactivity, frequency of Tregs, splenic CD4+IFN-γ+ cells, and serum levels of TGF-ß, IL-10, IL-13 and IL-17A of asthmatic mice were checked. RESULTS: ASIT with rDer f1/f2 plus FimH reduced inflammatory cell infiltration, airway hyperreactivity (AHR), and levels of IgE and IgG1 compared to ASIT with rDer f1/f2 alone, but the levels of IgG2a increased. Asthmatic mice that underwent ASIT with rDer f1/f2 plus FimH showed increased frequency of Tregs, splenic CD4+IFN-γ+ cells, serum levels of TGF-ß and IL-10; and deceased splenic CD4+IL-4+ cells, and serum levels of IL-13 and IL-17A. In vitro study showed FimH triggered IL-10 expression in a concentration dependent manner and facilitated the differentiation of Tregs. CONCLUSION: Used as an adjuvant, FimH enforces the effect of ASIT in asthmatic mice via augmenting Tregs.

Colonic microbiota is associated with inflammation and host epigenomic alterations in inflammatory bowel disease.

Studies of inflammatory bowel disease (IBD) have been inconclusive in relating microbiota with distribution of inflammation. We report microbiota, host transcriptomics, epigenomics and genetics from matched inflamed and non-inflamed colonic mucosa [50 Crohn's disease (CD); 80 ulcerative colitis (UC); 31 controls]. Changes in community-wide and within-patient microbiota are linked with inflammation, but we find no evidence for a distinct microbial diagnostic signature, probably due to heterogeneous host-microbe interactions, and show only marginal microbiota associations with habitual diet. Epithelial DNA methylation improves disease classification and is associated with both inflammation and microbiota composition. Microbiota sub-groups are driven by dominant Enterbacteriaceae and Bacteroides species, representative strains of which are pro-inflammatory in vitro, are also associated with immune-related epigenetic markers. In conclusion, inflamed and non-inflamed colonic segments in both CD and UC differ in microbiota composition and epigenetic profiles.

Vying for the control of inflammasomes: The cytosolic frontier of enteric bacterial pathogen-host interactions.

Enteric pathogen-host interactions occur at multiple interfaces, including the intestinal epithelium and deeper organs of the immune system. Microbial ligands and activities are detected by host sensors that elicit a range of immune responses. Membrane-bound toll-like receptors and cytosolic inflammasome pathways are key signal transducers that trigger the production of pro-inflammatory molecules, such as cytokines and chemokines, and regulate cell death in response to infection. In recent years, the inflammasomes have emerged as a key frontier in the tussle between bacterial pathogens and the host. Inflammasomes are complexes that activate caspase-1 and are regulated by related caspases, such as caspase-11, -4, -5 and -8. Importantly, enteric bacterial pathogens can actively engage or evade inflammasome signalling systems. Extracellular, vacuolar and cytosolic bacteria have developed divergent strategies to subvert inflammasomes. While some pathogens take advantage of inflammasome activation (e.g. Listeria monocytogenes, Helicobacter pylori), others (e.g. E. coli, Salmonella, Shigella, Yersinia sp.) deploy a range of virulence factors, mainly type 3 secretion system effectors, that subvert or inhibit inflammasomes. In this review we focus on inflammasome pathways and their immune functions, and discuss how enteric bacterial pathogens interact with them. These studies have not only shed light on inflammasome-mediated immunity, but also the exciting area of mammalian cytosolic immune surveillance.

Functional characterization of a broad and potent neutralizing monoclonal antibody directed against outer membrane protein (OMP) of Salmonella typhimurium.

In the present study, we have generated a murine monoclonal antibody (mAb) named Sal-06 by using the crude outer membrane protein preparation of Salmonella enteric subsp. enterica serovar Typhimurium ATCC 14028 strain as antigen. Sal-06mAb belonging to IgG1 isotype demonstrated broad cross-reactivity to standard and isolated strains of genus Salmonella and others such as Escherichia coli, Klebsiella pneumonia, and Proteus mirabilis. Cross-reactivity across several bacterial genera indicated that the epitopes reactive to Sal-06mAb are conserved among these members. Neutralizing effects of Sal-06mAb on Salmonella growth and survival was evaluated in vitro using bacteriostatic and bactericidal activity with and without complement and bacterial invasion inhibition assay. Sal-06mAb demonstrated a bacteriostatic effect on the growth of S. typhimurium ATCC 14028 strain which is both time and concentration (of mAb) dependent. It was also found that the bacterial growth inhibition was complement independent. When the bacterial cells were preincubated with Sal-06mAb, it reduced the adherence and invasion of bacterial cells into A549 epithelial cell line. This was confirmed by CFU count analysis, phase contrast, and fluorescence microscopy. Scanning electron microscope (SEM) imaging confirmed the antimicrobial effects of Sal-06mAb on S. typhimurium ATCC 14028. The development of broadly reactive and cross protective Sal-06mAb opens new possibilities for immunotherapy of sepsis caused by Gram-negative Enterobacteriaceae members.

Prevalence of non-extended spectrum ß-lactamases SHV-1 and TEM-1 or -2 types in multidrug-resistant Enterobacteriaceae in northern Iran.

The present study aimed to evaluate TEM-1 or -2 and SHV-1 ß-lactamases frequency in multidrug-resistant (MDR) Enterobacteriaceae isolated from patients' urine in northern Iran. The resistance pattern to 20 antibiotics and ESBL production in 200 MDR Enterobacteriaceae was detected using the disk diffusion test and double-disk synergy test (DDST), respectively. Multiplex PCR was applied to detect blaTEM-1 or -2 and blaSHV genes in isolates. DDST findings were inconsistent with multiplex PCR results. The distribution of each of blaTEM-1 or -2 and blaSHV genes, either alone or in combination, in the ESBL-producing isolates was higher than the non-ESBL-producing isolates. There was a significant effect of the presence of blaTEM-1 or -2 gene on resistance to cephalotin at the p < 0.01 level and cefepime, tetracycline, and streptomycin at the P < 0.05 level, and the presence of blaSHV-1 gene on resistance to fosfomycin at the P < 0.05 level as well as the presence both blaTEM-1 or -2 and blaSHV-1 genes on resistance to cephalotin and fosfomycin at the P < 0.01 level. In all isolates, ESBL production, except for cephalotin resistance, did not improve resistance to other antibiotics used and even non-ESBL-producing isolates showed higher resistance to antibiotics compared to ESBL-producing isolates. It seems that mechanisms other than production of ESBL to be involved as part of the resistance mechanisms of the studied isolates against the used antibiotics. For epidemiological studies, both phenotypic and molecular tests must be included to identify the blaTEM-1 or -2 and blaSHV-1 genotypes to ensure infection prevention and control.

Bacterial MgrB peptide activates chemoreceptor Fpr3 in mouse accessory olfactory system and drives avoidance behaviour.

Innate immune chemoreceptors of the formyl peptide receptor (Fpr) family are expressed by vomeronasal sensory neurons (VSNs) in the accessory olfactory system. Their biological function and coding mechanisms remain unknown. We show that mouse Fpr3 (Fpr-rs1) recognizes the core peptide motif f-MKKFRW that is predominantly present in the signal sequence of the bacterial protein MgrB, a highly conserved regulator of virulence and antibiotic resistance in Enterobacteriaceae. MgrB peptide can be produced and secreted by bacteria, and is selectively recognized by a subset of VSNs. Exposure to the peptide also stimulates VSNs in freely behaving mice and drives innate avoidance. Our data shows that Fpr3 is required for neuronal detection and avoidance of peptides derived from a conserved master virulence regulator of enteric bacteria.

Recurrent urinary tract infections caused by Raoultella planticola after kidney transplant.

Recurrent urinary tract infections are difficult to manage in patients with a history of kidney transplant and may contribute to graft loss. Few cases describe recurrent urinary tract infections due to Raoultella planticola in this population. We describe the management of recurrent urinary tract infections due to R planticola in a kidney transplant recipient and review other case reports of urinary tract infections due to this organism.

Yokenella regensburgei necrotizing fasciitis in an immunocompromised host.

We report a case of necrotizing skin infection caused by Yokenella regensburgei in an immunosuppressed patient with orthotopic liver transplantation. Initial bacterial culture identification was suggestive of Hafnia alvei. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) confirmed identification of Y. regensburgei. Necrotizing fasciitis is potentially fatal and requires aggressive management, including early diagnosis, appropriate antibiotic selection, and operative debridement.

Mechanisms of Type I-E and I-F CRISPR-Cas Systems in Enterobacteriaceae.

CRISPR-Cas systems provide bacteria and archaea with adaptive immunity against invasion by bacteriophages and other mobile genetic elements. Short fragments of invader DNA are stored as immunological memories within CRISPR (clustered regularly interspaced short palindromic repeat) arrays in the host chromosome. These arrays provide a template for RNA molecules that can guide CRISPR-associated (Cas) proteins to specifically neutralize viruses upon subsequent infection. Over the past 10 years, our understanding of CRISPR-Cas systems has benefited greatly from a number of model organisms. In particular, the study of several members of the Gram-negative Enterobacteriaceae family, especially Escherichia coli and Pectobacterium atrosepticum, have provided significant insights into the mechanisms of CRISPR-Cas immunity. In this review, we provide an overview of CRISPR-Cas systems present in members of the Enterobacteriaceae. We also detail the current mechanistic understanding of the type I-E and type I-F CRISPR-Cas systems that are commonly found in enterobacteria. Finally, we discuss how phages can escape or inactivate CRISPR-Cas systems and the measures bacteria can enact to counter these types of events.

What can a weevil teach a fly, and reciprocally? Interaction of host immune systems with endosymbionts in Glossina and Sitophilus.

The tsetse fly (Glossina genus) is the main vector of African trypanosomes, which are protozoan parasites that cause human and animal African trypanosomiases in Sub-Saharan Africa. In the frame of the IAEA/FAO program 'Enhancing Vector Refractoriness to Trypanosome Infection', in addition to the tsetse, the cereal weevil Sitophilus has been introduced as a comparative system with regards to immune interactions with endosymbionts. The cereal weevil is an agricultural pest that destroys a significant proportion of cereal stocks worldwide. Tsetse flies are associated with three symbiotic bacteria, the multifunctional obligate Wigglesworthia glossinidia, the facultative commensal Sodalis glossinidius and the parasitic Wolbachia. Cereal weevils house an obligatory nutritional symbiosis with the bacterium Sodalis pierantonius, and occasionally Wolbachia. Studying insect host-symbiont interactions is highly relevant both for understanding the evolution of symbiosis and for envisioning novel pest control strategies. In both insects, the long co-evolution between host and endosymbiont has led to a stringent integration of the host-bacteria partnership. These associations were facilitated by the development of specialized host traits, including symbiont-housing cells called bacteriocytes and specific immune features that enable both tolerance and control of the bacteria. In this review, we compare the tsetse and weevil model systems and compile the latest research findings regarding their biological and ecological similarities, how the immune system controls endosymbiont load and location, and how host-symbiont interactions impact developmental features including cuticle synthesis and immune system maturation. We focus mainly on the interactions between the obligate symbionts and their host's immune systems, a central theme in both model systems. Finally, we highlight how parallel studies on cereal weevils and tsetse flies led to mutual discoveries and stimulated research on each model, creating a pivotal example of scientific improvement through comparison between relatively distant models.

Enteric bacteria boost defences against oxidative stress in Entamoeba histolytica.

Oxidative stress is one of the strongest toxic factors in nature: it can harm or even kill cells. Cellular means of subverting the toxicity of oxidative stress are important for the success of infectious diseases. Many types of bacterium inhabit the intestine, where they can encounter pathogens. During oxidative stress, we analyzed the interplay between an intestinal parasite (the pathogenic amoeba Entamoeba histolytica - the agent of amoebiasis) and enteric bacteria (microbiome residents, pathogens and probiotics). We found that live enteric bacteria protected E. histolytica against oxidative stress. By high-throughput RNA sequencing, two amoebic regulatory modes were observed with enteric bacteria but not with probiotics. The first controls essential elements of homeostasis, and the second the levels of factors required for amoeba survival. Characteristic genes of both modes have been acquired by the amoebic genome through lateral transfer from the bacterial kingdom (e.g. glycolytic enzymes and leucine-rich proteins). Members of the leucine-rich are homologous to proteins from anti-bacterial innate immune such as Toll-like receptors. The factors identified here suggest that despite its old age in evolutionary terms, the protozoan E. histolytica displays key characteristics of higher eukaryotes' innate immune systems indicating that components of innate immunity existed in the common ancestor of plants and animals.

Changes in Caenorhabditis elegans gene expression following exposure to Photorhabdus luminescens strain TT01.

Photorhabdus bacteria enter into a mutualistic symbiosis with Heterorhabditis nematodes to infect insect larvae. However, they rapidly kill the model nematode Caenorhabditis elegans. One hypothesis for these divergent outcomes is that the nematode defense responses differ. To begin testing this hypothesis, we have systematically analyzed available data on the transcriptional response of C. elegans to P. luminescens strain Hb. From a starting pool of over 7000 differentially expressed genes, we carefully chose 21 Heterorhabditis-conserved genes to develop as comparative markers. Using newly designed and validated qRT-PCR primers, we measured expression of these genes in C. elegans exposed to the sequenced TT01 strain of P. luminescens, on two different media types. Almost all (18/21) of the genes showed a significant response to P. luminescens strain TT01. One response is dependent on media type, and a subset of genes may respond differentially to distinct strains. Overall, we have established useful resources and generated new hypotheses regarding how C. elegans responds to P. luminescens infection.

Is a Human CD8 T-Cell Vaccine Possible, and if So, What Would It Take? CD8 T-Cell-Mediated Protective Immunity and Vaccination against Enteric Bacteria.

Although induction of CD8+ responses is widely accepted as critical in clearing viral infections and necessary for effective vaccines against viruses, much less is known regarding the role of these cells in bacterial and other infections, particularly those that enter the host via the gastrointestinal tract. In this commentary, I discuss the likelihood that CD8+ responses are also important in protection from intestinal Gram-negative bacteria, as well as the many factors that should be taken into consideration during the development of vaccines, based on eliciting long-term protection predominantly mediated by CD8+ responses against these organisms.