functional bowel disorders , including irritable bowel syndrome ( ibs ) , are common gastrointestinal disorders all over the world . however , in the last few decades , advances in our understanding of the pathophysiology of ibs have revealed several factors , including alterations in the microbiota , as potentially relevant to the cause of this syndrome and the precipitation of its symptoms . indeed , alterations in the gut microbiota are being increasingly implicated in the pathogenesis of several gastrointestinal and systemic diseases . we wish , therefore , to review the gut microbiota and its alterations in , and relationships to , ibs . the human gut harbours a huge microbial ecosystem , which is equipped to perform a variety of functions such as the digestion of food , metabolism of the drugs , detoxification of toxic compounds , production of essential vitamins , prevention of attachment of pathogenic bacteria to the gut wall and maintenance of homeostasis in the gastrointestinal tract ( git ) [ 13 ] . the human gut is first colonized at birth ; this microbiota gradually increases in size and diversity up to the end of the first year of life ; by that time , the gut microbiota has come to resemble that of the adult and remains relatively stable thereafter . the composition of the gut microbiota varies according to age , sex , diet , geographical origin of the individual and is also influenced by certain environmental factors , such as administration of antibiotics . there are 10  times more microbial cells ( 10 ) in the gut than cells in the entire body ( 10 ) . a recent study has suggested that the human gut microbiota consists of more than 35,000 bacterial species and that 70% of all of microbes in the human body reside in the colon . the small intestine consists of mainly gram - positive and aerobic bacteria , whereas the large intestine consists largely of gram - negative and strictly anaerobic bacteria [ 5 , 6 ] . alterations in the normal gut microbiota have been suggested as etiologic factors in the development of functional gastrointestinal disorders such as ibs and functional dyspepsia , common gi disorders of unknown etiology [ 79 ] . quantitative alterations in the gut microbiota in the small bowel may result in the clinical syndrome recognized as small intestinal bacterial overgrowth ( sibo ) . in sibo , such is the change in the number and type of bacteria in the upper small intestine that diarrhea , abdominal bloating , malabsorption , abdominal pain , and excessive gas production result ; severe motor dysfunction may be an underlying cause [ 1113 ] . quantitative changes in the colonic microbiota may lead to the proliferation and development of specific species that produce more short - chain fatty acids ( scfas ) and gases , such as methane , hydrogen , and carbon dioxide , potentially resulting in abdominal bloating and distension . an increase in the concentration of scfas ( acetate , butyrate , and propionate ) leads to acidification of the colon and deconjugation of bile acid . this in turn may cause significant changes in water and electrolyte transport in the colon which result in diarrhea [ 8 , 14 , 15 ] . malabsorption of carbohydrates may cause increased production of hydrogen gas , which is associated mainly with diarrhea - predominant ibs ( ibs - d )   whilst excess methane gas production is associated with constipation - predominant ibs ( ibs - c ) . ibs is a functional gastrointestinal disorder associated with abdominal discomfort or pain , distension and bloating , diarrhea , constipation , or mixed bowel habits ( i.e. , both constipation and diarrhea ; ibs - m ) . ibs subjects may also experience greater levels of stress , anxiety , and depression compared to healthy subjects [ 16 , 17 ] . all of these co - morbidities are associated with impaired quality of life in ibs patients [ 1820 ] . several diagnostic criteria ( kruis , manning , rome ) have been used to distinguish ibs patients from those with organic bowel disease in daily clinical practice [ 11 , 21 ] . the prevalence of ibs varies from 9% to 22% in the united states and europe [ 22 , 23 ] . in asian countries , the lowest prevalence has been reported from india , at 4.2% , and the highest from japan and singapore [ 2325 ] . several hypotheses have been proposed which include alteration in the gut microbiota , dysregulation of the brain - gut axis and autonomic nervous system , visceral hypersensitivity , and altered levels of gastrointestinal neuropeptides and hormones [ 11 , 22 , 26 ] . furthermore , abnormal gastrointestinal motility , as well as genetic , environmental , and psychological factors , may also play important roles in the development of ibs . recent studies have also shown that ibs is associated with low - grade intestinal inflammation resulting from an activated immune system , in response to a normal or abnormal gut microbiota [ 1 , 27 , 28 ] . there is a growing interest in investigating the role of an altered gut microbiota in the pathogenesis of ibs [ 14 , 29 ] . normal gut microbiota have either direct bactericidal effects or can prevent the adherence of pathogenic bacteria to the wall of the gastrointestinal tract [ 7 , 30 , 31 ] . dysbiosis in the gut may facilitate the adhesion of enteric pathogens in the human gut which can be associated with ibs symptoms [ 30 , 32 ] . alteration in the composition of the normal microbiota and disturbed colonic fermentation in ibs patients may play an important role in development of ibs symptoms . firmicutes and bacteroidetes are the major beneficial gut microbiota in the normal human and changes in their relative numbers have been reported in ibs patients . significantly , a two - fold increase in the ratio of firmicutes to bacteroidetes has been reported in ibs patients . this results from an increase in the quantity of ruminococcus , clostridium , dorea species and a decrease in the quantity of bifidobacterium and faecalibacterium species . significantly greater abundance of classes of gammaproteobacteria and enterobacteriaceae in healthy controls were positively correlated with the inflammatory markers il-6 and il-8 . higher levels of these cytokines have been reported in ibs patients [ 34 , 35 ] . due to a different microenvironment in the intestinal epithelium and lumen , the composition of microbiota is not the same at the level of the gut epithelium and lumen . culture - based analysis had shown that there were significant differences between the mucosa - associated microbiota and fecal samples in both healthy control and ibs patients . for example , a significantly increased quantity of aerobic bacteria and lactobacillus was noted in ibs - d in feces but not in mucosal samples . several studies using different methodologies to define changes in the microbiota have been published , including classic culture - based techniques , pcr - based molecular technologies such as real - time pcr ( q pcr ) , microarray , dgge ( denaturation gradient gel electrophoresis ) , gc profiling , and high - throughput sequencing based on 16  s rrna [ 33 , 36 ] ( see table 1 ) . bacterial fermentation of undigested , unabsorbed food causes production of scfas , which are bacteriostatic for a group of species , either directly or by reducing ph [ 2 , 7 , 30 , 31 , 37 ] . a previous study reported that the prevalence of sibo in ibs subjects detected by lactulose hydrogen breath test was about 78% . however , this study used the lactulose hydrogen breath test which has now been shown to be prone to a high rate of false positive result   and may have led to an overestimation of its frequency . ibs develops in a subgroup of individuals following an episode of acute gastrointestinal infection , known as pi - ibs . acute enteric infections are characterized by abdominal discomfort , fever , vomiting , bloating , and diarrhea , [ 14 , 39 , 40 ] . fever and vomiting generally improve after a few days while abdominal discomfort , diarrhea and bloating  persist  in those who develop pi - ibs . risk factors for the development of pi - ibs include younger age , female gender , prolonged duration of diarrhea , the presence of bacterial pathogens , and psychological morbidities including anxiety , frustration , and depression [ 4143 ] . the risk of ibs increased sixfold after an acute gastrointestinal infection and persists for up to 3 years [ 44 , 45 ] . recent studies have shown that pi - ibs develops in 330% of individuals with bacterial gastroenteritis caused by a number of enteric pathogens such as campylobacter species , clostridium perfringens , staphylococcus aureus , bacillus cereus , shigella and viruses [ 7 , 30 , 32 , 39 ] . the prevalence of pi - ibs in subjects who had suffered from diarrhea whilst travelling in developing countries has been estimated to be 714% . the diagnosis of pi - ibs was made according to rome criteria for ibs among individuals who did not have ibs previously but developed it after the episode of acute gastroenteritis [ 14 , 39 ] . recent studies have suggested that pi - ibs is associated with dysbiosis in the gut ( induced either by enteric infection or by the use of antibiotics ) , psychological factors ( such as stress , anxiety , and depression ) , genetic susceptibility of the host , persistent activation of the host immune system , increased intestinal permeability , and an increased number of enterochromaffin cells in the gut [ 22 , 39 , 47 ] . potentially harmful microorganisms and their metabolites cause the disruption of tight junctions between epithelial cells leading to increased mucosal permeability during the acute phase of infection [ 48 , 49 ] . the permeability of the proximal small intestine in pi - ibs was shown to be significantly increased compared to controls . a lesser expression of zo-1 has been observed in biopsy samples of ibs subjects . as a result of increased permeability of intestinal epithelial cells , an influx of immune cells including mast cells , t lymphocytes , macrophages , and inflammatory mediators such as il-2 , il-1 , il-6 , il10 , tgf- occurs after an acute enteric infection [ 48 , 49 , 52 , 53 ] . a growing body of evidence indicates that mast cells and lymphocytes are increased in the mucosa of both pi - ibs and ibs patients . il-1 is significantly increased in pi - ibs patients during and after the infection compared with those subjects who do not develop pi - ibs . these inflammatory mediators ( il-1 , il-1 , il-6 , ifn- ) damage the intestinal epithelial barrier and cause inflammation . furthermore , the administration of antibiotics altered the composition of the gut microbiota and inhibited the expression of antimicrobial peptide reg iii  produced by commensal bacteria . reg iii  strengthens the intestinal epithelial barrier by inhibiting gram - negative pathogens but has no effect on gram - positive bacteria ; its inhibition results , therefore , in a favourable environment for enteric pathogens to proliferate [ 4 , 7 , 55 ] . normally , the density of bacteria is much lower in the small intestine than in the large intestine . there are 10 colony - forming units ( cfu ) per ml , 10  cfu / ml , 10  cfu / ml and 10  cfu / ml bacteria in the cecum , terminal ileum , proximal ileum , and jejunum / duodenum , respectively [ 54 , 56 ] . the major families of bacteria in the small intestine include bacilli , streptococcaceae , actinobacteria , actinomycinaea , and corynebacteriaceae . qualitative or quantitative changes in the microbiota of small intestine may lead to the clinical features of sibo [ 56 , 57 ] . in healthy individuals , the normal bacterial count in the proximal small intestine is 10  cfu / ml ; sibo is traditionally defined by a bacterial count of 10  cfu per ml in jejunal aspirate [ 2 , 56 ] . several techniques have been used for the diagnosis of sibo , which include the lactulose hydrogen ( lhbt ) , c xylose and glucose hydrogen ( ghbt ) breath tests and culture of jejunal aspirate [ 13 , 56 , 58 ] . hydrogen and methane are normally produced in the large intestine but in case of sibo these gases are produced in the small bowel also . methanobrevibacter smithii , methanobrevibacter stadtmanae , and , possibly , coliform bacteria produce methane gas [ 13 , 14 ] . the jejunal aspirate culture has , traditionally , been used as the gold standard to diagnose sibo . the limitations of this test however include invasiveness and the challenges posed by attempting to culture all strains and species [ 54 , 57 ] ; therefore , hydrogen breath tests ( ghbt or lhbt ) are most commonly used . in a study where endoscopic jejunal biopsy culture was used to diagnose sibo , the prevalence of sibo in ibs patients was 4% ( based on the definition of 10cfu / ml of bacteria in jejunal aspirate ) and no different from that seen in healthy individuals . in contrast , in a study of 111 ibs subjects using lhbt , pimentel et al . reported a prevalence of sibo of 84% in ibs ( in comparison to 20% in healthy individuals ) . recent published data have shown that , using jejunal aspirate as the gold standard , double - peak in lhbt only diagnoses one - third of sibo patients ; the sensitivity and specificity of lhbt were 31% and 86% and those of ghbt were 44% and 80% , respectively . in a separate study by berthold , the sensitivity and specificity of lactose-(13c ) ureide breath test ( lubt ) were 66.7% and 100% and those of ghbt 41.7% and 44.4% , respectively . the sensitivity and specificity after glucose were 62.5% and 82% and after lactulose were 52% and 86% , respectively . the variation in lhbt and ghbt may be due to differences in the diagnostic criteria used for selection of ibs patients , ecological origin , nature of the substrate used , and diagnostic methods . the administration of antibiotics and probiotics reduced not only gas - related problems but also ibs - like symptoms [ 54 , 56 , 61 , 64 ] . sibo may arise due to hypochlorhydria , altered intestinal motility [ 2 , 56 ] , altered bacteriostatic properties of pancreatic and biliary secretion , and a dysregulated immune response . proton pump inhibitors ( ppis ) may predispose to sibo by decreasing acid secretion in the stomach . theisen reported that the inhibition of acid secretion related to the administration of omeprazole led to an increased concentration of unconjugated bile acids . thus , the potential side effects of ppi include constipation , diarrhea , bloating , and abdominal pain , symptoms which resemble those of ibs   ( see table 2 ) . commensal bacteria provide a favourable environment , prevent the adherence of pathogenic bacteria , and modulate innate and adaptive immune responses [ 55 , 69 ] . the intestinal epithelium contains a large number of lymphocytes that can remove infected epithelial cells . paneth cells found at the base of the intestinal gland ( crypt of lieberkuhn ) throughout the small intestine can prevent the penetration of intestinal epithelium by commensal and pathogenic bacteria . iecs are protected by a glycocalyx layer of mucus , the epithelial junction adhesion complex , secretory iga , chloride secretion , and other glycoproteins [ 30 , 55 ] . the intestinal barrier consists of the tight junction complex , adherin junctions , gap junctions , and desmosomes . there are more than 40 types of proteins in the tight junction complex , which play crucial role in maintaining the permeability of the intestinal epithelium . a leaky intestinal epithelium has been reported in subjects with ibs , ulcerative colitis , crohn 's disease , celiac disease , and food - borne infections [ 7275 ] . a recent study has shown that microrna-29a regulates the permeability of the intestine through the generation of glutamine synthetase in patients with ibs . decreased concentration of glutamine leads to an increase in the permeability of intestinal epithelial cells ( iec ) , whilst the permeability of iecs can be recovered by the supplementation of glutamine in patients with ibs . the administration of probiotics , fermented milk ( streptococcus thermophilus , lactobacillus bulagaris lactobacillus acidophilus , and bifidobacterium longum ) and l. plantarum has been shown to strengthen the intestinal barrier [ 7274 ] . paneth cells and enterocytes in the gut secrete antimicrobial molecules such as angiogenin 4 , defensins , iga antibodies , and regiii . these antimicrobial peptides destroy pathogenic bacteria by forming a pore in the bacterial cell wall [ 7 , 55 , 76 ] . these data suggest that a symbiotic relationship is present between commensal bacteria and the host . the composition of the gut microbiota influences the development of the immune system . any alterations in the gut microbiota due to enteric infections , antibiotic therapy or acid suppressive treatment lead to activation of both the innate and adaptive immune responses . commensal bacteria from the phylum of bacteroidetes and firmicutes have been shown to induce t regulatory cells and inhibit th17-mediated inflammation . in contrast , the administration of bifidobacterium animalis subspecies inhibited intestinal inflammation via a reduction of the commensal bacteria enterobacteriace [ 55 , 77 , 78 ] . thus , the gut microbiota plays an important role in the maintenance of homeostasis of various subpopulations of t cells : regulatory t cells ( tregs ) , t helper 1 ( th1 ) , and t 17 ( th17 ) cells in the gut . low - grade inflammation in the intestine in ibs patients is associated with the activation of t lymphocytes and mast cells , increased expression of proinflammatory cytokines such as il-6 and il-8 , and elevated levels of il-1 , tnf- , and il-8 in peripheral blood mononuclear cells [ 80 , 81 ] . significantly increased levels of tnf- , il-1 , and il-6 , stimulated by lipopolysaccharide ( lps ) , have been reported in an ibs - d subgroup while increased levels of lps - stimulated il-1 were described in an ibs - c subgroup ( figure 1 ) . in pi - ibs , lps - induced cytokines ( tnf- , il-1 , and il-6 ) are significantly increased when compared with controls . increased concentrations of il-1 are associated with the development of ibs symptoms such as alteration in bowel habits . thymus - derived t regulatory cells ( treg ) are involved in the suppression of inflammation in ibs , ulcerative colitis , and crohn 's disease through the inhibition of t effector cells . it has been shown that t cells express high levels of cd25 tregs in the colon in ibs patients . therefore , any alteration in the frequency of tregs may lead to recruitment of immune effectors which , consequently , results in inflammation [ 83 , 84 ] . intestinal epithelial cells recognize pathogens by way of pattern recognition receptors including toll - like receptors ( tlrs ) and nucleotide - oligomerization - domain-(nod ) like receptors . they induce innate immune responses by the transcription and translation of antimicrobial proteins and the induction of proinflammatory cytokines and chemokines through the nf-b pathway [ 30 , 70 ] . ten tlrs have been reported in man so far , which recognized various microbial pathogens , including viruses , bacteria , fungi , and protozoa . a recent study has reported upregulation of tlr 4 and tlr 5 and down - regulation of tlr 7 and tlr 8 in ibs patients . increased levels of tlr 4 and tlr 5 indicate that their cognate ligands , lps and flagellin , are also increased in ibs patients . since the ligand for tlr 7 and tlr 8 is single - stranded rna , decreased level of tlr 7/8 suggested that viral infection may also play an important role in the development of ibs - like symptoms . these data further support that increased permeability is present in at least a subgroup of ibs patients [ 28 , 85 ] . -defensin 2 is an antimicrobial protein secreted by intestinal epithelial cells and induced by tlr 4 . increased levels of -defensin 2 have been reported in the intestine of patients with either ibs or ulcerative colitis [ 84 , 85 ] . several studies have shown that commensal bacteria may reduce inflammation , in part , by directly acting on dendritic cells to stimulate the induction of il-10 and regulatory t cells ( treg ) . with an increase in the number of commensal bacteria , dendritic cells provide signals to lymph nodes to stimulate adaptive immune responses leading to induction of iga antibodies that wrap the luminal antigens and , thus , prevent them from breaching the intestinal barrier and the inhibition of the systemic immune response . dendritic cells can directly sample luminal pathogens without disruption of tight junctions [ 30 , 55 , 86 ] . degranulation of mast cells releases histamine and other potent mediators that can influence the function of the enteric nervous system and smooth muscles , causing ibs - like symptoms . in addition , a study has shown that mast cells are significantly increased in the caecum in patients with ibs . tryptase , a protease released by mast cells , has been reported to be significantly increased in the colonic mucosa of patients with ibs . increased concentrations of serine protease the observation of dysbiosis in the gut microbiota , altered mucosal barrier function , activated immune responses , and sibo support a role for bacteria in the pathogenesis of ibs . probiotics are live or attenuated microorganisms which , when administered in sufficient quantities , have been shown to improve gut epithelial integrity , as well as alleviate the symptoms of ibs [ 30 , 8890 ] . previous studies have shown that the administration of adequate amounts of probiotics ( live microorganisms ) may alleviate the symptoms of ibs , suppress proinflammatory cytokines , and promote the integrity of the intestinal barrier [ 3 , 31 ] . one study showed that the consumption of bifidobacterium infantis 35624 was associated with proliferation of t regulatory cells , reduction of proinflammatory cytokines , down regulation of t cells , reduced expression of co - stimulatory molecules , and attenuation of nf-b . in vitro , increased levels of proinflammatory cytokines ( il-12 ) and decreased concentrations of the anti - inflammatory cytokine ( il-10 ) by pbmcs have been reported in ibs patients . the ratio of il-10/il-12 was altered in ibs patients compared to healthy volunteers and the administration of bifidobacterium infantis normalised this ratio . probiotics should have the following characteristics : ( 1 ) they must survive in the gastrointestinal tract following passage and eventually reside in the colon , ( 2 ) they must not have a major adverse effect on other beneficial bacteria in the gut , ( 3 ) they should be hostile to mutagenic or pathogenic organisms in the gut , and ( 4 ) they must be stable genetically . in clinical studies , probiotics have been shown to improve infectious or secretory diarrhea , traveller 's diarrhea , and antibiotic - induced diarrhea via a number of mechanisms that may include direct effects on gastrointestinal motility and the enteric nervous system . in a separate study , patients with ibs were treated with bifidobacterium infantis or lactobacillus salivarius ( 1e10 ) in malted milk or malted milk alone ( as a placebo ) for 8  weeks ; there was a significant reduction in abdominal pain , discomfort , bloating , distension , and bowel movement difficulty in patients who received bifidobacterium infantis compared with those who had placebo . vsl#3 contains a mixture of different bacterial species including lactobacillus species ( l. casei , l. plantarum , l. acidophilus , and l. delbrueckii ) , bifidobacterium species ( b. longum , b. breve , and b. infantis ) , and streptococcus thermophilus . a randomized controlled trial showed that the oral administration of vsl#3 , twice daily for 8  weeks , significantly reduced abdominal bloating , but not other parameters ( colonic transit time , bowel dysfunction , abdominal pain , flatulence , or urgency ) in a subgroup of diarrhea predominant ibs patients , when compared with placebo . in a second study targeting 48 ibs patients with bloating , vsl#3 significantly reduced flatulence and colonic transit compared with the placebo group . in summary , many clinical trials have investigated the therapeutic benefits of probiotics in patients with ibs . however , differences in duration of therapy , heterogeneity in species or strains of selected bacteria , and differences in characteristics of the enrolled patients have resulted in inconsistent results . prebiotics are nondigestible dietary supplements that affect the host by stimulating the growth of beneficial bacteria in the colon . prebiotics have the capability to stimulate only microbes which are already residing in the gut . prebiotics are fermented by host bacteria and have been associated with a reduction in the level of triglyceride , improvement of the postprandial glucose level and a reduction in intestinal permeability [ 3 , 95 ] . the fermentation of prebiotics leads to the production of scfas such as butyric acids , which can serve as energy source for intestinal epithelial cells . when galactooligosaccharides are used as prebiotics , they are known to stimulate gut bifidobacteria in ibs patients and , thereby , reduce the symptoms of ibs . a potential limitation of prebiotic treatment is that prebiotics undergo fermentation and could produce bloating and flatulence . one study has shown that a combination of bifidobacterium spp . and a prebiotic , inulin , significantly increased the quantity of bifidobacteria . furthermore , prebiotics also help passage of probiotics through the upper gastrointestinal tract and facilitate their establishment in the colon . is associated with dysbiosis and sibo , prokinetics could benefit ibs patients through an effect on the microbiota . however , studies reporting the use of erythromycin for the treatment of ibs have shown limited efficacy . furthermore , domperidone and cisapride were not always effective for the treatment of ibs . in any event , cisapride has been withdrawn from the market due to adverse cardiac effect . as discussed in previous sections , accumulating data support the role of bacteria in the etiology of ibs [ 102104 ] , and studies using antibiotics to target the intestinal microbiota to treat ibs are now emerging . in a double blind , randomized placebo - controlled study , neomycin was more effective than placebo in reducing ibs symptoms . however , the use of neomycin in the treatment of ibs has been limited by a marginal degree of efficacy above placebo and side effects . rifaximin , derived from rifamycin , is highly concentrated in the gut lumen and has little systemic absorption . it has been used in the treatment of traveller 's diarrhea and sibo . in a recent , large , double - blind , placebo - controlled trial , in which subjects were administered 550  mg rifaximin 3 times daily for 2  weeks and followed up for 10  weeks , there was a significant reduction in global ibs symptoms in the rifaximin group in comparison to placebo ( 40.8% versus 31.2% ) . in addition , there was a significantly greater reduction in bloating in those who received rifaximin compared to placebo ( 40.2% versus 30.3% ) [ 89 , 103 , 105 ] . a combination of probiotics and antibiotics may play a beneficial role in the treatment of ibs symptoms . probiotics may increase the efficiency of antibiotics and reduce gastrointestinal pathogens by the production of antibacterial molecules including bacteriocins . the literature on pi - ibs , sibo , the relationship between gut microbiota and gi sensorimotor functions , and the potential for probiotics and antibiotics to alter these functions and to improve some of the symptoms of ibs , taken together , provide strong evidence in support of a major role for the gut microbiota in the pathogenesis of ibs . this concept represents a potential paradigm shift in our understanding of the underlying mechanism ( for at least a subset of patients with ibs ) from that of ibs as an entirely psychosomatic disorder to that of a more organic disorder related to an altered gut microbiota and low - grade inflammation . this could , ultimately , lead to a potential change in the management of ibs to strategies that alter the gut microbiota and inflammation .
progress in the understanding of the pathophysiology of irritable bowel syndrome ( ibs ) , once thought to be a purely psychosomatic disease , has advanced considerably and low - grade inflammation and changes in the gut microbiota now feature as potentially important . 
 the human gut harbours a huge microbial ecosystem , which is equipped to perform a variety of functions such as digestion of food , metabolism of drugs , detoxification of toxic compounds , production of essential vitamins , prevention of attachment of pathogenic bacteria to the gut wall , and maintenance of homeostasis in the gastrointestinal tract . 
 a subset of patients with ibs may have a quantitative increase in bacteria in the small bowel ( small intestinal bacterial overgrowth ) . 
 qualitative changes in gut microbiota have also been associated with ibs . 
 targeting the gut microbiota using probiotics and antibiotics has emerged as a potentially effective approach to the treatment of this , hitherto enigmatic , functional bowel disorder . 
 the gut microbiota in health , quantitative and qualitative microbiota changes , and therapeutic manipulations targeting the microbiota in patients with ibs are reviewed in this paper .