Biomedical subjects

Mark Lyte

Publications and source records attributed to Mark Lyte.

At least 19 recordsLinked to original sources

PubMed2007

Specificity of catecholamine-induced growth in Escherichia coli O157:H7, Salmonella enterica and Yersinia enterocolitica.

The present study demonstrates that catecholamine responsiveness in Yersinia enterocolitica, a bacterial pathogen whose infectious spectrum is principally limited to the gut, is limited to norepinephrine and dopamine, and not epinephrine; this behavior contrasts with observations for two pathogens with a wider extra-gastrointestinal spectrum, Escherichia coli O157:H7 and Salmonella enterica, which respond to all three catecholamines. Epinephrine showed lower potency than norepinephrine and dopamine in inducing growth of E. coli and S. enterica, and was a potent antagonist of norepinephrine and dopamine growth responsiveness in Y. enterocolitica. Given that only norepinephrine and dopamine and not epinephrine-containing neurons are found with the enteric nervous system, the results suggest that certain of the more exclusive enteric pathogens may have developed response systems preferentially for those neuroendocrine hormones that are produced by the enteric nervous system as host-derived signals by which to sense the environment and initiate pathogenic processes.

Bacteriological Techniques↗

PubMed2006

Induction of anxiety-like behavior in mice during the initial stages of infection with the agent of murine colonic hyperplasia Citrobacter rodentium.

Symptoms of anxiety frequently occur concomitant to the development and persistence of inflammatory bowel disease (IBD) in patients. In the present study, we utilized an animal model of IBD, infection with Citrobacter rodentium, to determine whether the infection per se can drive anxiety-like behavior. Nine-week-old CF-1 male mice were challenged orally with either saline or C. rodentium. Early in the infective process (7-8 h later), mice were tested on a hole-board open field apparatus for anxiety-like behavior measurement. Immediately following behavioral testing, plasma samples were obtained for immune cytokine analysis and colons were excised for histological analysis. In additional animals, vagal ganglia were removed and processed for c-Fos protein detection. Challenge with C. rodentium significantly increased anxiety-like behavior as evidenced by avoidance of the center area and increased risk assessment behavior. Plasma levels of the cytokines IFN-gamma, TNF-alpha and IL-12 were not different. However vagal sensory ganglia from C. rodentium-treated animals evinced significantly more c-Fos protein-positive neurons, consistent with vagal afferent transmission of C. rodentium-related signals from gut to brain. Histological examination of the colon indicated a lack of overt inflammation at the 8 h post-challenge time point, indicating that the differences in behavior were unlikely to follow from inflammation-related stress. The results of the present study demonstrate that infection with C. rodentium can induce anxiety-like symptoms that are likely mediated via vagal sensory neurons.

Administration, Oral↗

PubMed2006

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

The sympathetic neurotransmitter norepinephrine has been found to increase mucosal adherence of enterohemorrhagic Escherichia coli O157:H7 in explants of murine cecum and porcine distal colon. In the present study, we tested the hypothesis that norepinephrine augments the initial, loose adherence of this important pathogen to the intestinal mucosa. In mucosal sheets of porcine cecum or proximal, spiral and distal colon mounted in Ussing chambers, norepinephrine (10 microM, contraluminal addition) increased mucosal adherence of wild-type E. coli O157:H7 strain 85-170; in the cecal mucosa, this effect occurred within 30-90 min after bacterial inoculation. In addition, norepinephrine transiently increased short-circuit current in cecal and colonic mucosal sheets, a measure of active anion transport. Norepinephrine was effective in promoting cecal adherence of a non-O157 E. coli strain as well as E. coli O157:H7 eae or espA mutant strains that are incapable of intimate mucosal attachment. Nerve fibers immunoreactive for the norepinephrine synthetic enzyme dopamine beta-hydroxylase appeared in close proximity to the cecal epithelium, and the norepinephrine reuptake blocker cocaine, like norepinephrine and the selective alpha2-adrenoceptor agonist UK-14,304, increased E. coli O157:H7 adherence. These results suggest that norepinephrine, acting upon the large bowel mucosa, modulates early, non-intimate adherence of E. coli O157:H7 and probably other mucosa-associated bacteria. Sympathetic nerves innervating the cecocolonic mucosa may link acute stress exposure or psychostimulant abuse with an increased microbial colonization of the intestinal surface. This in turn may alter host susceptibility to enteric infections.

Adhesins, Bacterial↗

PubMed2006

Enhancement of in vitro growth of pathogenic bacteria by norepinephrine: importance of inoculum density and role of transferrin.

Norepinephrine is a stress hormone that enhances bacterial growth. We examined the effects of a small inoculum on the norepinephrine-induced growth of species previously reported to be unaffected by norepinephrine. The results indicated that a reduced inoculum density is essential for observing norepinephrine-induced effects. Additional studies using serum-free media suggested that transferrin plays a role in norepinephrine-induced growth.

Colony Count, Microbial↗

PubMed2005

Activation in vagal afferents and central autonomic pathways: early responses to intestinal infection with Campylobacter jejuni.

Abundant evidence now supports the idea that multiple pathways or mechanisms underlie communication from the immune system to the brain. The presence of a variety of mechanisms suggests that they may each contribute something different to immunosensory signaling. For instance, brain mediated immune signal transduction is dependent upon the presence of circulating mediators whereas peripheral sensory nerves are more likely to be important early on in an infection, prior to elevation of circulating cytokines, or in local infections within the terminal fields of these nerves. To test the hypothesis that local infection in the gut activates vagal sensory neurons, we assessed expression of the neuronal activation marker c-Fos in neurons in the vagal sensory ganglia and in the primary sensory relay nucleus for the vagus, the nucleus of the solitary tract (nTS) in mice treated orally either with saline or live Campylobacter jejuni (C. jejuni). Male CF1 mice were inoculated orally with either C. jejuni or saline, and c-Fos expression in the vagal sensory neurons and brain 4-12 h later was assessed via immunohistochemistry. Oral inoculation with C. jejuni led to a significant increase in c-Fos expression in neurons bilaterally in the vagal ganglia, in the absence of elevated levels of circulating pro-inflammatory cytokines. C. jejuni treatment activated neurons in the nTS, as well as in brain regions associated with primary viscerosensory pathways and the central autonomic network. These findings provide evidence that peripheral sensory neurons contribute an early signal to the brain regarding potential pathogens.

Animals↗

PubMed2005

Recommended housing conditions and test procedures can interact to obscure a significant experimental effect.

Routine animal husbandry variables, such as group housing of mice and the order of testing of cage-mates, are currently viewed to be essentially neutral with respect to the outcome of most, if not all, animal-based experiments, including those that utilize behavioral measurements. During the course of experiments that have utilized the elevated plus-maze to examine the ability of a bacterial challenge of mice to induce anxiety-like behavior, due to the activation of various cytokine pathways, we followed the recommendation of laboratory animal care staff to house the mice in pairs. Whenwe testedthe members of the pairs successively, it was found, for the first experimental set, that the behavior that reflects anxiety (time in closed arms) of the first-tested animal differed from that of the second-tested animal for both the experimental and the control animals and, critically, that these changes were in the opposite directions for the controls and the experimental animals, thus obscuring the effect of the experimental manipulation. A second, independent experimental set also obtained a significant effect for the order of testing effect in the bacterial-challenged group, but not in the saline control group, although a similar trend was evident in this group as well. These results indicate that special care should to be taken in implementing housing recommendations and that preliminary tests may be necessary to ensure that housing conditions do not interact with tests of the phenomenon under experimental investigation.

Animals↗

PubMed2004

Brain response to cecal infection with Campylobacter jejuni: analysis with Fos immunohistochemistry.

Infections with bacterial pathogens can induce increased anxiety-like behaviors in rodents without otherwise noticeable behavioral or physiological symptoms of sickness, as shown with the food-borne pathogen Campylobacter jejuni. This observation implicates the ability of the brain to sense, and respond to, such an infection. We tested our hypothesis that intestinal infection with the gram-negative bacterium C. jejuni leads to activation of certain brain regions that process gastro-intestinal sensory information. The induction of c-Fos protein as a marker for neuronal activation was assessed in the brains of mice inoculated orally with live C. jejuni, as compared to saline-treated controls. Upon colonization of the intestines, C. jejuni activated visceral sensory nuclei in the brainstem (the nucleus of the solitary tract and the lateral parabrachial nucleus) both one and two days after the oral challenge. In addition, increased c-Fos expression occurred in the hypothalamic paraventricular nucleus on the second day. This neural response occurred in the absence of measurable systemic immune activation, as serum levels of tumor necrosis factor-alpha, interleukin-1beta, and interleukin-6 were undetectable and/or unchanged. These findings support the notion that information about infection with C. jejuni in the gut is indeed relayed to the visceral sensory structures in the brain. The brain responses observed could contribute to changes in behavior observed after infection.

Analysis of Variance↗

PubMed2004

Microbial endocrinology and infectious disease in the 21st century.

More than 70 years ago, a new age in endocrinology was just beginning with the first purification of a hormone, adrenaline. As early as 1930, almost immediately following its first use, cases of adrenaline-associated sepsis were reported. From this time, there have been reports associating the elaboration of neuroendocrine hormones, such as adrenaline, with infectious disease. The most widely accepted theory to explain the ability of hormones to influence the course of infection involves the suppression of the immune system. The theory that the infectious microorganism itself might be equally responsive to the host's neuroendocrine environment has not been considered. It is the intent of this article to introduce a new perspective to the current understanding of the factors that mediate the ability of bacteria to cause disease, and to demonstrate that neuroendocrinology and microbiology intersect to form the interdisciplinary field of microbial endocrinology.

Bacteria↗

PubMed2004

The neuroendocrine stress hormone norepinephrine augments Escherichia coli O157:H7-induced enteritis and adherence in a bovine ligated ileal loop model of infection.

The role of the neuroendocrine environment in the pathogenesis of enteric bacterial infections is increasingly being recognized. Here we report that norepinephrine augments Escherichia coli O157:H7-induced intestinal inflammatory and secretory responses as well as bacterial adherence to intestinal mucosa in a bovine ligated ileal loop model of infection. Norepinephrine modulation of enteritis and adherence was dependent on the ability of E. coli O157:H7 to form attaching and effacing lesions.

Animals↗

PubMed2004

Adrenergic modulation of Escherichia coli O157:H7 adherence to the colonic mucosa.

Enteric neurotransmitters can modulate the biodefensive functions of the intestinal mucosa, but their role in mucosal interactions with enteropathogens is not well defined. Here we tested the hypothesis that norepinephrine (NE) modulates interactions between enterohemorrhagic Escherichia coli O157:H7 (EHEC) and the colonic epithelium. Mucosal sheets from porcine distal colon were mounted in Ussing chambers. Drugs and an inoculum of either Shiga toxin-negative or -positive EHEC were added to the contraluminal and luminal bathing medium, respectively. After 90 min, adherent bacteria were quantified by an adherence assay and by immunohistochemical methods; short-circuit current (I(sc)) was measured continuously to assess changes in active ion transport. NE-treated tissues exhibited concentration-dependent increases in I(sc) and EHEC adherence. NE did not alter adherence of a rodent-adapted, noninfectious E. coli strain or two porcine-adapted non-O157 E. coli strains. The actions of NE on EHEC adherence but not I(sc) were prevented by the alpha-adrenergic antagonist yohimbine and the PKA activator Sp-8-bromoadenosine-3',5'-cyclic monophosphorothioate. Like NE, the PKA inhibitor Rp-8-bromoadenosine-3',5'-cyclic monophosphorothioate or indirectly acting sympathomimetic agents increased EHEC adherence. Nerve fibers immunoreactive for the NE-synthesizing enzymes tyrosine hydroxylase and dopamine beta-hydroxylase appeared to innervate the colonic epithelium. EHEC-like immunoreactivity on the colonic surface had the appearance of bacterial microcolonies and increased after NE treatment by a phentolamine-sensitive mechanism. Through interactions with alpha(2)-adrenergic receptors, NE appears to increase EHEC adherence to the colonic mucosa. Changes in sympathetic neural outflow may alter intestinal susceptibility to infection.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed2004

The biogenic amine tyramine modulates the adherence of Escherichia coli O157:H7 to intestinal mucosa.

The environmental factors that influence the ability of Escherichia coli O157:H7 to attach to the intestinal mucosa are incompletely understood. In the present study, the ability of one of the most common biogenic amines present in food, tyramine, to influence the ability of E. coli O157:H7 to adhere to murine cecal mucosa was examined. Ex vivo full-thickness sheets of murine cecum were mounted in Ussing chambers, which preserved the enteric nervous system innervation of the luminal epithelia and thereby allowed us to achieve a closer approximation of bacterial adherence than would be encountered in vivo. After exposure of the luminal aspect of the cecum to tyramine, E. coli O157:H7 was added for 90 min. The cecal tissue was then removed and washed, and adhered E. coli O157:H7 was enumerated using a selective medium. Tyramine significantly increased E. coli O157:H7 adherence to cecal mucosa when compared to that of controls. The 50% effective concentration of tyramine was 92.6 microM. Specific adrenergic antagonists were then employed to examine whether the effect of tyramine was mediated through alpha- or beta-adrenergic receptors on the intestinal tissue. Pretreatment of tissues with either the alpha-adrenergic receptor antagonist phentolamine or the beta-adrenergic receptor antagonist propranolol prevented the action of tyramine. Measurement of active transepithelial ion transport and ionic permeability in the cecal sheets before and after the addition of tyramine and E. coli O157:H7 did not show any impairment of tissue viability or transepithelial conductance. Further, tyramine did not influence either the growth of E. coli O157:H7 or the expression of the intimin attachment factor. The present findings suggest that biogenic amines, such as tyramine, present within the food matrix influence host susceptibility to E. coli O157:H7 infection.

Animals↗

PubMed2003

Involvement of enterobactin in norepinephrine-mediated iron supply from transferrin to enterohaemorrhagic Escherichia coli.

Exposure of bacteria to members of the stress-associated family of catecholamine hormones, principally norepinephrine, has been demonstrated to increase both growth and production of virulence-related factors. Mutation of genes for enterobactin synthesis and uptake revealed an absolute requirement for enterobactin in norepinephrine-stimulated growth of Escherichia coli O157:H7. The autoinducer produced by norepinephrine-stimulated E. coli could not substitute for enterobactin. We also demonstrate that norepinephrine promotes iron shuttling between transferrin molecules, thereby enabling the bacterial siderophore enterobactin to more readily acquire iron for growth. These results suggest one of the possible mechanisms by which the hormonal output of stress may affect enterohaemorrhagic E. coli pathogenicity.

Enterobactin↗

PubMed2003

Stimulation of Staphylococcus epidermidis growth and biofilm formation by catecholamine inotropes.

BACKGROUND: Bacterial colonisation of indwelling medical devices by coagulase-negative staphylococci is a prevalent risk in intensive-care units. Factors determining biofilm formation and progression to catheter- related infection are incompletely understood. We postulated that administration of inotropic agents via indwelling intravenous catheters may stimulate growth and formation of biofilms by Staphylococcus epidermidis. METHODS: Inocula representing physiologically relevant infecting doses of S epidermidis were incubated in a minimum medium supplemented with fresh human plasma in the presence or absence of pharmacological concentrations of norepinephrine or dobutamine. Biofilm formation on polystyrene and medical-grade silicone was examined. After incubation, cultures were assessed for growth and formation of biofilms by colony counting and scanning electronmicroscopy. The production of exopolysaccharide, a major constituent of S epidermidis biofilms, was also assessed by use of immunofluorescence microscopy. FINDINGS: Incubation of S epidermidis with catecholamine inotropes in the presence of human plasma resulted in a significant increase in growth compared with control on both polystyrene and silicone surfaces, with pronounced increases in biofilm formation as visualised by scanning electronmicroscopy. Experiments with transferrin labelled with radioactive iron showed the ability of catecholamine inotropes to facilitate acquisition of iron by S epidermidis. Immunofluorescence microscopy revealed extensive exopolysaccharide production associated with S epidermidis biofilms. INTERPRETATION: The ability of catecholamine inotropic drugs to stimulate bacterial proliferation and biofilm formation may be an aetiological factor in the development of intravascular catheter colonisation and catheter-related infection. The removal of iron from transferrin for subsequent use by S epidermidis is a possible mechanism by which catecholamine inotropes stimulate bacterial growth as biofilms.

Adult↗

PubMed2003

Neuromodulation of enteropathogen internalization in Peyer's patches from porcine jejunum.

Jejunal Peyer's patches (JPP) are innervated sites of immune induction and enteropathogen infection. We investigated the role of enteric nerves in modulating pathogen entry into porcine JPP. Presumptive norepinephrine (NE)-containing nerve fibers were localized in JPP domes and follicle-associated villi by secondary immunofluorescence histochemistry. NE or the neuronal conduction blocker saxitoxin increased intracellular internalization of pathogenic Salmonella choleraesuis and Escherichia coli O157:H7, but not nonpathogenic E. coli, into isolated JPP mucosa. NE action was prevented by the alpha-adrenergic antagonist phentolamine. Withdrawal of enteric neural activity or NE administration appears to modulate JPP interactions with pathogenic bacteria.

Animals↗

PubMed2003

Catecholamines modulate Escherichia coli O157:H7 adherence to murine cecal mucosa.

Enterohemorrhagic Escherichia coli O157:H7 (EHEC) is an important food-borne pathogen. While the molecular mechanisms governing E. coli O157:H7 pathogenesis have been intensively investigated, the role of host factors has received less attention. In this study, we tested the hypothesis that the enteric catecholamines norepinephrine (NE) and dopamine (DA) modulate interactions of the cecal mucosa with E. coli O157:H7. Full-thickness sheets of murine cecum were mounted in Ussing chambers and short circuit current and tissue electrical conductance were periodically determined to assess active transepithelial ion transport and ionic permeability, respectively. Neurochemicals and stationary-phase E. coli O157:H7 were exposed respectively to the contraluminal and luminal aspects of the mucosa. Epithelial adherence of E. coli O157:H7 was quantified by a bacterial adhesion assay after 90 min of luminal E. coli O157:H7 exposure. DA and NE increased E. coli O157:H7 adherence relative to untreated control tissues at 50% effective concentrations of 3.8 microM and 4.2 microM respectively. Pretreatment of tissues with either the alpha-adrenergic antagonist phentolamine or the beta-adrenergic antagonist propranolol prevented the action of NE. The effect of DA was prevented by the dopamine antagonist haloperidol. The drugs did not impair tissue viability or transepithelial conductance. The present findings suggest that enteric catecholamines modulate E. coli O157:H7 adherence to the cecal epithelium. Conditions associated with elevated catecholamine release, such as stress exposure, may influence host susceptibility to E. coli O157:H7 infection.

Animals↗

PubMed2002

Systemic and pulmonary effector cell function after injury.

OBJECTIVE: Traumatic injury initiates a complex inflammatory response that is associated with end-organ dysfunction, immunosuppression, and the development of nosocomial infection. We hypothesize that the lungs of injured patients experience a unique inflammatory response to traumatic injury in which the ability of alveolar effector cells to respond to a bacterial challenge is impaired. DESIGN: Prospective, longitudinal comparative study. SETTING: The surgical intensive care unit of an ACS level I trauma center. PATIENTS: Forty consecutive multiple trauma patients requiring mechanical ventilation. MEASUREMENT: Blood and bronchoalveolar lavage fluid were collected on admission, 24, and 48 hrs postinjury. Interleukin (IL)-6, IL-8, and IL-10 were measured in each sample initially and after lipopolysaccharide stimulation by using an ex vivo model of whole blood and bronchoalveolar lavage fluid cellular contents. Five patients who underwent elective surgery formed a control group. MAIN RESULTS: Systemic and alveolar levels of IL-6, IL-8, and IL-10 increase dramatically after severe injury. Levels of IL-6 and IL-8 in trauma bronchoalveolar lavage fluid are significantly greater than those of the systemic circulation. Whereas whole blood up-regulates production of IL-6 and IL-8 in response to lipopolysaccharide, bronchoalveolar lavage fluid cellular contents do not. In contrast, bronchoalveolar lavage fluid and whole blood from injured patients contain similar amounts of IL-10 and both up-regulate IL-10 production in response to lipopolysaccharide. CONCLUSION: The lungs of injured patients experience a profound proinflammatory response to injury more severe than that of the systemic circulation. Within this setting, the ability of alveolar effector cells to respond to a bacterial challenge is diminished compared with that of systemic cells. As such, alveolar effector cell function after injury seems to be impaired, possibly explaining the high frequency of pulmonary infection among these patients.

Adult↗

PubMed2002

Increased IL-10 production and HLA-DR suppression in the lungs of injured patients precede the development of nosocomial pneumonia.

The incidence of nosocomial pneumonia (NP) among injured patients is substantial. We hypothesize that traumatic injury induces alterations in local organ effector cell function that may predispose the lungs of injured patients to infection. It is the objective of this study to compare the systemic and alveolar effector cell response to injury and assess the relationship these have to the development of NP. Peripheral blood and bronchoalveolar lavage fluid (BAL) were collected from 10 elective surgery patients (controls) and 16 multitrauma patients at 12, 36, and 60 h post-injury. Systemic and alveolar levels of IL-8 and IL-10 were measured. CD11b expression on peripheral blood neutrophils (PBN) and alveolar neutrophils (AN) and HLA-DR expression on peripheral blood monocytes (PBM) and alveolar macrophages (AM) were measured. Alveolar levels of IL-8 and IL-10 were significantly higher than systemic levels after injury. HLA-DR expression was reduced on both PBM and AM after injury but was lowest on the AM. Six of 16 patients (38%) developed NP (NP+). There were no differences in cytokine levels (IL-8 and IL-10) or effector cell phenotype (CD11b and HLA-DR expression) within the systemic circulation of NP+ and NP- patients. In contrast, NP+ and NP- patients differed significantly in alveolar cytokine levels and alveolar effector cell phenotype. IL-8 was significantly higher in BAL form NP+ patients at all time points after injury. Furthermore, alveolar levels of IL-10 decreased in NP- patients but increased in NP+ patients. In all patients, AM HLA-DR expression was significantly reduced from normal controls 12 h post-injury. In NP-patients, AM HLA-DR expression returned to normal 60 h post-injury, whereas in NP+ patients, expression remained suppressed. These findings identify distinct trends in local organ cytokine production and alterations in effector cell phenotype that precede NP. The persistence of reduced HLA-DR expression amidst increasing levels of IL-10 in NP+ patients suggest that cell-mediated immune function is being suppressed. As such, local organ immunosuppression may be responsible for the development of nosocomial pneumonia in injured patients.

Adult↗

PubMed2002

Epinephrine as a mediator of pulmonary neutrophil sequestration.

Neutrophil-mediated lung injury is a potential complication of trauma and sepsis. Concomitant with trauma and sepsis, there is an immediate and sustained systemic elevation of catecholamines including epinephrine. In the absence of trauma or sepsis, we examined whether epinephrine contributes to the accumulation of neutrophils in the lung. Eight- to 12-week-old male CF-1 mice were injected i.p. with 0.2 mL of normal saline or epinephrine (0.1-5.0 mg/kg). An unmanipulated control group was included to examine the stress of i.p. injection. Animals were sacrificed at predetermined time points, and lung and spleen were harvested. PMN accumulation was assessed by using a myeloperoxidase (MPO) assay, which is an indirect marker for neutrophil presence. Morphometric analysis of lung tissue was performed by a pathologist blinded to the groups. Increasing epinephrine doses resulted in a significantly increased accumulation of pulmonary neutrophils compared with normal saline. The stress of normal saline injection also resulted in a significantly greater pulmonary neutrophil accumulation than unmanipulated controls. The effects of epinephrine on pulmonary neutrophil accumulation were greatest at 2 h, but they were not significantly different from saline-injected controls by 12 h. These results correlated with histological analysis. There were no significant differences in spleen MPO activity between groups, suggesting an organ-specific mechanism of epinephrine-induced pulmonary neutrophil sequestration. In the absence of trauma, shock, or infection, epinephrine results in the accumulation of neutrophils in murine lungs. The finding that "injection stress" increased lung neutrophil sequestration suggests the possibility that this mechanism may be physiologically relevant. Thus, epinephrine release in trauma may set the stage for development of neutrophil-mediated acute lung injury.

Animals↗