A general consensus exists that IBD is associated with compositional and metabolic changes in the intestinal microbiota (dysbiosis). However, a direct causal relationship between dysbiosis and IBD has not been definitively established in humans. Findings from animal models have revealed diverse and context-specific roles of the gut microbiota in health and disease, ranging from protective to pro-inflammatory actions. Moreover, evidence from these experimental models suggest that although gut bacteria often drive immune activation, chronic inflammation in turn shapes the gut microbiota and contributes to dysbiosis. The purpose of this Review is to summarize current associations between IBD and dysbiosis, describe the role of the gut microbiota in the context of specific animal models of colitis, and discuss the potential role of microbiota-focused interventions in the treatment of human IBD. Ultimately, more studies will be needed to define host-microbial relationships relevant to human disease and amenable to therapeutic interventions.

Gut microbiota and IBD: causation or correlation?

Background—Perinuclear antineutrophil cytoplasmic autoantibodies (pANCA) are a well recognised marker for ulcerative colitis. Antibodies to oligomannosidic epitopes of the yeast Saccharomyces cerevisiae (ASCA) are a new marker associated with Crohn's disease. 
Aims—To assess the value of detecting pANCA and/or ASCA for the diagnosis of ulcerative colitis and Crohn's disease. 
Methods—Serum samples were obtained from 100 patients with Crohn's disease, 101 patients with ulcerative colitis, 27 patients with other miscellaneous diarrhoeal illnesses, and 163 healthy controls. Determination of pANCA and ASCA was performed using the standardised indirect immunofluorescence technique and an ELISA, respectively. 
Results—The combination of a positive pANCA test and a negative ASCA test yielded a sensitivity, specificity, and positive predictive value of 57%, 97%, and 92.5% respectively for ulcerative colitis. The combination of a positive ASCA test and a negative pANCA test yielded a sensitivity, specificity, and positive predictive value of 49%, 97%, and 96% respectively for Crohn's disease. Among patients with miscellaneous non-inflammatory bowel disorders, three were ASCA positive and two were pANCA positive. One control was ASCA positive. The presence of ASCA in patients with Crohn's disease was associated with small bowel involvement. 
Conclusion—ASCA and pANCA are strongly associated with Crohn's disease and ulcerative colitis, respectively. Combination of both tests could help the diagnosis of inflammatory bowel disease. 



Keywords: Crohn's disease; ulcerative colitis; antineutrophil cytoplasmic autoantibodies; anti-Saccharomyces cerevisiae mannan antibodies

https://gut.bmj.com/content/gutjnl/42/6/788.full.pdf

Anti-Saccharomyces cerevisiae mannan antibodies combined with antineutrophil cytoplasmic autoantibodies in inflammatory bowel disease: prevalence and diagnostic role

Antibodies to CBir1 flagellin define a unique response that is associated independently with complicated Crohn's disease.

https://www.gastrojournal.org/article/S0016-5085(02)00159-2/pdf

Selected loss of tolerance evidenced by Crohn's disease-associated immune responses to auto- and microbial antigens.

Background. Saccharomyces cerevisiae is well known in the baking and brewing industry and is also used as a probiotic in humans. However, it is a very uncommon cause of infection in humans. Methods. During the period of 15–30 April 2003, we found 3 patients with S. cerevisiae fungemia in an intensive care unit (ICU). An epidemiological study was performed, and the medical records for all patients who were in the unit during the second half of April were assessed. Results. The only identified risk factor for S. cerevisiae infection was treatment with a probiotic containing Saccharomyces boulardii (Ultralevura; Bristol-Myers Squibb). This probiotic is used in Europe for the treatment and prevention of Clostridium difficile–associated diarrhea. The 3 patients received the product via nasograstric tube for a mean duration of 8.5 days before the culture result was positive, whereas only 2 of 41 control subjects had received it. Surveillance cultures for the control patients admitted at the same time did not reveal any carriers of the yeast. Strains from the probiotic capsules and the clinical isolates were identified as S. cerevisiae, with identical DNA fingerprinting. Discontinuation of use of the product in the unit stopped the outbreak of infection. A review of the literature identified another 57 cases of S. cerevisiae fungemia. Overall, 60% of these patients were in the ICU, and 71% were receiving enteral or parenteral nutrition. Use of probiotics was detected in 26 patients, and 17 patients died. Conclusions. Use of S. cerevisiae probiotics should be carefully reassessed, particularly in immunosuppressed or critically ill patients. Saccharomyces cerevisiae is a well-known yeast used in the food industry. It has now been demonstrated that this yeast can cause different forms of invasive infection [1–3], frequently after administration as a probiotic for the treatment of antibiotic-related diarrhea [4]. We report an outbreak of S. cerevisiae fungemia in an intensive care unit (ICU) that was traced, by means of molecular methods, to the use of probiotics, and we review all cases of S. cerevisiae fungemia that have been reported in the literature.

http://users.med.up.pt/cc04-10/MicroTextosApoio/Fungemia.pdf

Saccharomyces cerevisiae Fungemia: An Emerging Infectious Disease

Comparaison de 55 cas de maladie de Crohn, 40 de colite ulcerative et 30 temoins normaux. Les titres d'anticorps IgG et IgA contre Saccharomyces cerevisiae sont significativement eleves dans la maladie de Crohn, non dans la colite ulcerative

https://www.bmj.com/content/bmj/297/6656/1105.full.pdf

J. Main

Papers

Antibody to Saccharomyces cerevisiae (bakers' yeast) in Crohn's disease.