Microbiota in health and irritable bowel syndrome: current knowledge,perspectives and therapeutic options

Abstract

The gastrointestinal tract is a natural reservoir of microbiota. The gut is germ-free at birth, but rapidly becomes host to various bacteria establishing a progressively mutual relationship. The composition of gut microbiota is individual-specific and depends on the genotype of the host and environmental factors. Novel techniques have been used to characterize gastrointestinal microbiota, including genomic approaches. The bacterial profile shows that dominant and minor phyla are present in the gastrointestinal tract. From the proximal to the distal segments of the gut the bacterial density gradually increases, reaching an estimated 10¹¹ to 10¹² bacteria per gram of colonic content. Dynamic interactions between gut and microbiota play a physiological role in metabolic, protective and structural functions, while dysbiosis contributes to several diseases. Microbiota appear to play a role in IBS, where qualitative and quantitative changes of bacteriaoccur in IBS subtypes. Initial therapeutic approaches in IBS have focused on microbiota. The relationship between perturbations of the microbiota, mucosal inflammation and IBS remains to be further investigated.     

Post-infectious irritable bowel syndrome

Post-infectious irritable bowel syndrome （PI-IBS） is a common disorder wherein symptoms of IBS begin after an episode of acute gastroenteritis. Published studies have reported incidence of PI-IBS to range between 5% and 32%. The mechanisms underlying the development of PI-IBS are not fully understood, but are believed to include persistent sub-clinical inflammation, changes in intestinal permeability and alteration of gut flora. Individual studies have suggested that risk factors for PI-IBS include patients＇ demographics, psychological disorders and the severity of enteric illness. However, PI-IBS remains a diagnosis of exclusion with no specific disease markers and, to date, no definitive therapy exists. The prognosis of PI- IBS appears favorable with spontaneous and gradual resolution of symptoms in most patients.     

褪黑激素与肠易激综合征

肠易激综合征是一种原因不明的慢性肠功能紊乱性疾病，其发病机制尚不清楚。其治疗方法也在不断改进中，褪黑激素对肠易激综合征的治疗有着积极的作用。     

The irritable bowel syndrome

The irritable bowel syndrome (IBS) is a familiar problem in the clinic, but as a disease entity it remains ill defined. Much confusion has arisen in the past, because of the inappropriate inclusion within the category of IBS of almost any patient with unexplained abdominal discomfort. Recent work has established that IBS patients can be positively identified by a cluster of specific symptoms. With the use of these criteria, it seems likely that IBS patients suffer from a diffuse motor abnormality of the gut associated with visceral hypersensitivity; although there is no associated psychopathology, a central nervous system component to the disorder is possible. Better insight into IBS promises more effective management.     

Diagnosing irritable bowel syndrome

It is often possible to positively diagnose irritable bowel syndrome (IBS) based on a combination of multiple symptoms and their chronic nature. Both the Manning criteria and the ROME 1999 Consensus Working Party Diagnostic Criteria help in diagnosing IBS. It is important that, during the first visit, possible contributing factors, such as associated psychosocial stress or a history of mental, physical, or sexual abuse, are considered as part of the patient evaluation. Patients need to receive a clear explanation of the possible causes of symptoms, the benign nature of IBS, and the low likelihood of serious underlying disease. An interactive, positive physician-patient relationship has a beneficial effect on the course of IBS and may be associated with a decreased need for future health care visits.     

Post-infectious irritable bowel syndrome

Irritable bowel syndrome (IBS) affects 8% to 22% of the general population. Although patients describe an insidious onset of symptoms, including abdominal pain relieved with bowel movements, excessive intestinal gas, variable bowel habits, and abdominal bloating, a subgroup of individuals describe the onset of IBS symptoms following an episode of acute gastroenteritis, known as post-infectious IBS (PI-IBS). Several studies have demonstrated the development of IBS following infection. Risk factors for the development of PI-IBS are female sex and longer duration of initial illness. Although the underlying mechanism of PI-IBS is unclear, ongoing inflammation is clearly a factor in the pathogenesis. The underlying inflammatory process results in increased enterochromaffin cells, T-lymphocytes, intestinal permeability, colonic transit time, and a variety of immunologic abnormalities. PI-IBS patients tend to have a better prognosis than do those with idiopathic IBS, with resolution of symptoms within 5 to 6 years. Treatment is similar to that of idiopathic IBS.     

Post-infectious irritable bowel syndrome

Irritable bowel syndrome (IBS) is a common disorder associated with abdominal pain or discomfort and altered bowel habits. The majority of patients describe an insidious onset of symptoms; however, a subset report a fairly precise time of onset following an attack of acute gastroenteritis. Typically, the potential acute infectious symptoms, such as fever and vomiting, resolve after several days, but abdominal discomfort, bloating, and diarrhea persist. Although the underlying mechanism of post-infectious IBS (PI-IBS) has not been established, ongoing inflammation appears to play a role, with an increase in serotonin-containing enterochromaffin cells, T lymphocytes, mast cells, proinflammatory cytokines, and intestinal permeability. Psychiatric comorbidities are less common in PI-IBS, compared with IBS patients in general; however, the prevalence of psychological disorders is still higher compared with that in the general population and is associated with a poorer prognosis. Overall, patients with PI-IBS have a slightly improved prognosis compared with those with IBS without an infectious onset.     

Probiotics and irritable bowel syndrome

Irritable bowel syndrome(IBS)is common gastrointestinal problems.It is characterized by abdominal pain or discomfort,and is associated with changes in stool frequency and/or consistency.The etiopathogenesis of IBS may be multifactorial,as is the pathophysiology,which is attributed to alterations in gastrointestinal motility,visceral hypersensitivity,intestinal microbiota,gut epithelium and immune function,dysfunction of the brain-gut axis or certain psychosocial factors.Current therapeutic strategies are often unsatisfactory.There is now increasing evidence linking alterations in the gastrointestinal microbiota and IBS.Probiotics are living organisms which,when ingested in certain numbers,exert health benefits beyond inherent basic nutrition.Probiotics have numerous positive effects in the gastrointestinal tract.Recently,many studies have suggested that probiotics are effective in the treatment of IBS.The mechanisms of probiotics in IBS are very complex.The purpose of this review is to summarize the evidence and mechanisms for the use of probiotics in the treatment of IBS.     

感染后肠易激综合征

越来越多的流行病学和临床资料表明早期胃肠道感染与肠易激综合征(irritable bowel syndrome,IBS)的关系密切。大部分胃肠道感染患者能够很快恢复并且无后遗症,但是仍有一部分患者会有持续性的症状,符合IBS的诊断标准,即为感染后肠易激综合征(post-infectious irritable bowel syndrome,PI-IBS)。本文综合国内外有关PI-IBS的研究进展,从PI-IBS的流行病学特征、相关危险因素、病理生理学改变以及临床特征等方面进行作一概述。     

肠易激综合征的研究方向

肠易激综合征 (ｉｒｒｉｔａｂｌｅｂｏｗｅｌｓｙｎｄｒｏｍｅ ,ＩＢＳ)是由腹部不适或腹痛伴排便异常组成的一组肠功能紊乱综合征 ,无任何器质性或异常的生化指标。过去曾被称为“过敏性结肠”、“易激结肠”或“黏液性结肠炎”等 ,现规范统称为“肠易激综合征”。国际上对该病的诊断标准曾多次研究制订 ,于 2 0 0 0年公布了最新的罗马Ⅱ诊断标准[1] 。其要点为 :(1)诊断本病首先需排除有组织结构或生化异常的器质性疾病 ;(2 )1年内至少要累积 3个月有反复发作的腹痛或腹部不适并伴有下列排便异常中的 2项指标 :①便后腹痛缓解或减轻 ,②…     

老年肠易激综合征

肠易激综合征是由腹部不适或腹痛伴排便异常组成的一组肠功能障碍性综合征,不能用任何结构异常或生化异常来解释。过去曾被称之谓“过敏性结肠”、“易激结肠”或“黏液性结肠炎”等,现规范统称之谓“肠易激综合征”（irritable bowel syndrome。IBS）^[1]。这是一种发病率高,时常影响终生的胃肠道疾病。流行病学研究提示年龄增长伴随IBS发病率减低（可能和老年人痛觉改变有关）,但1BS始终是老年人常见的胃肠道疾病。     

Postinfectious irritable bowel syndrome

A small but significant subgroup of patients with irritable bowel syndrome (IBS) report a sudden onset of their IBS symptoms after a bout of gastroenteritis. Population-based surveys show that although a history of neurotic and psychologic disorders, pain-related diseases, and gastroenteritis are all risk factors for developing IBS, gastroenteritis is the most potent. More toxigenic organisms increase the risk 11-fold, as does an initial illness lasting more than 3 weeks. Hypochondriasis and adverse life events double the risk for postinfective (PI)-IBS and may account for the increased proportion of women who develop this syndrome. PI-IBS is associated with modest increases in mucosal T lymphocytes and serotonin-containing enteroendocrine cells. Animal models and some preliminary human data suggest this leads to excessive serotonin release from the mucosa. Both the histologic changes and symptoms in humans may last for many years with only 40% recovering over a 6-year follow-up. Celiac disease, microscopic colitis, lactose intolerance, early stage Crohn's disease, and bile salt malabsorption should be excluded, as should colon cancer in those over the age of 45 years or in those with a positive family history. Treatment with Loperamide, low-fiber diets, and bile salt- binding therapy may help some patients. Serotonin antagonists are logical treatments but have yet to be evaluated.     

Diet and the irritable bowel syndrome

Food intake plays a key role in triggering or perpetuating symptoms in patients with IBS. Evaluation of the impact of diet in the individual patient requires a precise dietary history and a 7-day prospective dietary analysis, which should include the quality and quantity of food consumed, chronologic sequence and nature of symptoms, and the frequency and consistency of bowel movements. The caloric density of the meal, total fat intake, the quantity and quality of lactose-containing foods, sorbitol, fructose, and the nature and quantity of soluble and insoluble fiber intake must be noted. Patients with reflux esophageal symptoms should eliminate foods that decrease LES pressure, such as chocolate, peppermint, alcohol, and coffee. Direct esophageal mucosal irritants such as tomatoes, citrus juices, sharp condiments, and alcohol should be limited. Gastric emptying is slowed with the ingestion of fats and soluble fiber. Small bowel motility is slowed by soluble fiber and fatty foods. Gaseous syndromes may be reduced by avoidance of smoking, chewing gum, excessive liquid intake, and carbonated drinks. The reduced intake of large amounts of lactose-containing foods, sorbitol, and fructose may limit postprandial bloating. Flatus production can be lowered by reducing fermentable carbohydrates such as beans, cabbage, lentils, brussel sprouts, and legumes. Soluble and insoluble fiber ingestion will reduce sigmoidal intraluminal pressures and overcome spastic constipation when given in progressive graded doses. Effective dietary manipulations remain a key factor in reducing symptoms in IBS.     

Comorbidity in irritable bowel syndrome

BACKGROUND: Comorbid nongastrointestinal symptoms account for two-thirds of excess health-care costs in irritable bowel syndrome (IBS). OBJECTIVES: To determine whether IBS patients are at greater risk for specific comorbid disorders versus showing a general tendency to overreport symptoms; whether patients with inflammatory bowel disease (IBD) show patterns of comorbidity similar to IBS; whether comorbidity is explained by psychiatric disease; and whether excess comorbidity occurs in all IBS patients. METHODS: All 3,153 patients in a health maintenance organization with a diagnosis of IBS in 1994-1995 were compared to 3,153 age- and gender-matched controls, and to 571 IBD patients. All diagnoses in a 4-yr period beginning 1 yr before their index visit were categorized as gastrointestinal, psychiatric, or nongastrointestinal somatic. Nongastrointestinal somatic diagnoses were further divided into symptom-based versus biological marker-based diagnoses. RESULTS: Forty-eight of 51 symptom-based and 16 of 25 biomarker-based diagnoses were significantly more common in IBS versus controls. However, there were no unique associations. Bacterial, viral, and fungal infections and stroke were among diagnoses made more frequently in IBS. IBD patients were similar to controls. Greater somatic comorbidity was associated with concurrent psychiatric diagnosis. Only 16% of IBS patients had abnormally high numbers of comorbid diagnoses. CONCLUSIONS: Comorbidity in IBS is due to a general amplification of symptom reporting and physician consultation rather than a few unique associations; this suggests biased symptom perception rather than shared pathophysiology. Comorbidity is influenced by, but is not explained by, psychiatric illness. Excess comorbidity is present in only a subset of IBS patients.     

Management of irritable bowel syndrome

Irritable bowel syndrome (IBS) is one of the most common functional gastrointestinal disorders. The prevalence rate is 10-20% and women have a higher prevalence. IBS adversely affects quality of life and is associated with health care use and costs. IBS comprises a group of functional bowel disorders in which abdominal discomfort or pain is associated with defecation or a change in bowel habit, and with features of disordered defecation. The consensus definition and criteria for IBS have been formalized in the "Rome II criteria". Food, psychiatric disorders, and gastroenteritis are risk factors for developing IBS. The mechanism in IBS involves biopsychosocial disorders; psychosocial factors, altered motility, and heightened sensory function. Brain-gut interaction is the most important in understanding the pathophysiology of IBS. Effective management requires an effective physician-patient relationship. Dietary treatment, lifestyle therapy, behavioral therapy, and pharmacologic therapy play a major role in treating IBS. Calcium polycarbophil can benefit IBS patients with constipation or alternating diarrhea and constipation.