AIM:To investigate the correlations between selfreported symptoms of irritable bowel syndrome(IBS) and the gastrointestinal(GI) microbiota composition.METHODS:Fecal samples were collected from a total of 44 subjects diagnosed with IBS.Their symptoms were monitored with a validated inflammatory bowel disease questionnaire adjusted for IBS patients.Thirteen quantitative real-time polymerase chain reaction assays were applied to evaluate the GI microbiota composition.Eubacteria and GI bacterial genera(Bifidobacterium,Lactobacillus and Veillonella),groups(Clostridium coccoides/Eubacterium rectale,Desulfovibrio desulfuricans) and distinct bacterial phylotypes [closest 16S rDNA sequence resemblance to species Bifidobacterium catenulatum,Clostridium cocleatum,Collinsella aerofaciens(C.aerofaciens),Coprococcus eutactus(C.eutactus),Ruminococcus torques and Streptococcus bovis ] with a suspected association with IBS were quantified.Correlations between quantities or presence/absence data of selected bacterial groups or phylotypes and various IBSrelated symptoms were investigated.RESULTS:Associations were observed between subjects’ self-reported symptoms and the presence or quantities of certain GI bacteria.A Ruminococcus torques(R.torques)-like(94% similarity in 16S rRNA gene sequence) phylotype was associated with severity of bowel symptoms.Furthermore,among IBS subjects with R.torques 94% detected,the amounts of C.cocleatum 88%,C.aerofaciens-like and C.eutactus 97% phylotypes were significantly reduced.Interesting observations were also made concerning the effect of a subject’s weight on GI microbiota with regard to C.aerofaciens like phylotype,Bifidobacterium spp.and Lactobacillus spp.CONCLUSION:Bacteria seemingly affecting the symptom scores are unlikely to be the underlying cause or cure of IBS,but they may serve as biomarkers of the condition. AIM: To investigate the correlations between selfreported symptoms of irritable bowel syndrome (IBS) and the gastrointestinal (GI) microbiota composition. METHODS: Fecal samples were collected from a total of 44 subjects diagnosed with IBS.Their symptoms were monitored with a validated inflammatory bowel disease questionnaire adjusted for IBS patients. Thirteen quantitative real-time polymerase chain reaction assays were applied to evaluate the GI microbiota composition. Eubacteria and GI bacterial genera (Bifidobacterium, Lactobacillus and Veillonella), groups (Clostridium coccoides / Eubacterium rectale, Desulfovibrio desulfuricans) and distinct bacterial phylotypes [closest 16S rDNA sequence resemblance to species Bifidobacterium catenulatum, Clostridium cocleatum, Collinsella aerofaciens (C. aerofaciens), Coprococcus eutactus (C. effutus), Ruminococcus torques and Streptococcus bovis] with a suspected association between IBS were quantified. Corlations quantities or presence / absence data of sele cted bacterial groups or phylotypes and various IBSrelated symptoms were investigated .RESULTS: Associations were observed between subjects’ self-reported symptoms and the presence or quantities of certain GI bacteria. A Ruminococcus torques (R.torques) -like (94% similarity in 16S rRNA gene sequence) was associated with severity of bowel symptoms. Amongrther among among IBS subjects with R. torques 94% detected, the amounts of C. cocleatum 88%, C. aerofaciens-like and C. effutus 97% phylotypes were significantly reduced .Interesting observations were also made concerning the effect of a subject’s weight on GI microbiota with regard to C.aerofaciens like phylotype, Bifidobacterium spp. And Lactobacillus spp.CONCLUSION: Bacteria seemingly affecting the symptom scores are unlikely to be the underlying cause or cure of IBS, but they may serve as biomarkers of the condition.