Mucosally-directed adrenergic nerves and sympathomimetic drugs enhance non-intimate adherence of Escherichia coli O157:H7 to porcine cecum and colon

Reducing Weaning Stress in Piglets by Pre-Weaning Socialization and Gradual Separation from the Sow: A Review

The weaning of pigs in most commercial pork production systems is an abrupt event performed at a fairly young age, i.e., mostly between 2.5 and 5 weeks of age. This practice induces a stress response, and its impact on behavior, performance and the gastrointestinal tract has been well described. Historically, there has been a focus on pre- and post-weaning nutritional strategies and post-weaning housing conditions and medication to improve production and reduce mortality after weaning. However, alternative pre-weaning housing and management systems that promote the development of natural social behaviors of piglets before weaning have recently received more attention. Co-mingling of non-littermates before weaning is a strategy that aims to initiate social interactions prior to weaning. The separation of the litter from the sow in the period leading up to weaning, termed intermittent suckling, aims to enhance the gradual separation from the sow. In addition, these practices encourage the young pig to learn explorative nutrient sourcing. Altogether, they may reduce weaning-associated stress. In this review, these strategies are defined, and their effects on behavior, performance, mortality, gastrointestinal function and immunocompetence are described. Though these strategies may be adapted to a commercial setting, it also becomes clear that many factors can contribute to the success of these strategies.

Pathophysiologic Role of Neurotransmitters in Digestive Diseases

Neurotransmitters are special molecules that serve as messengers in chemical synapses between neurons, cells, or receptors, including catecholamines, serotonin, dopamine, and other neurotransmitters, which play an important role in both human physiology and pathology. Compelling evidence has indicated that neurotransmitters have an important physiological role in various digestive diseases. They act as ligands in combination with central or peripheral receptors, and transmits signals through chemical synapses, which are involved in regulating the physiological and pathological processes of the digestive tract organs. For instance, neurotransmitters regulate blood circulation and affect intestinal movement, nutrient absorption, the gastrointestinal innate immune system, and the microbiome. In this review, we will focus on the role of neurotransmitters in the pathogenesis of digestive tract diseases to provide novel therapeutic targets for new drug development in digestive diseases.

Azadirachtin directly or indirectly affects the abundance of intestinal flora of Spodoptera litura and the energy conversion of intestinal contents mediates the energy balance of intestine-brain axis, and along with decreased expression CREB in the brain neurons

Azadirachtin is a good growth inhibitor for Lepidopteran larvae, but its effect on the brain neurons, intestinal flora and intestinal contents caused by the growth inhibition mechanism has not been reported yet. This study explored the mechanism of azadirachtin on the growth and development of Spodoptera litura larvae and brain neurons through three aspects: intestinal pathology observation, intestinal flora sequencing, and intestinal content analysis. The results showed that the treatment of azadirachtin led to the pathological changes in the structure of the midgut and the goblet cells in the intestinal wall cells to undergo apoptosis. Changes in the host environment of the intestinal flora lead to changes in the abundance value of the intestinal flora, showing an increase in the abundance value of harmful bacteria such as Sphingomonas and Enterococcus, as well as an increase in the abundance value of excellent flora such as Lactobacillus and Bifidobacterium. Changes in the abundance of intestinal flora will result in changes in intestinal contents and metabolites. The test results show that after azadirachtin treatment, the alkane compounds in the intestinal contents of the larvae are greatly reduced, and the number of the long carbon chain and multi-branched hydrocarbon compounds is increased, unsaturated fatty acids, silicon‑oxygen compounds and ethers. The production of similar substances indicates that azadirachtin has an inhibitory effect on digestive enzymes in the intestines, which results in the inhibition of substance absorption and energy transmission, and ultimately the inhibition of larval growth and brain neurons.

Nutritional Regulation of Gut Barrier Integrity in Weaning Piglets

Simple Summary

Weaning is a very stressful period in the piglet’s life in intensive farming: it is a sudden process occurring between three to four weeks of age, when the gastrointestinal tract (GIT) is still immature. The GIT is formed by the epithelial, immune and enteric nervous system which controls epithelial barrier integrity as well as gut functions including the transport of luminal nutrients, water and electrolytes. Early weaning is characterized by a breakdown of these gut functions, an increase in intestinal permeability and the appearance of gastrointestinal functional disorders, which can have long-lasting consequences in the pig’s life. Weaning, therefore, requires the correct level of nutrients, high quality ingredients, and management, which are directed primarily at encouraging rapid feed intake whilst reducing mortality and morbidity. This review describes the organization of the GIT and highlights the interactions between feed components and the morphology and physiology of the epithelial barrier. Novel dietary strategies focused on improving gut health are also discussed, considering the impacts of selected feed ingredients or additives on the GIT such as functional amino acids, phytochemicals and organic acids.

Abstract

Weaning is very stressful for piglets and leads to alterations in the intestinal barrier, a reduction in nutrient absorption and a higher susceptibility to intestinal diseases with heavy economic losses. This review describes the structures involved in the intestinal barrier: the epithelial barrier, immune barrier and the enteric nervous system. Here, new insights into the interactions between feed components and the physiology and morphology of the epithelial barrier are highlighted. Dietary strategies focused on improving gut health are also described including amino acids, phytochemicals and organic acids.

Review: Microbial endocrinology: intersection of microbiology and neurobiology matters to swine health from infection to behavior

From birth to slaughter, pigs are in constant interaction with microorganisms. Exposure of the skin, gastrointestinal and respiratory tracts, and other systems allows microorganisms to affect the developmental trajectory and function of porcine physiology as well as impact behavior. These routes of communication are bi-directional, allowing the swine host to likewise influence microbial survival, function and community composition. Microbial endocrinology is the study of the bi-directional dialogue between host and microbe. Indeed, the landmark discovery of host neuroendocrine systems as hubs of host-microbe communication revealed neurochemicals act as an inter-kingdom evolutionary-based language between microorganism and host. Several such neurochemicals are stress catecholamines, which have been shown to drastically increase host susceptibility to infection and augment virulence of important swine pathogens, including Clostridium perfringens. Catecholamines, the production of which increase in response to stress, reach the epithelium of multiple tissues, including the gastrointestinal tract and lung, where they initiate diverse responses by members of the microbiome as well as transient microorganisms, including pathogens and opportunistic pathogens. Multiple laboratories have confirmed the evolutionary role of microbial endocrinology in infectious disease pathogenesis extending from animals to even plants. More recent investigations have now shown that microbial endocrinology also plays a role in animal behavior through the microbiota-gut-brain axis. As stress and disease are ever-present, intersecting concerns during each stage of swine production, novel strategies utilizing a microbial endocrinology-based approach will likely prove invaluable to the swine industry.

Relationship between the gut microbiome and brain function

It has become increasingly evident in recent years that the gut microbiome and the brain communicate in a bidirectional manner, with each possibly affecting the other's functions. Substantial research has aimed to understand the mechanisms of this interaction and to outline strategies for preventing or treating nervous system-related disturbances. This review explores the evidence demonstrating how the gut microbiome may affect brain function in adults, thereby having an impact on stress, anxiety, depression, and cognition. In vitro, in vivo, and human studies reporting an association between a change in the gut microbiome and functional changes in the brain are highlighted, as are studies outlining the mechanisms by which the brain affects the microbiome and the gastrointestinal tract. Possible modes of action to explain how the gut microbiome and the brain functionally affect each other are proposed. Supplemental probiotics to combat brain-related dysfunction offer a promising approach, provided future research elucidates their mode of action and possible side effects. Further studies are warranted to establish how pre- and probiotic interventions may help to balance brain function in healthy and diseased individuals.

Modulation of Enterohaemorrhagic Escherichia coli Survival and Virulence in the Human Gastrointestinal Tract

Enterohaemorrhagic Escherichia coli (EHEC) is a major foodborne pathogen responsible for human diseases ranging from diarrhoea to life-threatening complications. Survival of the pathogen and modulation of virulence gene expression along the human gastrointestinal tract (GIT) are key features in bacterial pathogenesis, but remain poorly described, due to a paucity of relevant model systems. This review will provide an overview of the in vitro and in vivo studies investigating the effect of abiotic (e.g., gastric acid, bile, low oxygen concentration or fluid shear) and biotic (e.g., gut microbiota, short chain fatty acids or host hormones) parameters of the human gut on EHEC survival and/or virulence (especially in relation with motility, adhesion and toxin production). Despite their relevance, these studies display important limitations considering the complexity of the human digestive environment. These include the evaluation of only one single digestive parameter at a time, lack of dynamic flux and compartmentalization, and the absence of a complex human gut microbiota. In a last part of the review, we will discuss how dynamic multi-compartmental in vitro models of the human gut represent a novel platform for elucidating spatial and temporal modulation of EHEC survival and virulence along the GIT, and provide new insights into EHEC pathogenesis.

The stress hormone norepinephrine increases the growth and virulence of Aeromonas hydrophila

Stress is an important contributing factor in the outbreak of infectious fish diseases. To comprehensively understand the impact of catecholamine stress hormone norepinephrine (NE) on the pathogenicity of Aeromonas hydrophila, we assessed variations in bacterial growth, virulence‐related genes expression and virulence factors activity after NE addition in serum‐SAPI medium. Further, we assessed the effects of NE on A. hydrophila virulence in vivo by challenging fish with pathogenic strain AH196 and following with or without NE injection. The NE‐associated stimulation of A. hydrophila strain growth was not linear‐dose‐dependent, and only 100 μM, or higher concentrations, could stimulate growth. Real‐time PCR analyses revealed that NE notably changed 13 out of the 16 virulence‐associated genes (e.g. ompW, ahp, aha, ela, ahyR, ompA, and fur) expression, which were all significantly upregulated in A. hydrophila AH196 (p < 0.01). NE could enhance the protease activity, but not affect the lipase activity, hemolysis, and motility. Further, the mortality of crucian carp challenged with A. hydrophila AH196 was significantly higher in the group treated with NE (p < 0.01). Collectively, our results showed that NE enhanced the growth and virulence of pathogenic bacterium A. hydrophila.

Symposium review: Microbial endocrinology-Why the integration of microbes, epithelial cells, and neurochemical signals in the digestive tract matters to ruminant health

The union of microbiology and neurobiology, which has been termed microbial endocrinology, is defined as the study of the ability of microorganisms to produce and respond to neurochemicals that originate either within the microorganisms themselves or within the host they inhabit. It serves as the basis for an evolutionarily derived method of communication between a host and its microbiota. Mechanisms elucidated by microbial endocrinology give new insight into the ways the microbiota can affect host stress, metabolic efficiency, resistance to disease, and other factors that may prove relevant to the dairy industry.

Catecholamine-Modulated Novel Surface-Exposed Adhesin LIC20035 of Leptospira spp. Binds Host Extracellular Matrix Components and Is Recognized by the Host during Infection

In this study, the effect of the host stress hormone catecholamine on Leptospira gene transcripts encoding outer membrane proteins was investigated. There was no impact of catecholamine supplementation on the in vitro growth pattern of Leptospira interrogans; however, 7 genes out of 41 were differentially transcribed, and the effect was reversed to the basal level in the presence of the antagonist propranolol. Comprehensive analysis of one of the differentially regulated proteins, LIC20035 (in serovar Copenhageni)/LB047 (in serovar Lai) (due to catecholamine supplementation), revealed immunogenicity and ability to adhere to host extracellular matrices. Protease accessibility assay and phase partition of integral membrane proteins of Leptospira showed LIC20035/LB047 to be an outer membrane surface-exposed protein. The recombinant LIC20035 protein can be serologically detected using human/bovine sera positive for leptospirosis. Moreover, the recombinant LIC20035 can bind to diverse host extracellular matrices, with a higher affinity toward collagen and chondroitin sulfate.IMPORTANCE Leptospirosis is a neglected tropical disease of global importance. This study aimed to identify outer membrane proteins of pathogenic Leptospira responding to host chemical signals like catecholamines, with the potential to serve as virulence factors, new serodiagnostic antigens, and vaccine candidates. This study mimicked the plausible means by which Leptospira during infection and hormonal stress intercepts host catecholamines to disseminate in host tissues.

Weaning stress and gastrointestinal barrier development: Implications for lifelong gut health in pigs

The gastrointestinal (GI) barrier serves a critical role in survival and overall health of animals and humans. Several layers of barrier defense mechanisms are provided by the epithelial, immune and enteric nervous systems. Together they act in concert to control normal gut functions (e.g., digestion, absorption, secretion, immunity, etc.) whereas at the same time provide a barrier from the hostile conditions in the luminal environment. Breakdown of these critical GI functions is a central pathophysiological mechanism in the most serious GI disorders in pigs. This review will focus on the development and functional properties of the GI barrier in pigs and how common early life production stressors, such as weaning, can alter immediate and long-term barrier function and disease susceptibility. Specific stress-related pathophysiological mechanisms responsible for driving GI barrier dysfunction induced by weaning and the implications to animal health and performance will be discussed.

Microbial Endocrinology in the Pathogenesis of Infectious Disease

Microbial endocrinology represents the intersection of two seemingly disparate fields, microbiology and neurobiology, and is based on the shared presence of neurochemicals that are exactly the same in host as well as in the microorganism. The ability of microorganisms to not only respond to, but also produce, many of the same neurochemicals that are produced by the host, such as during periods of stress, has led to the introduction of this evolutionary-based mechanism which has a role in the pathogenesis of infectious disease. The consideration of microbial endocrinology-based mechanisms has demonstrated, for example, that the prevalent use of catecholamine-based synthetic drugs in the clinical setting contributes to the formation of biofilms in indwelling medical devices. Production of neurochemicals by microorganisms most often employs the same biosynthetic pathways as those utilized by the host, indicating that acquisition of host neurochemical-based signaling system in the host may have been acquired due to lateral gene transfer from microorganisms. That both host and microorganism produce and respond to the very same neurochemicals means that there is bidirectionality contained with the theoretical underpinnings of microbial endocrinology. This can be seen in the role of microbial endocrinology in the microbiota-gut-brain axis and its relevance to infectious disease. Such shared pathways argue for a role of microorganism-neurochemical interactions in infectious disease.

Role of the Intestinal Microbiota in Host Responses to Stressor Exposure

Humans have coevolved over time to not only tolerate but also rely on trillions of microbes that aid in the development of our immune system, provide nutrients, break down potentially noxious substances, and act as a barrier against potentially pathogenic organisms. These microbes, collectively known as the microbiota, live in relatively stable communities on mucosal surfaces such as the respiratory tract and gastrointestinal tract. Changes to the microbiota are often transient, due to changes in diet, antibiotic exposure, and psychological stressor exposure. This chapter will discuss how psychological stressors can shape the intestinal microbial community and how these perturbations can contribute to stressor-induced changes in immune function, neurodevelopment, and behavioral deficits.

Large Animal Models: The Key to Translational Discovery in Digestive Disease Research

Gastrointestinal disease is a prevalent cause of morbidity and mortality and the use of animal models have been instrumental in studying mechanisms of digestive pathophysiology. As investigators attempt to translate the wealth of basic science information developed from rodent, models, large animal models provide a number of translational advantages. The pig, in particular, is arguably one of the most powerful models of human organ systems, including the gastrointestinal tract. The pig has provided important tools and insight into intestinal ischemia/reperfusion injury, intestinal mucosal repair, as well as new insights into esophageal injury and repair. Porcine model development has taken advantage of the size of the animal, allowing increased surgical and endoscopic access. In addition, cellular tools such as the intestinal porcine epithelial cell line and porcine enteroids are providing the methodology to translate basic science findings using in-depth mechanistic analyses. Further opportunities in porcine digestive disease modeling include developing additional transgenic pig strains. Collectively, porcine models hold great promise for the future of clinically relevant digestive disease research.

Microbe-host interactions: Influence of the gut microbiota on the enteric nervous system

The enteric nervous system (ENS), considered a separate branch of the autonomic nervous system, is located throughout the length of the gastrointestinal (GI) tract as a series of interconnected ganglionated plexi. Given the proximity of the intestinal microbiota to the ENS, it is perhaps not surprising that the gut microbiota can influence its development and function. However, these interactions are complex and may be either direct or indirect, often involving signalling initiated by microbe-derived components, metabolites or host-derived intermediaries which subsequently affect enteric nerve excitability and GI function. Individual microbes and strains can differentially influence ENS activity and neurochemistry. In this review we will briefly summarise the role of the microbiota on ENS development, and, in some more detail, explore the mechanisms by which the microbiota can influence ENS activity and function.

Catecholamines for inflammatory shock: a Jekyll-and-Hyde conundrum

Catecholamines are endogenous neurosignalling mediators and hormones. They are integral in maintaining homeostasis by promptly responding to any stressor. Their synthetic equivalents are the current mainstay of treatment in shock states to counteract myocardial depression and/or vasoplegia. These phenomena are related in large part to decreased adrenoreceptor sensitivity and altered adrenergic signalling, with resultant vascular and cardiomyocyte hyporeactivity. Catecholamines are predominantly used in supraphysiological doses to overcome these pathological consequences. However, these adrenergic agents cause direct organ damage and have multiple 'off-target' biological effects on immune, metabolic and coagulation pathways, most of which are not monitored or recognised at the bedside. Such detrimental consequences may contribute negatively to patient outcomes. This review explores the schizophrenic 'Jekyll-and-Hyde' characteristics of catecholamines in critical illness, as they are both necessary for survival yet detrimental in excess. This article covers catecholamine physiology, the pleiotropic effects of catecholamines on various body systems and pathways, and potential alternatives for haemodynamic support and adrenergic modulation in the critically ill.

Modulation of the Interaction of Enteric Bacteria with Intestinal Mucosa by Stress-Related Catecholamines

Stress associated with parturition, transport or mixing has long been correlated with enhanced faecal excretion of diarrhoeal zoonotic pathogens in animals such as Salmonella enterica and Escherichia coli. It may also predispose humans to infection and/or be associated with more severe outcomes. One possible explanation for this phenomenon is the ability of enteric bacterial pathogens to sense and respond to host stress-related catecholamines. This article reviews evidence of the ability of catecholamine hormones to modulate interactions between Gram-negative diarrhoeal pathogens and intestinal mucosa, as well as the molecular mechanisms that may be at work.

Porcine models of digestive disease: the future of large animal translational research

There is increasing interest in nonrodent translational models for the study of human disease. The pig, in particular, serves as a useful animal model for the study of pathophysiological conditions relevant to the human intestine. This review assesses currently used porcine models of gastrointestinal physiology and disease and provides a rationale for the use of these models for future translational studies. The pig has proven its utility for the study of fundamental disease conditions such as ischemia-reperfusion injury, stress-induced intestinal dysfunction, and short bowel syndrome. Pigs have also shown great promise for the study of intestinal barrier function, surgical tissue manipulation and intervention, as well as biomaterial implantation and tissue transplantation. Advantages of pig models highlighted by these studies include the physiological similarity to human intestine and mechanisms of human disease. Emerging future directions for porcine models of human disease include the fields of transgenics and stem cell biology, with exciting implications for regenerative medicine.

Microbial endocrinology: host-bacteria communication within the gut microbiome

The human body is home to trillions of micro-organisms, which are increasingly being shown to have significant effects on a variety of disease states. Evidence exists that a bidirectional communication is taking place between us and our microbiome co-habitants, and that this dialogue is capable of influencing our health in a variety of ways. This review considers how host hormonal signals shape the microbiome, and what in return the microbiome residents may be signalling to their hosts.

Morphine attenuates apically-directed cytokine secretion from intestinal epithelial cells in response to enteric pathogens

Epithelial cells represent the first line of host immune defense at mucosal surfaces. Although opioids appear to increase host susceptibility to infection, no studies have examined opioid effects on epithelial immune functions. We tested the hypothesis that morphine alters vectorial cytokine secretion from intestinal epithelial cell (IPEC-J2) monolayers in response to enteropathogens. Both entero-adherent Escherichia coli O157:H7 and entero-invasive Salmonella enterica serovar Typhimurium increased apically-directed IL-6 secretion and bi-directional IL-8 secretion from epithelial monolayers, but only IL-6 secretion evoked by E. coli was reduced by morphine acting through a naloxone-sensitive mechanism. Moreover, the respective type 4 and 5 Toll-like receptor agonists, lipopolysaccharide and flagellin, increased IL-8 secretion from monolayers, which was also attenuated by morphine pretreatment. These results suggest that morphine decreases cytokine secretion and potentially phagocyte migration and activation directed towards the mucosal surface; actions that could increase host susceptibility to some enteric infections.

Transit effects on fecal Escherichia coli O157 prevalence and coliform concentrations in feedlot cattle

Our objectives were to evaluate the effects of transportation and lairage on fecal shedding of Escherichia coli O157 (E. coli O157), total Escherichia coli, and total coliforms in feedlot cattle, and the relationships between E. coli O157 prevalence and total E. coli population. The study was a randomized complete block design with a split-plot including 2 treatments: a nontransported group, which remained in its pen at all times, and a transported group, which was transported for 1 h in a trailer and subsequently unloaded in a different pen. The experiment was repeated on 3 different days (blocking factor) with 20 steers/d (10 steers/treatment, 60 total). Fecal samples were taken pretransport (h 0) and after 4 and 28 h, lairage from freshly voided fecal pats were taken from each animal. One gram of feces was transferred to a PBS tube, serially diluted, and plated onto Petrifilm for enumeration of total coliforms. Another sample (1 g) was added to gram-negative broth containing cefixime, cefsulodin, and vancomycin, and subjected to immunomagnetic separation. Resulting beads were plated onto MacConkey agar with sorbitol, cefixime, and tellurite. Nonsorbitol fermenting colonies were selected and tested for indole production and O157 antigen agglutination. Results were confirmed using an API 20E kit. Prevalence of E. coli O157 was transient across blocks. E. coli O157 prevalence revealed no treatment × sampling time interaction (P = 0.179) or sampling time effect (P = 0.937), but a tendency for a treatment effect (P = 0.092). Numbers of E. coli and other coliforms did not change across blocks. No effect of treatment (P > 0.7) was observed on total E. coli concentrations or total coliforms. However, tendencies for treatment × sampling time interactions were observed on both populations (P < 0.08), as well as a tendency for a sampling time effect on total E. coli (P = 0.087) and an effect on total coliforms (P = 0.004). Prevalence of E. coli O157 was not correlated with the concentration of total E. coli (P = 0.954). Results suggest that shedding of E. coli O157 and coliforms can vary within a period of 29 h. Greater statistical power and pathogen quantification, as well as hide sampling and stress-related measurements, are needed to be able to conclude on the effects of transport stress on E. coli O157 prevalence and the changes undergone in pathogen shedding patterns after transportation.

Severe sepsis facilitates intestinal colonization by extended-spectrum-β-lactamase-producing Klebsiella pneumoniae and transfer of the SHV-18 resistance gene to Escherichia coli during antimicrobial treatment

Infections caused by multidrug-resistant pathogens are frequent and life threatening in critically ill patients. To investigate whether severe sepsis affects gut colonization by resistant pathogens and genetic exchange between opportunistic pathogens, we tested the intestinal-colonization ability of an extended-spectrum beta-lactamase-producing Klebsiella pneumoniae strain carrying the SHV-18 resistance gene and the transfer ability of the resistance gene to endogenous Escherichia coli under ceftriaxone treatment in rats with burn injury only or severe sepsis induced by burns plus endotoxin exposure. Without ceftriaxone treatment, the K. pneumoniae strain colonized the intestine in both septic and burned rats for a short time, with clearance occurring earlier in burn-only rats but never in sham burn rats. In both burned and septic rats, the colonization level of the challenge strain dropped at the beginning and then later increased during ceftriaxone treatment, after which it declined gradually. This pattern coincided with the change in resistance of K. pneumoniae to ceftriaxone during and after ceftriaxone treatment. Compared with burn-only injury, severe sepsis had a more significant effect on the change in antimicrobial resistance to ceftriaxone. Only in septic rats was the resistance gene successfully transferred from the challenge strain to endogenous E. coli during ceftriaxone treatment; the gene persisted for at least 4 weeks after ceftriaxone treatment. We concluded that severe sepsis can facilitate intestinal colonization by an exogenous resistant pathogen and the transfer of the resistance gene to a potential endogenous pathogen during antimicrobial treatment.

Norepinephrine potentiates proinflammatory responses of human vaginal epithelial cells

The vaginal epithelium provides a barrier to pathogens and recruits immune defenses through the secretion of cytokines and chemokines. Several studies have shown that mucosal sites are innervated by norepinephrine-containing nerve fibers. Here we report that norepinephrine potentiates the proinflammatory response of human vaginal epithelial cells to products produced by Staphylococcus aureus, a pathogen that causes menstrual toxic shock syndrome. The cells exhibit immunoreactivity for catecholamine synthesis enzymes and the norepinephrine transporter. Moreover, the cells secrete norepinephrine and dopamine at low concentrations. These results indicate that norepinephrine may serve as an autocrine modulator of proinflammatory responses in the vaginal epithelium.

Communication between Bacteria and Their Hosts

It is clear that a dialogue is occurring between microbes and their hosts and that chemical signals are the language of this interkingdom communication. Microbial endocrinology shows that, through their long coexistence with animals and plants, microorganisms have evolved sensors for detecting eukaryotic hormones, which the microbe uses to determine that they are within proximity of a suitable host and to optimally time the expression of genes needed for host colonisation. It has also been shown that some prokaryotic chemical communication signals are recognized by eukaryotes. Deciphering what is being said during the cross-talk between microbe and host is therefore important, as it could lead to new strategies for preventing or treating bacterial infections.

Stress and microbial endocrinology: prospects for ruminant nutrition

The feed efficiency of ruminant meat and dairy livestock can be significantly influenced by factors within their living environments. In particular, events perceived by the animals as stressful (such as parturition, transport or handling) have been found to affect susceptibility to infection. It has been well documented that even minor stress such as weighing can result in an increase in colonisation and faecal shedding of enteric pathogens such as Salmonella enterica and Escherichia coli O157:H7. Such infections affect both ruminant overall health and therefore performance, and are a particular problem for the meat production industries. Prior explanations for stress enhancing the likelihood of infection is that activation of the sympathetic nervous system under stress leads to the release of neuroendocrine mediators such as the catecholamine stress hormones noradrenaline and adrenaline, which may impair innate and adaptive immunity. More recently, however, another equally compelling explanation, viewed through the lens of the newly recognised microbiological discipline of microbial endocrinology is that the myriad of bacteria within the ruminant digestive tract are as responsive to the hormonal output of stress as the cells of their host. Work from our laboratories has shown that enteric pathogens have evolved systems for directly sensing stress hormones. We have demonstrated that even brief exposure of enteric pathogens to physiological concentrations of stress hormones can result in massive increases in growth and marked changes in expression of virulence factors such as adhesins and toxins. Happy, less stressed ruminants may therefore be better-nourished animals and safer sources of meat. This article reviews evidence that stress, as well as affecting nutrition, in ruminants is correlated with increased risk of enteric bacterial infections, and examines the molecular mechanisms that may be at work in both processes.

Global effects of catecholamines on Actinobacillus pleuropneumoniae gene expression

Bacteria can use mammalian hormones to modulate pathogenic processes that play essential roles in disease development. Actinobacillus pleuropneumoniae is an important porcine respiratory pathogen causing great economic losses in the pig industry globally. Stress is known to contribute to the outcome of A. pleuropneumoniae infection. To test whether A. pleuropneumoniae could respond to stress hormone catecholamines, gene expression profiles after epinephrine (Epi) and norepinephrine (NE) treatment were compared with those from untreated bacteria. The microarray results showed that 158 and 105 genes were differentially expressed in the presence of Epi and NE, respectively. These genes were assigned to various functional categories including many virulence factors. Only 18 genes were regulated by both hormones. These genes included apxIA (the ApxI toxin structural gene), pgaB (involved in biofilm formation), APL_0443 (an autotransporter adhesin) and genes encoding potential hormone receptors such as tyrP2, the ygiY-ygiX (qseC-qseB) operon and narQ-narP (involved in nitrate metabolism). Further investigations demonstrated that cytotoxic activity was enhanced by Epi but repressed by NE in accordance with apxIA gene expression changes. Biofilm formation was not affected by either of the two hormones despite pgaB expression being affected. Adhesion to host cells was induced by NE but not by Epi, suggesting that the hormones affect other putative adhesins in addition to APL_0443. This study revealed that A. pleuropneumoniae gene expression, including those encoding virulence factors, was altered in response to both catecholamines. The differential regulation of A. pleuropneumoniae gene expression by the two hormones suggests that this pathogen may have multiple responsive systems for the two catecholamines.

The complex interplay between stress and bacterial infections in animals

Over the past decade, an increasing awareness has arisen of the role of neuroendocrine hormones in the susceptibility of mammalian hosts to a bacterial infection. During a stress response, glucocorticoids, catecholamines and neuroendocrine factors are released into the circulation of the host. For a long time the effects of stress on the course of an infection have been exclusively ascribed to the direct effect of stress-related hormones on the immune system and the intestinal barrier function. Chronic stress is known to cause a shift from T helper 1-mediated cellular immunity toward T helper 2-mediated humoral immunity, which can influence the course of an infection and/or the susceptibility to a microorganism. Bacteria can however also respond directly to stress-related host signals. Catecholamines can alter growth, motility, biofilm formation and/or virulence of pathogens and commensal bacteria, and as a consequence influence the outcome of infections by these bacteria in many hosts. For some bacteria, such as Salmonella, Escherichia coli and Pseudomonas aeruginosa it was shown that this influence is regulated by quorum sensing mechanisms. In this manuscript an overview of how and when stress influences the outcome of bacterial infections in animals is provided.

Stress at the intestinal surface: catecholamines and mucosa-bacteria interactions

Psychological stress has profound effects on gastrointestinal function, and investigations over the past few decades have examined the mechanisms by which neural and hormonal stress mediators act to modulate gut motility, epithelial barrier function and inflammatory states. With its cellular diversity and large commensal bacterial population, the intestinal mucosa and its overlying mucous environment constitute a highly interactive environment for eukaryotic host cells and prokaryotic bacteria. The elaboration of stress mediators, particularly norepinephrine, at this interface influences host cells engaged in mucosal protection and the bacteria which populate the mucosal surface and gut lumen. This review will address growing evidence that norepinephrine and, in some cases, other mediators of the adaptation to stress modulate mucosal interactions with enteric bacteria. Stress-mediated changes in this delicate interplay may shift the microbial colonization patterns on the mucosal surface and alter the susceptibility of the host to infection. Moreover, changes in host-microbe interactions in the digestive tract may also influence ongoing neural activity in stress-responsive brain areas.

A prospective population-based study of triggers of symptomatic flares in IBD

OBJECTIVES

We aimed to determine whether any of the nonsteroidal anti-inflammatory drugs (NSAIDs), antibiotics, infections, and stress trigger symptomatic flares of inflammatory bowel diseases (IBDs).

METHODS

Participants drawn from a population-based IBD research registry were surveyed every 3 months for 1 year. They simultaneously tracked the use of NSAIDs, antibiotics, infections, major life events, mood, and perceived stress. Social networks, childhood socioeconomic status, and smoking were assessed at baseline. Disease flare was identified using the Manitoba Inflammatory Bowel Disease Index, a validated disease activity index. Across any two consecutive survey periods, participants were categorized as having a flare (inactive/active), having no flare (inactive/inactive), or remaining active (active/active). Potential triggers were evaluated for the first 3-month period to determine predictive rather than concurrent relationships. Data from only one pair of 3-month periods from an individual were analyzed.

RESULTS

A total of 704 participants completed the baseline survey; 552 (78.3%) returned all 5 surveys. In all, 174 participants who had a flare were compared with 209 who had no flare. Perceived stress, negative affect (mood), and major life events were the only trigger variables significantly associated with flares. There were no differences between those who flared and those who did not, in the use of NSAIDs, antibiotics, or in the presence of infections. Multivariate logistic regression analyses indicated that only high-perceived stress (adjusted odds ratio=2.40 (1.35, 4.26)) was associated with an increased risk of flare.

CONCLUSIONS

This study adds to the growing evidence that psychological factors contribute to IBD symptom flares. There was no support for differential rates of use of NSAIDS, antibiotics, or for the occurrence of (non-enteric) infections related to IBD flares.

The participation of the sympathetic innervation of the gastrointestinal tract in disease states

Knowledge of neural circuits, neurotransmitters and receptors involved in the sympathetic regulation of gastrointestinal (GI) function is well established. However, it is only recently that the interaction of sympathetic neurons, and of sympathetic transmitters, with the GI immune system and with gut flora has begun to be explored. Changes in the behaviour of sympathetic nerves when gut function is compromised, for example in ileus and in inflammation, have been observed, but the roles of the sympathetic innervation in these and other pathologies are not adequately understood. In this article, we first review the principal roles of the sympathetic innervation of the GI tract in controlling motility, fluid exchange and gut blood flow in healthy individuals. We then discuss the evidence that there are important interactions of sympathetic transmitters with the gut immune system and enteric glia, and evidence that inflammation has substantial effects on sympathetic neurons. These reciprocal interactions contribute to pathological changes in ways that are not yet clarified. Finally, we focus on inflammation, diabetes and postoperative ileus as conditions in which there is sympathetic involvement in compromised gut function.

Can stress in farm animals increase food safety risk?

All farm animals will experience some level of stress during their lives. Stress reduces the fitness of an animal, which can be expressed through failure to achieve production performance standards, or through disease and death. Stress in farm animals can also have detrimental effects on the quality of food products. However, although a common assumption of a potential effect of stress on food safety exists, little is actually known about how this interaction may occur. The aim of this review was to examine the current knowledge of the potential impact of stress in farm animals on food safety risk. Colonization of farm animals by enteric pathogens such as Escherichia coli O157:H7, Salmonella, and Campylobacter, and their subsequent dissemination into the human food chain are a major public health and economic concern for the food industries. This review shows that there is increasing evidence to demonstrate that stress can have a significant deleterious effect on food safety through a variety of potential mechanisms. However, as the impact of stress is difficult to precisely determine, it is imperative that the issue receives more research attention in the interests of optimizing animal welfare and minimizing losses in product yield and quality, as well as to food safety risks to consumers. While there is some evidence linking stress with pathogen carriage and shedding in farm animals, the mechanisms underlying this effect have not been fully elucidated. Understanding when pathogen loads on the farm are the highest or when animals are most susceptible to infection will help identifying times when intervention strategies for pathogen control may be most effective, and consequently, increase the safety of food of animal origin.

Effect of restraint stress on the population of intestinal intraepithelial lymphocytes in mice

The impact of restraint stress on the intestinal immune system, particularly on intestinal intraepithelial lymphocytes (i-IEL), has not been described in detail. Thus, the purpose of this study was to assess the effects of restraint stress, including those produced by increases in glucocorticoids and catecholamines, on the population of i-IEL. Mice were exposed to 1 or 4h restraint stress for 4 day, and the number of IEL in the mucosa of the proximal small intestine was determined by immunohistochemistry. The effects of restraint were also analyzed in mice submitted to different procedures: adrenalectomy, chemical sympathectomy, and treatment with a glucocorticoid antagonist (RU486), dexamethasone, and epinephrine. The main findings were that: (1) chronic restraint-stress reduced the i-IEl population in the small intestine; (2) adrenalectomy, treatment with RU-486 and chemical sympathectomy decreased the number of gammadelta, CD4+ and CD8+ T cells in non-stressed groups; (3) dexamethasone reduced the number of gammadelta and CD8+ T cells, and (4) epinephrine reduced the number of gammadelta, CD4+ and CD8+ T cells. These results demonstrated that restraint stress decreased the number of i-IEL in the proximal small intestine of mice, mainly by the combined action of higher concentrations of catecholamines and glucocorticoids, and that lower concentrations of glucocorticoids and catecholamines in unstressed mice preserved the population of i-IEL.

Microbial endocrinology: how stress influences susceptibility to infection

A holistic approach to understanding the mechanisms by which stress influences the pathogenesis of infectious disease has resulted in the development of the field of microbial endocrinology. This transdisciplinary field represents the intersection of microbiology with mammalian endocrinology and neurophysiology, and is based on the tenet that microorganisms have evolved systems for using neurohormones, which are widely distributed throughout nature, as environmental cues to initiate growth and pathogenic processes. This review reveals that responsiveness to human stress hormones is widespread in the microbial world and documents recent advances in microbial endocrinology.

Escherichia coliO157:H7 gene expression in the presence of catecholamine norepinephrine

Various forms of host stresses (e.g. physiological, psychological) are thought to influence susceptibility to pathogenic microorganisms. Catecholamines such as norepinephrine are released into the GI environment during acute stress and may influence the infective process of bacterial pathogens associated with the GI tract. To examine the effects of norepinephrine on expression of virulence factors in Escherichia coli O157:H7, the clinical-type isolate EDL933 (ATCC 43895) was grown in serum-Standard American Petroleum Institute media in the presence or absence of norepinephrine. After 5 h of exposure to norepinephrine, treatment and control cultures (not exposed to norepinephrine) were harvested, their RNA isolated, and gene expression evaluated. There was a dramatic increase in the expression of virulence factor transcripts including stx1, stx2, and eae. Also induced were transcripts involved in iron metabolism. Conversely, there was comparative repression of iron acquisition and phage shock protein-related transcripts in the presence of norepinephrine. Novel observations from these data suggested that exposure to norepinephrine induced glutamate decarboxylase acid resistance as well as an SOS response in E. coli O157:H7. The results corroborate many of the previous findings detailed in the literature and provide new observations that could expand the scope of microbial endocrinology.

Stress and bacteria: microbial endocrinology

Regulation of virulence of Campylobacter jejuni by norepinephrine has implications for the husbandry of food production animals and transmission of infection to man

Differential effects of epinephrine, norepinephrine, and indole on Escherichia coli O157:H7 chemotaxis, colonization, and gene expression

During infection in the gastrointestinal tract, enterohemorrhagic Escherichia coli (EHEC) O157:H7 is exposed to a wide range of signaling molecules, including the eukaryotic hormones epinephrine and norepinephrine, and bacterial signal molecules such as indole. Since these signaling molecules have been shown to be involved in the regulation of phenotypes such as motility and virulence that are crucial for EHEC infections, we hypothesized that these molecules also govern the initial recognition of the large intestine environment and attachment to the host cell surface. Here, we report that, compared to indole, epinephrine and norepinephrine exert divergent effects on EHEC chemotaxis, motility, biofilm formation, gene expression, and colonization of HeLa cells. Using a novel two-fluorophore chemotaxis assay, it was found that EHEC is attracted to epinephrine and norepinephrine while it is repelled by indole. In addition, epinephrine and norepinephrine also increased EHEC motility and biofilm formation while indole attenuated these phenotypes. DNA microarray analysis of surface-associated EHEC indicated that epinephrine/norepinephrine up-regulated the expression of genes involved in surface colonization and virulence while exposure to indole decreased their expression. The gene expression data also suggested that autoinducer 2 uptake was repressed upon exposure to epinephrine/norepinephrine but not indole. In vitro adherence experiments confirmed that epinephrine and norepinephrine increased attachment to epithelial cells while indole decreased adherence. Taken together, these results suggest that epinephrine and norepinephrine increase EHEC infection while indole attenuates the process.