Stress and intestinal microflora

Microbiology of human spaceflight: microbial responses to mechanical forces that impact health and habitat sustainability

SUMMARYUnderstanding the dynamic adaptive plasticity of microorganisms has been advanced by studying their responses to extreme environments. Spaceflight research platforms provide a unique opportunity to study microbial characteristics in new extreme adaptational modes, including sustained exposure to reduced forces of gravity and associated low fluid shear force conditions. Under these conditions, unexpected microbial responses occur, including alterations in virulence, antibiotic and stress resistance, biofilm formation, metabolism, motility, and gene expression, which are not observed using conventional experimental approaches. Here, we review biological and physical mechanisms that regulate microbial responses to spaceflight and spaceflight analog environments from both the microbe and host-microbe perspective that are relevant to human health and habitat sustainability. We highlight instrumentation and technology used in spaceflight microbiology experiments, their limitations, and advances necessary to enable next-generation research. As spaceflight experiments are relatively rare, we discuss ground-based analogs that mimic aspects of microbial responses to reduced gravity in spaceflight, including those that reduce mechanical forces of fluid flow over cell surfaces which also simulate conditions encountered by microorganisms during their terrestrial lifecycles. As spaceflight mission durations increase with traditional astronauts and commercial space programs send civilian crews with underlying health conditions, microorganisms will continue to play increasingly critical roles in health and habitat sustainability, thus defining a new dimension of occupational health. The ability of microorganisms to adapt, survive, and evolve in the spaceflight environment is important for future human space endeavors and provides opportunities for innovative biological and technological advances to benefit life on Earth.

The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective

The physiological consequences of stress often manifest in the gastrointestinal tract. Traumatic or chronic stress is associated with widespread maladaptive changes throughout the gut, although comparatively little is known about the effects of acute stress. Furthermore, these stress-induced changes in the gut may increase susceptibility to gastrointestinal disorders and infection, and impact critical features of the neural and behavioural consequences of the stress response by impairing gut-brain axis communication. Understanding the mechanisms behind changes in enteric nervous system circuitry, visceral sensitivity, gut barrier function, permeability, and the gut microbiota following stress is an important research objective with pathophysiological implications in both neurogastroenterology and psychiatry. Moreover, the gut microbiota has emerged as a key aspect of physiology sensitive to the effects of stress. In this review, we focus on different aspects of the gastrointestinal tract including gut barrier function as well as the immune, humoral and neuronal elements involved in gut-brain communication. Furthermore, we discuss the evidence for a role of stress in gastrointestinal disorders. Existing gaps in the current literature are highlighted, and possible avenues for future research with an integrated physiological perspective have been suggested. A more complete understanding of the spatial and temporal dynamics of the integrated host and microbial response to different kinds of stressors in the gastrointestinal tract will enable full exploitation of the diagnostic and therapeutic potential in the fast-evolving field of host-microbiome interactions.

The Use of Gut Microbial Modulation Strategies as Interventional Strategies for Ageing

Gut microbial composition codevelops with the host from birth and is influenced by several factors, including drug use, radiation, psychological stress, dietary changes and physical stress. Importantly, gut microbial dysbiosis has been clearly associated with several diseases, including cancer, rheumatoid arthritis and Clostridium difficile-associated diarrhoea, and is known to affect human health and performance. Herein, we discuss that a shift in the gut microbiota with age and reversal of age-related modulation of the gut microbiota could be a major contributor to the incidence of numerous age-related diseases or overall human performance. In addition, it is suggested that the gut microbiome of long-lived animals such as reptiles should be investigated for their unique properties and contribution to the potent defense system of these species could be extrapolated for the benefit of human health. A range of techniques can be used to modulate the gut microbiota to have higher abundance of “beneficial” microbes that have been linked with health and longevity.

Humans as Superorganisms: How Microbes, Viruses, Imprinted Genes, and Other Selfish Entities Shape Our Behavior

Psychologists and psychiatrists tend to be little aware that (a) microbes in our brains and guts are capable of altering our behavior; (b) viral DNA that was incorporated into our DNA millions of years ago is implicated in mental disorders; (c) many of us carry the cells of another human in our brains; and (d) under the regulation of viruslike elements, the paternally inherited and maternally inherited copies of some genes compete for domination in the offspring, on whom they have opposite physical and behavioral effects. This article provides a broad overview, aimed at a wide readership, of the consequences of our coexistence with these selfish entities. The overarching message is that we are not unitary individuals but superorganisms, built out of both human and nonhuman elements; it is their interaction that determines who we are.

Psychological Stress, Immunity, and the Effects on Indigenous Microflora

Psychological stress is an intrinsic part of life that affects all organs of the body through direct nervous system innervation and the release of neuroendocrine hormones. The field of PsychoNeuroImmunology (PNI) has clearly demonstrated that the physiological response to psychological stressors can dramatically impact the functioning of the immune system, thus identifying one way in which susceptibility to or severity of diseases are exacerbated during stressful periods. This chapter describes research at the interface between the fields of PNI and Microbial Endocrinology to demonstrate that natural barrier defenses, such as those provided by the commensal microflora, can be disrupted by exposure to psychological stressors. These stress effects are evident in the development of the intestinal microflora in animals born from stressful pregnancy conditions, and in older animals with fully developed microbial populations. Moreover, data are presented demonstrating that exposure to different types of stressors results in the translocation of microflora from cutaneous and mucosal surfaces into regional lymph nodes. When considered together, a scenario emerges in which psychological stressors induce a neuroendocrine response that has the potential to directly or indirectly affect commensal microflora populations, the integrity of barrier defenses, and the internalization of microbes. Finally, a hypothesis is put forth in which stressor-induced alterations of the microflora contribute to the observed stressor-induced increases in inflammatory markers in the absence of overt infection.

Gut microbiota regulates key modulators of social behavior

Social behavior plays a pivotal role in the mental well-being of an individual. Continuous efforts in the past have led to advancements in the area of how the brain regulates emotion and cognition, while the understanding of human social behavior still remains eluded. A major breakthrough in understanding the etiology of neurological disorders is the recent insight on the role of the gut microbiota (GM). Human GM also referred to as the "forgotten organ" is home to 10(13-14) microorganisms, which is 10 times the number of cells present in the human body. In addition, the gut microbiome (total genome of GM) is 150 times greater as compared to the human genome. An emerging concept gaining worldwide focus and acceptance is that, this much big genome can potentially control human behavior and other biological functions. Herein we hypothesize on the basis of GM's ability to modify brain and behavior and that it can directly or indirectly control social behavior. This review focuses on the association of GM with various domains of social behavior like stress, cognition and anxiety.

Influence of stressor-induced nervous system activation on the intestinal microbiota and the importance for immunomodulation

The body is colonized by a vast population of genetically diverse microbes, the majority of which reside within the intestines to comprise the intestinal microbiota. During periods of homeostasis, these microbes reside within stable climax communities, but exposure to physical, physiological, as well as psychological stressors can significantly impact the structure of the intestinal microbiota. This has been demonstrated in humans and laboratory animals, with the most consistent finding being a reduction in the abundance of bacteria in the genus Lactobacillus. Whether stressor exposure also changes the function of the microbiota, has not been as highly studied. The studies presented in this review suggest that stressor-induced disruption of the intestinal microbiota leads to increased susceptibility to enteric infection and overproduction of inflammatory mediators that can induce behavioral abnormalities, such as anxiety-like behavior. Studies involving germfree mice also demonstrate that the microbiota are necessary for stressor-induced increases in innate immunity to occur. Exposing mice to a social stressor enhances splenic macrophage microbicidal activity, but this effect fails to occur in germfree mice. These studies suggest a paradigm in which stressor exposure alters homeostatic interactions between the intestinal microbiota and mucosal immune system and leads to the translocation of pathogenic, and/or commensal, microbes from the lumen of the intestines to the interior of the body where they trigger systemic inflammatory responses and anxiety-like behavior. Restoring homeostasis in the intestines, either by removing the microbiota or by administering probiotic microorganisms, can ameliorate the stressor effects.

Effects of the modulation of microbiota on the gastrointestinal immune system and bowel function

The gastrointestinal tract harbors a tremendous number and variety of commensal microbiota. The intestinal mucosa simultaneously absorbs essential nutrients and protects against detrimental antigens or pathogenic microbiota as the first line of defense. Beneficial interactions between the host and microbiota are key requirements for host health. Although the gut microbiota has been previously studied in the context of inflammatory diseases, it has recently become clear that this microbial environment has a beneficial role during normal homeostasis, by modulating the immune system or bowel motor function. Recent studies revealed that microbiota, including their metabolites, modulate key signaling pathways involved in the inflammation of the mucosa or the neurotransmitter system in the gut-brain axis. The underlying molecular mechanisms of host-microbiota interactions are still unclear; however, manipulation of microbiota by probiotics or prebiotics is becoming increasingly recognized as an important therapeutic option, especially for the treatment of the dysfunction or inflammation of the intestinal tract.

The contributing role of the intestinal microbiota in stressor-induced increases in susceptibility to enteric infection and systemic immunomodulation

The body is colonized by highly complex and genetically diverse communities of microbes, the majority of which reside within the intestines in largely stable but dynamically interactive climax communities. These microbes, referred to as the microbiota, have many functions that enhance the health of the host, and it is now recognized that the microbiota influence both mucosal and systemic immunity. The studies outlined in this review demonstrate that the microbiota are also involved in stressor-induced immunomodulation. Exposure to different types of stressors, including both physical and psychological stressors, changes the composition of the intestinal microbiota. The altered profile increases susceptibility to an enteric pathogen, i.e., Citrobacter rodentium, upon oral challenge, but is also associated with stressor-induced increases in innate immune activity. Studies using germfree mice, as well as antibiotic-treated mice, provide further evidence that the microbiota contribute to stressor-induced immunomodulation; stressor-induced increases in splenic macrophage microbicidal activity fail to occur in mice with no, or reduced, intestinal microbiota. While the mechanisms by which microbiota can impact mucosal immunity have been studied, how the microbiota impact systemic immune responses is not clear. A mechanism is proposed in which stressor-induced degranulation of mucosal mast cells increases the permeability of the intestines. This increased permeability would allow intact bacteria and/or bacterial products (like peptidoglycan) to translocate from the lumen of the intestines to the interior of the body, where they directly, or indirectly, prime the innate immune system for enhanced reactivity to antigenic stimulation.

Exposure to a social stressor alters the structure of the intestinal microbiota: implications for stressor-induced immunomodulation

The bodies of most animals are populated by highly complex and genetically diverse communities of microorganisms. The majority of these microbes reside within the intestines in largely stable but dynamically interactive climax communities that positively interact with their host. Studies from this laboratory have shown that stressor exposure impacts the stability of the microbiota and leads to bacterial translocation. The biological importance of these alterations, however, is not well understood. To determine whether the microbiome contributes to stressor-induced immunoenhancement, mice were exposed to a social stressor called social disruption (SDR), that increases circulating cytokines and primes the innate immune system for enhanced reactivity. Bacterial populations in the cecum were characterized using bacterial tag-encoded FLX amplicon pyrosequencing. Stressor exposure significantly changed the community structure of the microbiota, particularly when the microbiota were assessed immediately after stressor exposure. Most notably, stressor exposure decreased the relative abundance of bacteria in the genus Bacteroides, while increasing the relative abundance of bacteria in the genus Clostridium. The stressor also increased circulating levels of IL-6 and MCP-1, which were significantly correlated with stressor-induced changes to three bacterial genera (i.e., Coprococcus, Pseudobutyrivibrio, and Dorea). In follow up experiments, mice were treated with an antibiotic cocktail to determine whether reducing the microbiota would abrogate the stressor-induced increases in circulating cytokines. Exposure to SDR failed to increase IL-6 and MCP-1 in the antibiotic treated mice. These data show that exposure to SDR significantly affects bacterial populations in the intestines, and remarkably also suggest that the microbiota are necessary for stressor-induced increases in circulating cytokines.

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.

The occurrence of antimicrobial resistance and class 1 integrons among commensal Escherichia coli isolates from infants and elderly persons

Background

The aim of our study was to compare the presence of the intI1 gene and its associations with the antibiotic resistance of commensal Escherichia coli strains in children with/without previous antibiotic treatments and elderly hospitalized/healthy individuals.

Methods

One-hundred-and-fifteen intestinal E. coli strains were analyzed: 30 strains from 10 antibiotic-naive infants; 27 from 9 antibiotic-treated outpatient infants; 30 from 9 healthy elderly volunteers; and 28 from 9 hospitalized elderly patients. The MIC values of ampicillin, cefuroxime, cefotaxime, gentamicin, ciprofloxacin, and sulfamethoxazole were measured by E-test and IntI1 was detected by PCR.

Results

Out of the 115 strains, 56 (49%) carried class 1 integron genes. Comparing persons without medical interventions, we found in antibiotic-naive children a significantly higher frequency of integron-bearing strains and MIC values than in healthy elderly persons (53% versus 17%; p < 0.01). Evaluating medical interventions, we found a higher resistance and frequency of integrons in strains from hospitalized elderly persons compared with non-hospitalized ones. Children treated with antibiotics had strains with higher MIC values (when compared with antibiotic-naive ones), but the integron-bearing in strains was similar. In most cases, the differences in resistance between the groups (integron-positive and negative strains separately) were higher than the differences between integron-positive and negative strains within the groups.

Conclusion

The prevalence of integrons in commensal E. coli strains in persons without previous medical intervention depended on age. The resistance of integron-carrying and non-carrying strains is more dependent on influencing factors (hospitalization and antibiotic administration) in particular groups than merely the presence or absence of integrons.

Major depressive disorder: probiotics may be an adjuvant therapy

Major depressive disorder (MDD) is an extremely complex and heterogeneous condition. Emerging research suggests that nutritional influences on MDD are currently underestimated. MDD patients have been shown to have elevated levels of pro-inflammatory cytokines, increased oxidative stress, altered gastrointestinal (GI) function, and lowered micronutrient and omega-3 fatty acid status. Small intestinal bacterial overgrowth (SIBO) is likely contributing to the limited nutrient absorption in MDD. Stress, a significant factor in MDD, is known to alter GI microflora, lowering levels of lactobacilli and bifidobacterium. Research suggests that bacteria in the GI tract can communicate with the central nervous system, even in the absence of an immune response. Probiotics have the potential to lower systemic inflammatory cytokines, decrease oxidative stress, improve nutritional status, and correct SIBO. The effect of probiotics on systemic inflammatory cytokines and oxidative stress may ultimately lead to increased brain derived neurotrophic factor (BDNF). It is our contention that probiotics may be an adjuvant to standard care in MDD.

Chronic fatigue syndrome: lactic acid bacteria may be of therapeutic value

Chronic fatigue syndrome (CFS) is complex illness with unknown aetiology. Recent research shows that patients with CFS have marked alterations in microbial flora, including lowered levels of bifidobacteria and small intestinal bacterial overgrowth (SIBO). Research also indicates that CFS patients are under increased oxidative stress, have a type 2 helper cell dominate cytokine profile, frequently report allergies, have altered essential fatty acid (EFA) status and may have malabsorption of certain micronutrients. Lactic acid bacteria (LAB) have the potential to influence the immune system in CFS patients by supporting T helper cell 1 driven cellular immunity and may decrease allergies. In addition LAB are strong antioxidants, may improve EFA status, can enhance absorption of micronutrients by protecting the intestinal epithelial barrier, and have been used to treat SIBO. It is our contention that LAB may have a therapeutic role in the treatment of CFS.

Problems of microbial ecology in man space mission

The state of microflora should be considered as one of the important links in chain of the specific functional disorders involving the spaceflight factors effects. At the same time, there occurs an establishment of nonspecific disbiotic response of the human microflora in the space flights of various duration characterized by a decrease up to a reduction of the "defense" group of microorganisms; by an appearance of unusual microorganisms in various biotypes, by accumulation of the potential of pathogenic species of automicroflora with their succeeding colonization and long term persistence. In experimental animal models to simulate dysbacteriosis and with the use of SPF-rats and primates flow aboard Cosmos biosatellites, the significance of indigenous microflora for preserving microecological homeostasis. Theoretically based and experimentally proven need for increasing the colonization resistance is confirmed by the practical use of the measures to stabilize microflora of the cosmonauts during space flights.