Norepinephrine-induced expression of the K99 pilus adhesin of enterotoxigenic Escherichia coli

Effects of Catecholamine Stress Hormones Norepinephrine and Epinephrine on Growth, Antimicrobial Susceptibility, Biofilm Formation, and Gene Expressions of Enterotoxigenic Escherichia coli

Enterotoxigenic Escherichia coli (ETEC) is a significant contributor to diarrhea. To determine whether ETEC-catecholamine hormone interactions contribute to the development of diarrhea, we tested the effects of catecholamine hormones acting on ETEC in vitro. The results showed that in the presence of norepinephrine (NE) and epinephrine (Epi), the growth of 9 out of 10 ETEC isolates was promoted, the MICs of more than 60% of the isolates to 6 antibiotics significantly increased, and the biofilm formation ability of 10 ETEC isolates was also promoted. In addition, NE and Epi also significantly upregulated the expression of the virulence genes feaG, estA, estB, and elt. Transcriptome analysis revealed that the expression of 290 genes was affected by NE. These data demonstrated that catecholamine hormones may augment the diarrhea caused by ETEC.

Informal nutrition symposium: leveraging the microbiome (and the metabolome) for poultry production

Knowledge of gut microbiology of poultry has advanced from a limited ability to culture relatively few microbial species, to attempting to understand the complex interactions between the bird and its microbiome. The Informal Nutrition Symposium 2021 was intended to help poultry scientists to make sense of the implications of the vast amounts of information being generated by researchers. This paper represents a compilation of the talks given at the symposium by leading international researchers in this field. The symposium began with an overview of the historical developments in the field of intestinal microbiology and microbiome research in poultry. Next, the systemic effects of the microbiome on health in the context of the interplay between the intestinal microbiota and the immune system were presented. Because the microbiome and the host communicate and influence each other, the novel field of kinomics (the study of protein phosphorylation) as used in the study of the poultry microbiome was discussed. Protein phosphorylation is a rapid response to the complex of signals among the microbiome, intestinal lumen metabolites, and the host. Then, a description of why an understanding of the role of microbial endocrinology in poultry production can lead to new understanding of the mechanisms by which the gut microbiota and the host can interact in defined mechanisms that ultimately determine health, pathogenesis of infectious disease, and behavior was given. Finally, a view forward was presented underscoring the importance of understanding mechanisms in microbiomes in other organ systems and other species. Additionally, the importance of the development of new -omics platforms and data management tools to more completely understand host microbiomes was stressed.

Gastrointestinal biofilms in health and disease

Microorganisms colonize various ecological niches in the human habitat, as they do in nature. Predominant forms of multicellular communities called biofilms colonize human tissue surfaces. The gastrointestinal tract is home to a profusion of microorganisms with intertwined, but not identical, lifestyles: as isolated planktonic cells, as biofilms and in biofilm-dispersed form. It is therefore of major importance in understanding homeostatic and altered host-microorganism interactions to consider not only the planktonic lifestyle, but also biofilms and biofilm-dispersed forms. In this Review, we discuss the natural organization of microorganisms at gastrointestinal surfaces, stratification of microbiota taxonomy, biogeographical localization and trans-kingdom interactions occurring within the biofilm habitat. We also discuss existing models used to study biofilms. We assess the contribution of the host-mucosa biofilm relationship to gut homeostasis and to diseases. In addition, we describe how host factors can shape the organization, structure and composition of mucosal biofilms, and how biofilms themselves are implicated in a variety of homeostatic and pathological processes in the gut. Future studies characterizing biofilm nature, physical properties, composition and intrinsic communication could shed new light on gut physiology and lead to potential novel therapeutic options for gastrointestinal diseases.

Enterococcus faecium NCIMB10415 responds to norepinephrine by altering protein profiles and phenotypic characters

The long-term established symbiosis between gut microbiota and humans is based upon a dynamic equilibrium that, if unbalanced, could lead to the development of diseases. Despite the huge amount of data concerning the microbiota-gut-brain-axis, little information is available on what happens at the molecular level in bacteria, when exposed to human signals. In the present study, the physiological effects exerted by norepinephrine (NE), a human hormone present in significant amounts in the host gut, were analyzed using the commensal/probiotic strain Enterococcus faecium NCIMB10415 as a target. The aim was to compare the protein profiles of treated and untreated bacteria and relating these proteome patterns to some phenotypic modifications important for bacteria-host interaction. Actually, to date, only pathogens have been considered. Combining a gel-free/label-free proteomic analysis with the evaluation of bile salts resistance, biofilm formation and autoaggregation ability (as well as with the bacterial growth kinetics), allowed to detect changes induced by NE treatment on all the tested probiotic properties. Furthermore, exposure to the bioactive molecule increased the abundance of proteins related to stress response and to host-microbe interaction, such as moonlight proteins involved in adhesion and immune stimulation. The results of this investigation demonstrated that, not only pathogens, but also commensal gut bacteria are affected by host-derived hormones, underlining the importance of a correct cross-signalling in the maintenance of gut homeostasis. SIGNIFICANCE: The crucial role played by the human gut microbiota in ensuring host homeostasis and health is definitively ascertained as suggested by the holobiome concept. The present research was intended to shed light on the endocrinological perturbations possibly affecting microbiota. The microbial model used in this study belongs to Enterococcus faecium species, whose controversial role as gut commensal and opportunistic pathogen in the gut ecosystem is well recognized. The results obtained in the present investigation clearly demonstrate that E. faecium NCIMB10415 can sense and respond to norepinephrine, a human hormone abundant at the gut level, by changing protein profiles and physiology, inducing changes that could favor survival and colonization of the host tissues. To our knowledge, this is the first proteomic report concerning the impact of a human hormone on a commensal/probiotic bacterium, since previous research has focused on exploring the effects of neuroendocrine molecules on growth and virulence of pathogenic species.

Interkingdom Cross-Talk in Times of Stress: Salmonella Typhimurium Grown in the Presence of Catecholamines Inhibits Porcine Immune Functionality in vitro

In stressful situations, catecholamines modulate mammalian immune function, and in addition, they can be sensed by many bacteria. Catecholamine sensing was also found in the zoonotic gut pathogen Salmonella Typhimurium, probably contributing to the stress-induced increased risk of salmonellosis. Virulence traits such as proliferation and invasiveness are promoted upon bacterial catecholamine sensing, but it is unknown whether S. Typhimurium may also inhibit mammalian immune function in stressful situations. We thus investigated whether supernatants from S. Typhimurium grown in the presence of catecholamines modulate porcine mitogen-induced lymphocyte proliferation. Lymphocyte proliferation was reduced by supernatants from catecholamine-exposed Salmonella in a dose-dependent manner. We further examined whether adrenaline oxidation to adrenochrome, which is promoted by bacteria, could be responsible for the observed effect, but this molecule either enhanced lymphocyte functionality or had no effect. We could thereby exclude adrenochrome as a potential immunomodulating agent produced by S. Typhimurium. This study is the first to demonstrate that bacteria grown in the presence of catecholamine stress hormones alter their growth environment, probably by producing immunomodulating substances, in a way that host immune response is suppressed. These findings add a new dimension to interkingdom signaling and provide novel clues to explain the increased susceptibility of a stressed host to Salmonella infection.

Norepinephrine augmented in vitro growth of uropathogenic E. coli in Type 2 diabetes mellitus and its suppression by silodosin (alpha blocker)

Norepinephrine is secreted under conditions of stress in humans. The ability of bacteria to sense mammalian hormone may have a role in propagation of infection. The present study investigated the effect of norepinephrine on in vitro growth of uropathogenic E. coli (UPEC) and the effect of silodosin on norepinephrine-induced changes. The spot urine samples were collected from 56 individuals (14 diabetic patients with UTI, 14 diabetic without UTI, 14 non-diabetic UTI and 14 healthy volunteer controls) for the measurement of urinary norepinephrine concentrations. The concentration of norepinephrine, as found in urine of human subjects, was reproduced in artificial urine medium to study the growth of UPEC. The norepinephrine concentration showing maximum growth response was selected to study the effect of silodosin on the growth inhibition of UPEC. Result showed significantly elevated urinary norepinephrine in diabetic patients with and without UTI and also in nondiabetic UTI groups. The norepinephrine concentration equivalent to that in diabetic UTI patients enhanced the growth of UPEC. Furthermore, silodosin (0.32 μM) inhibited the growth of the UPEC.

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.

Bioconversion of Tyrosine and Tryptophan Derived Biogenic Amines by Neuropathogenic Bacteria

The biochemical potential of pathogenic bacteria may cause alteration in the neurophysiological environment; consequently, neuroendocrine and immune responses of the host are modulated by endogenously produced metabolic products of neuropathogenic bacteria. The present study was designed to detect the derived biogenic amines in spent culture media of Bacillus cereus (Bc), Clostridium tetani (Ct), Listeria monocytogenes (Lm), and Neisseria meningitidis (Nm). Overnight grown culture in different culture media i.e., Nutrient broth (NB), Luria basal broth (LB), Brain Heart Infusion broth (BHI), and human serum supplemented RPMI 1640 medium (RPMI) were used to prepare filter-sterilized, cell-free cultural broths (SCFBs) and subjected to high performance liquid chromatography with electrochemical detection (HPLC-EC) along with the control SCFBs. Comparative analysis of biogenic amines in neuropathogenic bacterial SCFBs with their respective control (SCFB) revealed the complete degradation of dopamine (DA) into its metabolic products by Bc, Ct, and Nm, whereas Lm showed negligible degradation of DA. A relatively high concentration of 5-hydroxyindol acetic acid (5HIAA) by Bc in NB and LB indicated the tryptophan metabolism by the serotonin (5HT) pathway. Our study suggests that microbial endocrinology could help unravel new perspectives to the progression of infectious diseases.

Conversion of Norepinephrine to 3,4-Dihdroxymandelic Acid in Escherichia coli Requires the QseBC Quorum-Sensing System and the FeaR Transcription Factor

The detection of norepinephrine (NE) as a chemoattractant by Escherichia coli strain K-12 requires the combined action of the TynA monoamine oxidase and the FeaB aromatic aldehyde dehydrogenase. The role of these enzymes is to convert NE into 3,4-dihydroxymandelic acid (DHMA), which is a potent chemoattractant sensed by the Tsr chemoreceptor. These two enzymes must be induced by prior exposure to NE, and cells that are exposed to NE for the first time initially show minimal chemotaxis toward it. The induction of TynA and FeaB requires the QseC quorum-sensing histidine kinase, and the signaling cascade requires new protein synthesis. Here, we demonstrate that the cognate response regulator for QseC, the transcription factor QseB, is also required for induction. The related quorum-sensing kinase QseE appears not to be part of the signaling pathway, but its cognate response regulator, QseF, which is also a substrate for phosphotransfer from QseC, plays a nonessential role. The promoter of the feaR gene, which encodes a transcription factor that has been shown to be essential for the expression of tynA and feaB, has two predicted QseB-binding sites. One of these sites appears to be in an appropriate position to stimulate transcription from the P1 promoter of the feaR gene. This study unites two well-known pathways: one for expression of genes regulated by catecholamines (QseBC) and one for expression of genes required for metabolism of aromatic amines (FeaR, TynA, and FeaB). This cross talk allows E. coli to convert the host-derived and chemotactically inert NE into the potent bacterial chemoattractant DHMA.IMPORTANCE The chemotaxis of E. coli K-12 to norepinephrine (NE) requires the conversion of NE to 3,4-dihydroxymandleic acid (DHMA), and DHMA is both an attractant and inducer of virulence gene expression for a pathogenic enterohemorrhagic E. coli (EHEC) strain. The induction of virulence by DHMA and NE requires QseC. The results described here show that the cognate response regulator for QseC, QseB, is also required for conversion of NE into DHMA. Production of DHMA requires induction of a pathway involved in the metabolism of aromatic amines. Thus, the QseBC sensory system provides a direct link between virulence and chemotaxis, suggesting that chemotaxis to host signaling molecules may require that those molecules are first metabolized by bacterial enzymes to generate the actual chemoattractant.

Gram-negative bacterial membrane vesicle release in response to the host-environment: different threats, same trick?

Bacteria are confronted with a multitude of stressors when occupying niches within the host. These stressors originate from host defense mechanisms, other bacteria during niche competition or result from physiological challenges such as nutrient limitation. To counteract these stressors, bacteria have developed a stress-induced network to mount the adaptations required for survival. These stress-induced adaptations include the release of membrane vesicles from the bacterial envelope. Membrane vesicles can provide bacteria with a plethora of immediate and ultimate benefits for coping with environmental stressors. This review addresses how membrane vesicles aid Gram-negative bacteria to cope with host-associated stress factors, focusing on vesicle biogenesis and the physiological functions. As many of the pathways, that drive vesicle biogenesis, confer we propose that shedding of membrane vesicles by Gram-negative bacteria entails an integrated part of general stress responses.

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.

Foodborne enterotoxigenic Escherichia coli: from gut pathogenesis to new preventive strategies involving probiotics

Enterotoxigenic Escherichia coli (ETEC) are a major cause of traveler's diarrhea and infant mortality in developing countries. Given the rise of antibiotic resistance worldwide, there is an urgent need for the development of new preventive strategies. Among them, a promising approach is the use of probiotics. Although many studies, mostly performed under piglet digestive conditions, have shown the beneficial effects of probiotics on ETEC by interfering with their survival, virulence or adhesion to mucosa, underlying mechanisms remain unclear. This review describes ETEC pathogenesis, its modulation by human gastrointestinal cues as well as novel preventive strategies with a particular emphasis on probiotics. The potential of in vitro models simulating human digestion in elucidating probiotic mode of action will be discussed.

What a Dinner Party! Mechanisms and Functions of Interkingdom Signaling in Host-Pathogen Associations

Chemical signaling between cells is an effective way to coordinate behavior within a community. Although cell-to-cell signaling has mostly been studied in single species, it is now appreciated that the sensing of chemical signals across kingdoms can be an important regulator of nutrient acquisition, virulence, and host defense. In this review, we focus on the role of interkingdom signaling in the interactions that occur between bacterial pathogens and their mammalian hosts. We discuss the quorum-sensing (QS) systems and other mechanisms used by these bacteria to sense, respond to, and modulate host signals that include hormones, immune factors, and nutrients. We also describe cross talk between these signaling pathways and strategies used by the host to interfere with bacterial signaling, highlighting the complex bidirectional signaling networks that are established across kingdoms.

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.

Catecholamines promote Actinobacillus pleuropneumoniae growth by regulating iron metabolism

Catecholamines are host stress hormones that can induce the growth of many bacteria by facilitating iron utilization and/or regulate the expression of virulence genes through specific hormone receptors. Whether these two responsive pathways are interconnected is unknown. In our previous study, it was found that catecholamines can regulate the expression of a great number of genes of Actinobacillus pleuropneumoniae, an important swine respiratory pathogen. However, bacterial growth was not affected by catecholamines in rich medium. In this study, it was discovered that catecholamines affected A. pleuropneumoniae growth in chemically defined medium (CDM). We found that serum inhibited A. pleuropneumoniae growth in CDM, while epinephrine, norepinephrine and dopamine promoted A. pleuropneumoniae growth in the CDM containing serum. The known bacterial hormone receptor QseC didn’t play roles in this process. Ion-supplementation and transcriptome analysis indicated that serum addition resulted in iron-restricted conditions which were alleviated by the addition of catecholamines. Transferrin, one of the components in serum, inhibited the growth of A. pleuropneumoniae in CDM, an effect reversed by addition of catecholamines in a TonB2-dependent manner. Our data demonstrate that catecholamines promote A. pleuropneumoniae growth by regulating iron-acquisition and metabolism, which is independent of the adrenergic receptor QseC.

Stress and the commensal microbiota: importance in parturition and infant neurodevelopment

The body is colonized by an enormous array of microbes that are collectively called the microbiota. During quiescent periods, microbial communities within the gut are relatively resistant to change. However, several factors that disrupt homeostasis can also significantly change gut microbial community structure. One factor that has been shown to change the composition of the gut microbiota is exposure to psychological stressors. Studies demonstrate that the commensal microbiota are involved in stressor-induced immunomodulation, but other biological effects are not yet known. This review discusses emerging evidence that the microbiota can impact the brain and behavior and indicates that stressor-induced alterations in the composition of gut microbial communities contribute to stressor-induced behavioral changes. This review will also discuss the evidence that such effects are most evident early in life, where both stress and the microbiota have been linked to birth outcomes, such as prematurity, and neurodevelopment. When considered together, a paradigm emerges in which stressor-induced alterations in commensal microbial populations significantly impact parturition and infant neurodevelopment.

Effect of noradrenaline on the virulence properties of campylobacter species

Campylobacter species cause a spectrum of illnesses in humans. The type of illness and the outcome is dependent on the virulence of the infecting pathogen strain and host immune status. Acute stress can seriously compromise host immunity and increase susceptibility to infection. Noradrenaline (NA) is a stress hormone. Several studies have shown that it stimulated growth and increased the pathogenicity of organisms including E. coli and Campylobacter jejuni. However, the effect of NA on other Campylobacter species is unknown. We have examined the effect of NA on growth rate, motility, invasion of T84 epithelial cells, and colonisation of chickens by diverse Campylobacter species. Campylobacter cultures grown with NA had reduced lag phases, increased growth rates, and higher final optical densities than controls. The motility of Campylobacter was also significantly increased in the presence of noradrenaline. Some of the Campylobacter strains tested also showed increased invasion of T84 epithelial cells, greater breakdown of tight junctions, and an enhanced potential to colonise chickens. Our results show that noradrenaline-induced enhancement of virulence of Campylobacter can influence the outcome of infection.

Microbial endocrinology and the microbiota-gut-brain axis

Microbial endocrinology is defined as the study of the ability of microorganisms to both produce and recognize neurochemicals that originate either within the microorganisms themselves or within the host they inhabit. As such, microbial endocrinology represents the intersection of the fields of microbiology and neurobiology. The acquisition of neurochemical-based cell-to-cell signaling mechanisms in eukaryotic organisms is believed to have been acquired due to late horizontal gene transfer from prokaryotic microorganisms. When considered in the context of the microbiota's ability to influence host behavior, microbial endocrinology with its theoretical basis rooted in shared neuroendocrine signaling mechanisms provides for testable experiments with which to understand the role of the microbiota in host behavior and as importantly the ability of the host to influence the microbiota through neuroendocrine-based mechanisms.

Multidirectional chemical signalling between Mammalian hosts, resident microbiota, and invasive pathogens: neuroendocrine hormone-induced changes in bacterial gene expression

Host-pathogen communication appears to be crucial in establishing the outcome of bacterial infections. There is increasing evidence to suggest that this communication can take place by bacterial pathogens sensing and subsequently responding to host neuroendocrine (NE) stress hormones. Bacterial pathogens have developed mechanisms allowing them to eavesdrop on these communication pathways within their hosts. These pathogens can use intercepted communication signals to adjust their fitness to persist and cause disease in their hosts. Recently, there have been numerous studies highlighting the ability of NE hormones to act as an environmental cue for pathogens, helping to steer their responses during host infection. Host NE hormone sensing can take place indirectly or directly via bacterial adrenergic receptors (BARs). The resulting changes in bacterial gene expression can be of strategic benefit to the pathogen. Furthermore, it is intriguing that not only can bacteria sense NE stress hormones but they are also able to produce key signalling molecules known as autoinducers. The rapid advances in our knowledge of the human microbiome, and its impact on health and disease highlights the potential importance of communication between the microbiota, pathogens and the host. It is indeed likely that the microbiota input significantly in the neuroendocrinological homeostasis of the host by catabolic, anabolic, and signalling processes. The arrival of unwanted guests, such as bacterial pathogens, clearly has a major impact on these delicately balanced interactions. Unravelling the pathways involved in interkingdom communication between invading bacterial pathogens, the resident microbiota, and hosts, may provide novel targets in our continuous search for new antimicrobials to control disease.

Pathogen espionage: multiple bacterial adrenergic sensors eavesdrop on host communication systems

The interactions between bacterial pathogens and their eukaryotic hosts are vital in determining the outcome of infections. Bacterial pathogens employ molecular sensors to detect and facilitate adaptation to changes in their niche. The sensing of these extracellular signals enables the pathogen to navigate within mammalian hosts. Intercellular bacterial communication is facilitated by the production and sensing of autoinducer (AI) molecules via quorum sensing. More recently, AI-3 and the host neuroendocrine (NE) hormones adrenaline and noradrenaline were reported to display cross-talk for the activation of the same signalling pathways. Remarkably, there is increasing evidence to suggest that enteric bacteria sense and respond to the host NE stress hormones adrenaline and noradrenaline to modulate virulence. These responses can be inhibited by α and β-adrenergic receptor antagonists implying a bacterial receptor-based sensing and signalling cascade. In Escherichia coli O157:H7 and Salmonella, QseC has been proposed as the adrenergic receptor. Strikingly, there is an increasing body of evidence that not all the bacterial adrenergic responses require signalling through QseC. Here we provide additional hypotheses to reconcile these observations implicating the existence of alternative adrenergic receptors including BasS, QseE and CpxA and their associated signalling cascades with major roles in interkingdom communication.

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.

Enterohemorrhagic Escherichia coli virulence regulation by two bacterial adrenergic kinases, QseC and QseE

The human pathogen enterohemorrhagic Escherichia coli (EHEC) O157:H7 has two histidine sensor kinases, QseC and QseE, which respond to the mammalian adrenergic hormones epinephrine and norepinephrine by increasing their autophosphorylation. Although QseC and QseE are present in nonpathogenic strains of E. coli, EHEC exploits these kinases for virulence regulation. To further investigate the full extent of epinephrine and its sensors' impact on EHEC virulence, we performed transcriptomic and phenotypic analyses of single and double deletions of qseC and qseE genes in the absence or presence of epinephrine. We showed that in EHEC, epinephrine sensing seems to occur primarily through QseC and QseE. We also observed that QseC and QseE regulate expression of the locus of enterocyte effacement (LEE) genes positively and negatively, respectively. LEE activation, which is required for the formation of the characteristic attaching and effacing (A/E) lesions by EHEC on epithelial cells, is epinephrine dependent. Regulation of the LEE and the non-LEE-contained virulence factor gene nleA by QseE is indirect, through transcription inhibition of the RcsB response regulator. Finally, we show that coincubation of HeLa cells with epinephrine increases EHEC infectivity in a QseC- and QseE-dependent manner. These results genetically and phenotypically map the contributions of the two adrenergic sensors QseC and QseE to EHEC pathogenesis.

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.

Catecholamines increase conjugative gene transfer between enteric bacteria

The ability of pathogenic bacteria to sense and respond to periods of host stress is critical to their lifestyle. Adrenaline and norepinephrine are catecholamines that mediate acute host stress in vertebrates and invertebrates. Catecholamines are also used as environmental cues to enhance growth, motility and virulence of bacterial pathogens via specific binding receptors. Incidence of multidrug resistant and highly virulent bacterial pathogens is on the rise, and majority of the genes for antimicrobial resistance (AMR) and virulence are carried on horizontally transferable genetic elements. Conjugation machinery offers an efficient method for acquisition of AMR and virulence genes, which may be responsible for propelling the evolution of pathogenic bacteria. Here we show that norepinephrine (NE) at physiological concentrations enhances horizontal gene transfer (HGT) efficiencies of a conjugative plasmid from a clinical strain of Salmonella Typhimurium to an Escherichia coli recipient in vitro. Expressions of plasmid encoded transfer (tra) genes necessary for conjugation were also significantly upregulated in the presence of NE. Phentolamine, an α-adrenergic receptor antagonist, negated the effects of NE on conjugation more strongly than propranolol, a β-adrenergic receptor antagonist. This study for the first time provides evidence that innate mediators of acute host stress may influence evolution and adaptation of bacterial pathogens.

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.

Stressor exposure disrupts commensal microbial populations in the intestines and leads to increased colonization by Citrobacter rodentium

The gastrointestinal tract is colonized by an enormous array of microbes that are known to have many beneficial effects on the host. Previous studies have indicated that stressor exposure can disrupt the stability of the intestinal microbiota, but the extent of these changes, as well as the effects on enteric infection, has not been well characterized. In order to examine the ability of stressors to induce changes in the gut microbiota, we exposed mice to a prolonged restraint stressor and then characterized microbial populations in the intestines using both traditional culture techniques and bacterial tag-encoded FLX amplicon pyrosequencing (bTEFAP). Exposure to the stressor led to an overgrowth of facultatively anaerobic microbiota while at the same time significantly reducing microbial richness and diversity in the ceca of stressed mice. Some of these effects could be explained by a stressor-induced reduction in the relative abundance of bacteria in the family Porphyromonadaceae. To determine whether these alterations would lead to increased pathogen colonization, stressed mice, as well as nonstressed controls, were challenged orally with the enteric murine pathogen Citrobacter rodentium. Exposure to the restraint stressor led to a significant increase in C. rodentium colonization over that in nonstressed control mice. The increased colonization was associated with increased tumor necrosis factor alpha (TNF-alpha) gene expression in colonic tissue. Together, these data demonstrate that a prolonged stressor can significantly change the composition of the intestinal microbiota and suggest that this disruption of the microbiota increases susceptibility to an enteric pathogen.

Influence of beta-agonists (ractopamine HCl and zilpaterol HCl) on fecal shedding of Escherichia coli O157:H7 in feedlot cattle

Ractopamine HCl and zilpaterol HCl, beta-agonists recently approved for use in feedlot cattle to improve performance traits and carcass leanness, were examined for their effects on fecal shedding of Escherichia coli O157:H7 in feedlot cattle. Fecal samples (n = 2,454) were obtained from four experiments (one ractopamine HCl, three zilpaterol HCl) over the course of a 3-year period, either by rectal palpation (ractopamine HCl experiment) or from pen-floor fecal pats. Samples were cultured quantitatively and qualitatively for E. coli O157:H7. No significant treatment differences were detected for fecal prevalence of E. coli O157:H7 in the ractopamine HCl experiment. Zilpaterol HCl feeding had no effect (P > 0.20) on fecal shedding in the first or second experiments, with overall E. coli O157:H7 prevalence relatively low (<7%). In the third zilpaterol HCl experiment, the percentage of fecal samples that were E. coli O157:H7 positive following qualitative culture was higher (P < 0.05) in the zilpaterol HCl treatment (10.3%) than for the control (6.1%). The current research showed minimal effects of beta-agonists on fecal shedding of E. coli O157:H7 and indicated that these compounds (fed immediately prior to slaughter) are not a cause for concern from a food safety standpoint.

Norepinephrine represses the expression of toxA and the siderophore genes in Pseudomonas aeruginosa

Among the different extracellular virulence factors produced by Pseudomonas aeruginosa are exotoxin A (ETA) and the pyoverdine and pyochelin siderophores. Production of ETA and the siderophores requires the function of the iron-starvation sigma factor PvdS, the transcriptional activator RegA, and the AraC-activator PchR. Iron represses the production of ETA and the siderophores by repressing the expression of pvdS, regA, and pchR. PvdS regulates the expression of the ETA gene, toxA, regA, and the pyoverdine synthesis genes. The catecholamine norepinephrine enhances the growth of pathogenic bacteria by transferring iron from host-binding proteins. In this study, we elucidated the mechanism by which norepinephrine and other catecholamines induce P. aeruginosa growth. We also investigated whether norepinephrine regulates the expression of toxA and the siderophore genes, and the mechanism of this regulation. Norepinephrine enhanced the growth of P. aeruginosa by supplying iron from transferrin. This provision of iron repressed the expression of toxA, the pyoverdine genes pvdD and pvdE, and their regulators, pvdS, regA, and pchR, suggesting that norepinephrine accomplishes this repression through PvdS and PchR. Additionally, norepinephrine bypassed PvdS and supported the growth of a pvdS deletion mutant, indicating that norepinephrine transfers iron to P. aeruginosa independent of pyoverdine. Thus, norepinephrine apparently influences the pathogenesis of P. aeruginosa by affecting its pattern of growth and the production of virulence factors.

Gram-negative bacterial sensors for eukaryotic signal molecules

Ample evidence exists showing that eukaryotic signal molecules synthesized and released by the host can activate the virulence of opportunistic pathogens. The sensitivity of prokaryotes to host signal molecules requires the presence of bacterial sensors. These prokaryotic sensors, or receptors, have a double function: stereospecific recognition in a complex environment and transduction of the message in order to initiate bacterial physiological modifications. As messengers are generally unable to freely cross the bacterial membrane, they require either the presence of sensors anchored in the membrane or transporters allowing direct recognition inside the bacterial cytoplasm. Since the discovery of quorum sensing, it was established that the production of virulence factors by bacteria is tightly growth-phase regulated. It is now obvious that expression of bacterial virulence is also controlled by detection of the eukaryotic messengers released in the micro-environment as endocrine or neuro-endocrine modulators. In the presence of host physiological stress many eukaryotic factors are released and detected by Gram-negative bacteria which in return rapidly adapt their physiology. For instance, Pseudomonas aeruginosa can bind elements of the host immune system such as interferon-γ and dynorphin and then through quorum sensing circuitry enhance its virulence. Escherichia coli sensitivity to the neurohormones of the catecholamines family appears relayed by a recently identified bacterial adrenergic receptor. In the present review, we will describe the mechanisms by which various eukaryotic signal molecules produced by host may activate Gram-negative bacteria virulence. Particular attention will be paid to Pseudomonas, a genus whose representative species, P. aeruginosa, is a common opportunistic pathogen. The discussion will be particularly focused on the pivotal role played by these new types of pathogen sensors from the sensing to the transduction mechanism involved in virulence factors regulation. Finally, we will discuss the consequence of the impact of host signal molecules on commensally or opportunistic pathogens associated with different human tissue.

The QseC adrenergic signaling cascade in Enterohemorrhagic E. coli (EHEC)

The ability to respond to stress is at the core of an organism's survival. The hormones epinephrine and norepinephrine play a central role in stress responses in mammals, which require the synchronized interaction of the whole neuroendocrine system. Mammalian adrenergic receptors are G-coupled protein receptors (GPCRs); bacteria, however, sense these hormones through histidine sensor kinases (HKs). HKs autophosphorylate in response to signals and transfer this phosphate to response regulators (RRs). Two bacterial adrenergic receptors have been identified in EHEC, QseC and QseE, with QseE being downstream of QseC in this signaling cascade. Here we mapped the QseC signaling cascade in the deadly pathogen enterohemorrhagic E. coli (EHEC), which exploits this signaling system to promote disease. Through QseC, EHEC activates expression of metabolic, virulence and stress response genes, synchronizing the cell response to these stress hormones. Coordination of these responses is achieved by QseC phosphorylating three of the thirty-two EHEC RRs. The QseB RR, which is QseC's cognate RR, activates the flagella regulon which controls bacteria motility and chemotaxis. The QseF RR, which is also phosphorylated by the QseE adrenergic sensor, coordinates expression of virulence genes involved in formation of lesions in the intestinal epithelia by EHEC, and the bacterial SOS stress response. The third RR, KdpE, controls potassium uptake, osmolarity, and also the formation of lesions in the intestine. Adrenergic regulation of bacterial gene expression shares several parallels with mammalian adrenergic signaling having profound effects in the whole organism. Understanding adrenergic regulation of a bacterial cell is a powerful approach for studying the underlying mechanisms of stress and cellular survival.

Bacterial cells respond to the human stress hormones epinephrine (adrenaline) and norepinephrine (noradrenaline). These hormones are sensed by a bacterial receptor named QseC, which is a sensor kinase in the membrane that increases its autophosphorylation upon binding to these host signals. In addition to recognizing these signals, QseC also responds to a bacterial hormone-like molecule named autoinducer-3 (AI-3) that is produced by the human intestinal microbial flora. In this manuscript we have mapped genetically and biochemically the QseC signaling cascade in the deadly pathogen enterohemorrhagic E. coli (EHEC) O157:H7. EHEC uses this signaling system to activate expression of virulence genes. We show that the QseC signaling cascade is very complex so it can precisely modulate when different virulence traits are expressed. Because these sensor kinases are being evaluated as drug targets, a profound understanding of this signaling pathway is important for the development of novel therapeutic strategies to combat bacterial infections.

The neuroendocrine hormone norepinephrine increases Pseudomonas aeruginosa PA14 virulence through the las quorum-sensing pathway

It has been proposed that the gastrointestinal tract environment containing high levels of neuroendocrine hormones is important for gut-derived Pseudomonas aeruginosa infections. In this study, we report that the hormone norepinephrine increases P. aeruginosa PA14 growth, virulence factor production, invasion of HCT-8 epithelial cells, and swimming motility in a concentration-dependent manner. Transcriptome analysis of P. aeruginosa exposed to 500 microM, but not 50 microM, norepinephrine for 7 h showed that genes involved in the regulation of the virulence determinants pyocyanin, elastase, and the Pseudomonas quinolone signal (PQS, 2-heptyl-3-hydroxy-4-quinolone) were upregulated. The production of rhamnolipids, which are also important in P. aeruginosa infections, was not significantly altered in suspension cultures upon exposure to 500 microM norepinephrine but decreased on semisolid surfaces. Swarming motility, a phenotype that is directly influenced by rhamnolipids, was also decreased upon 500 microM norepinephrine exposure. The increase in the transcriptional activation of lasR but not that of rhlR and the increase in the levels of PQS suggest that the effects of norepinephrine are mediated primarily through the las quorum-sensing pathway. Together, our data strongly suggest that norepinephrine can play an important role in gut-derived infections by increasing the pathogenicity of P. aeruginosa PA14.

Adrenaline modulates the global transcriptional profile of Salmonella revealing a role in the antimicrobial peptide and oxidative stress resistance responses

Background

The successful interaction of bacterial pathogens with host tissues requires the sensing of specific chemical and physical cues. The human gut contains a huge number of neurons involved in the secretion and sensing of a class of neuroendocrine hormones called catecholamines. Recently, in Escherichia coli O157:H7, the catecholamines adrenaline and noradrenaline were shown to act synergistically with a bacterial quorum sensing molecule, autoinducer 3 (AI-3), to affect bacterial virulence and motility. We wished to investigate the impact of adrenaline on the biology of Salmonella spp.

Results

We have determined the effect of adrenaline on the transcriptome of the gut pathogen Salmonella enterica serovar Typhimurium. Addition of adrenaline led to an induction of key metal transport systems within 30 minutes of treatment. The oxidative stress responses employing manganese internalisation were also elicited. Cells lacking the key oxidative stress regulator OxyR showed reduced survival in the presence of adrenaline and complete restoration of growth upon addition of manganese. A significant reduction in the expression of the pmrHFIJKLM antimicrobial peptide resistance operon reduced the ability of Salmonella to survive polymyxin B following addition of adrenaline. Notably, both phenotypes were reversed by the addition of the β-adrenergic blocker propranolol. Our data suggest that the BasSR two component signal transduction system is the likely adrenaline sensor mediating the antimicrobial peptide response.

Conclusion

Salmonella are able to sense adrenaline and downregulate the antimicrobial peptide resistance pmr locus through the BasSR two component signalling system. Through iron transport, adrenaline may affect the oxidative stress balance of the cell requiring OxyR for normal growth. Both adrenaline effects can be inhibited by the addition of the β-adrenergic blocker propranolol. Adrenaline sensing may provide an environmental cue for the induction of the Salmonella stress response in anticipation of imminent host-derived oxidative stress. However, adrenaline may also serve in favour of the host defences by lowering antimicrobial peptide resistance and hence documenting for the first time such a function for a hormone.

Temporal regulation of enterohemorrhagic Escherichia coli virulence mediated by autoinducer-2

The autoinducer-2 (AI-2) molecule is produced by many bacterial species, including various human gastrointestinal (GI) tract commensal bacteria, and has been proposed to be involved in interspecies communication. Because pathogens are likely to encounter AI-2 in the GI tract, we studied the effects of AI-2 on various phenotypes associated with enterohemorrhagic Escherichia coli (EHEC) infections. AI-2 attracted EHEC in agarose plug chemotaxis assays and also increased swimming motility, as well as increased EHEC attachment to HeLa cells. The molecular basis underlying the stimulation of EHEC chemotaxis, motility, and colonization by AI-2 was investigated at the transcriptome level using DNA microarrays. We found that exposure to AI-2 altered the expression of 23 locus of enterocyte effacement (LEE) genes directly involved in the production of virulence determinants, as well as other genes associated with virulence (e.g., 46 flagellar/fimbrial genes, 24 iron-related genes), in a temporally defined manner. To our knowledge, this is the first study to report AI-2-mediated regulation of EHEC chemotaxis and colonization, as well as temporal regulation of EHEC transcriptome by AI-2. Our results suggest that AI-2 is an important signal in EHEC infections of the human GI tract.

Inter-kingdom signalling: communication between bacteria and their hosts

Microorganisms and their hosts communicate with each other through an array of hormonal signals. This cross-kingdom cell-to-cell signalling involves small molecules, such as hormones that are produced by eukaryotes and hormone-like chemicals that are produced by bacteria. Cell-to-cell signalling between bacteria, usually referred to as quorum sensing, was initially described as a means by which bacteria achieve signalling in microbial communities to coordinate gene expression within a population. Recent evidence shows, however, that quorum-sensing signalling is not restricted to bacterial cell-to-cell communication, but also allows communication between microorganisms and their hosts.

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.

Effect of norepinephrine on colonisation and systemic spread of Salmonella enterica in infected animals: role of catecholate siderophore precursors and degradation products

Norepinephrine promotes the growth of Salmonella enterica in vitro in iron-restricted conditions imposed by the iron-binding proteins serum transferrin and egg-white ovotransferrin by facilitating the release of bound iron and subsequent uptake by the bacteria. Moreover, significantly increased colonisation and systemic spread were observed in mouse and chicken models of S. enterica infection following pre-treatment of animals with norepinephrine. Both ent and tonB mutants showed no growth promotion by norepinephrine either in liquid medium containing serum or on plates containing hens' egg-white, indicating that the process is dependent both on the ability to synthesise enterobactin and on TonB-dependent uptake of iron. An entS mutant (formerly designated ybdA) and an iroB mutant behaved as wild type in both assays, showing that neither secretion of enterobactin nor conversion of enterobactin to salmochelin S4 is necessary for the effect. On the other hand, the presence of mutations in fes or iroD resulted in loss of growth promotion by norepinephrine in both assays. Since the fes and iroD genes encode enzymes that hydrolyse enterobactin and salmochelin S4 respectively to monomers, these data suggest that excretion of monomeric forms of these siderophores may be important for the uptake of iron released by norepinephrine from transferrin or ovotransferrin. A similar pattern of behaviour was observed with S. enterica serovar Typhimurium in a mouse model of infection; treatment of animals with norepinephrine before intragastric challenge resulted in increased intestinal colonisation and systemic spread of both wild-type and entS mutant strains, while the fes mutant was significantly attenuated in vivo. This suggests that excretion of 2,3-dihydroxybenzoylserine may be essential for norepinephrine-dependent growth promotion in the iron-restricted environment of the infected host. Unlike the situation in vitro, however, tonB mutants of S. enterica serovars Typhimurium and Enteritidis behaved the same as wild type in mouse and chick infection models, respectively, suggesting that norepinephrine-dependent growth stimulation may also occur by TonB-independent uptake of the enterobactin precursor 2,3-dihydroxybenzoic acid.

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.

Catecholamine-induced stimulation of growth in Vibrio species

AIMS

To evaluate the effect of norepinephrine (NE) and related compounds on the growth of bacteria, we have examined the effect of the neuroendocrine hormone NE and related compounds on the growth of Vibrio parahaemolyticus and other human-pathogenic Vibrio species (Vibrio cholerae, Vibrio vulnificus, and Vibrio mimicus).

METHODS AND RESULTS

The effects on bacterial growth were examined using the serum-based medium and viable cells were counted using agar plates. We have shown that NE and its related compounds stimulate growth of V. parahaemolyticus in serum-based medium. This NE-induced growth stimulation was dependent upon the presence of transferrin. NE also stimulated growth of V. mimicus, but not V. cholerae and V. vulnificus.

CONCLUSIONS

These results suggest that the Vibrio species differ in their ability to respond to NE.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is possible that NE and related compounds modulate the pathogenicity of V. parahaemolyticus and V. mimicus.

Influence of exogenous triiodothyronine (T3) on fecal shedding of Escherichia coli O157 in cattle

Fecal prevalence of Escherichia coli O157 in ruminants is highest in the summer months and decreases to low or undetectable levels in the winter. We hypothesize that the seasonal variation of this pathogen is a result of physiological responses within the host animal to changing day length. The thyroid is an endocrine gland known to respond to changing day length. Two experiments were conducted to determine if a hyperthyroid status would initiate fecal shedding of E. coli O157 in cattle during the winter when shedding is virtually nonexistent (winter experiment) or influence cattle actively shedding E. coli O157 (summer experiment). Yearling cattle were group-penned under dry-lot conditions, adjusted to a high concentrate ration, and randomly assigned to treatment: control (1 mL corn oil injected s.c. daily) or triiodothyronine (T(3); 1.5 mg suspended in corn oil injected s.c daily). Cattle were individually processed daily for collection of fecal and blood samples. Treatment with exogenous T(3) produced a significant change in serum thyroid hormone concentrations indicative of a hyperthyroid status in both experiments. No differences (P>0.10) were observed in fecal shedding of E. coli O157 in the winter experiment. In the summer experiment, fecal shedding of E. coli O157 was decreased (P=0.05) by administration of T(3) during the treatment period (days 1-10), tended to be lower (P=0.08) during the following 7-day period of no treatment, and was lower (P=0.01) when examined across the entire experimental period. Results of this research indicate that the thyroid or its hormones may be involved in the seasonal shedding patterns of E. coli O157 in cattle.