Crohn's disease and ulcerative colitis are two of the most common inflammatory bowel diseases, the diagnosis of which can be confused by the similarities in their symptoms (diarrhea, rectal bleeding, abdominal pain, weight loss...). The results of a study by the Vall d'Hebron Research Institute (VHIR) have shown that patients with Crohn's disease have a different number of bacteria and fungi that are part of the intestinal microbiota compared to those with ulcerative colitis. This amount is also altered with respect to healthy people. Thus, quantifying the intestinal microbiota would be useful to facilitate the correct diagnosis of patients and offer them the appropriate treatment for their pathology. These findings have been published in https://msystems.asm.org/content/6/2/e01277-20 mSystems.The intestinal microbiota consists of a set of microorganisms that live in the digestive tract, including bacteria and some fungi, although the latter are found in smaller numbers. The researchers analyzed the number of these microorganisms in 294 stool samples from patients with Crohn's disease or ulcerative colitis, healthy relatives of patients, as well as from healthy people without relatives with inflammatory bowel disease. The Vall d'Hebron results were validated with patient samples from the Leuven University Hospital in Belgium.The work shows that Crohn's disease patients have fewer bacteria than healthy people, while in ulcerative colitis there is also a decrease in the number of bacteria, but an increase in the number of fungi. In addition, it was observed that, when a patient with ulcerative colitis suffers a flare, the fungal load increases even more. "By combining the information on the microbiota with the clinical data of the patients (results in medical tests, body mass index, lifestyle habits, etc.) we will have a great capacity to discriminate between Crohn's disease and ulcerative colitis. It will therefore help to diagnose the disease and also to predict if a flare is going to occur", highlights Dr. Chaysavanh Manichanh, head of the Intestinal Microbiota research line of the Physiology and Pathophysiology of the Digestive Tract group at the VHIR.This change in the abundance of microorganisms is also observed in healthy relatives of patients, although the difference is smaller than in patients. The study authors explain that this tendency may be due to genetic causes or the fact of sharing the place of residence and having lifestyles and diets similar to their relative. This could indicate a certain predisposition to the disease, although they will not necessarily develop it in the future. "We do not yet know if changes in the microbiota are a cause or consequence of inflammatory bowel disease. Probably many factors participate in the development of the disease, among them, genetic or environmental factors", point out Dr. Manichanh and Dr. Natalia Borruel, specialist of the Digestive System Service of the Vall d'Hebron University Hospital and researcher of the group of the Physiology and Pathophysiology of the Digestive Tract group at the VHIR.Previous studies by the Physiology and Pathophysiology of the Digestive Tract group confirmed that there are differences between the types of bacteria present in the intestine of patients with Crohn's disease and that identifying the profile of microorganisms would help in the diagnosis of the disease. However, as Dr. Manichanh explains, "to know what bacteria are in the intestine and the pathophysiology of the disease, it is necessary to perform a sequencing of some regions of the DNA of all microorganisms. This is feasible when we talk about research in the laboratory, but, for now, it is still very difficult to apply it to the clinic so that it reaches all patients quickly. This new method, based on a quantitative PCR, is much easier and adaptable to a clinical setting".Now, the objective of the researchers is to validate these results with a large number of samples, since the great variability of the microbiota between people makes a large-scale analysis necessary, including patients with different degrees of affectation and from different parts of the world. This will require collaboration between international centers working in this field.Crohn's and ulcerative colitis: two diseases with similar symptomsCrohn's disease and ulcerative colitis are two inflammatory bowel diseases. Both are characterized by intestinal inflammation, but while ulcerative colitis is limited to the colon and inflammatory changes appear mainly in the inner layer of the intestine (mucosa), Crohn's disease can affect any part of the digestive tract and the entire thickness of the intestinal wall. The first symptoms of both diseases can be the presence of blood in the stool, abdominal pain and diarrhea, which makes the differential diagnosis difficult, which is important for adequate and individualized follow-up and treatment. "The usual diagnosis requires a compatible endoscopy, radiological study (usually ultrasound, CT or MRI) and suggestive histological findings", concludes Dr. Luis Mayorga, specialist of the Digestive System Service of the Hospital Vall d'Hebron and researcher at the Physiology and Pathophysiology of the Digestive Tract group at the VHIR.