Intestinal microbiota in health and disease: Role of bifidobacteria in gut homeostasis

The pool of microbes inhabiting our body is known as “microbiota” and their collective genomes as “microbiome”. The colon is the most densely populated organ in the human body, although other parts, such as the skin, vaginal mucosa, or respiratory tract, also harbour specific microbiota. This microbial community regulates some important metabolic and physiological functions of the host, and drives the maturation of the immune system in early life, contributing to its homeostasis during life. Alterations of the intestinal microbiota can occur by changes in composition (dysbiosis), function, or microbiota-host interactions and they can be directly correlated with several diseases. The only disease in which a clear causal role of a dysbiotic microbiota has been demonstrated is the case of Clostridium difficile infections. Nonetheless, alterations in composition and function of the microbiota have been associated with several gastrointestinal diseases (inflammatory bowel disease, colorectal cancer, or irritable bowel syndrome), as well as extra-intestinal pathologies, such as those affecting the liver, or the respiratory tract (e.g., allergy, bronchial asthma, and cystic fibrosis), among others. Species of Bifidobacterium genus are the normal inhabitants of a healthy human gut and alterations in number and composition of their populations is one of the most frequent features present in these diseases. The use of probiotics, including bifidobacteria strains, in preventive medicine to maintain a healthy intestinal function is well documented. Probiotics are also proposed as therapeutic agents for gastrointestinal disorders and other pathologies. The World Gastroenterology Organization recently published potential clinical applications for several probiotic formulations, in which species of lactobacilli are predominant. This review is focused on probiotic preparations containing Bifidobacterium strains, alone or in combination with other bacteria, which have been tested in human clinical studies. In spite of extensive literature on and research into this topic, the degree of scientific evidence of the effectiveness of probiotics is still insufficient in most cases. More effort need to be made to design and conduct accurate human studies demonstrating the efficacy of probiotics in the prevention, alleviation, or treatment of different pathologies.

Qualitative and quantitative analyses of the bifidobacterial microbiota in the colonic mucosa of patients with colorectal cancer, diverticulitis and inflammatory bowel disease

AIM： To characterize the bifidobacterial microbiota of the colonic mucosa in patients with colon cancer, inflammatory bowel disease or diverticulitis. METHODS： A sample of the distal colonic mucosa was taken during surgery from a total of 34 patients, twenty-one with diagnosed colorectal cancer, nine with diverticulitis and four with inflammatory bowel disease, requiring surgery for their condition. Bacterial DNA was extracted from the resected mucosal samples and bifidobacterial mucosa-associated microbiota was qualitatively and quantitatively determined by means of qualitative and quantitative PCR. RESULTS： Bifidobacteria were found in 100% of the samples from patients with diverticulitis or IBD and a 76% of those suffering colon cancer. The species B. Iongum and B. bifidum were the most widely found, followed by B. animalis, B. catenulatum and B. adolescentis. B. breve, B. dentium and B. angulatum were not detected in any sample. A significantly higher occurrence of B. Iongum was observed in patients with diverticulitis than in those with colon cancer or IBD （100%, 62% and 75%, respectively, P 〈 0.05）. Similar results were obtained for B, animalis （56%, 0% and 25%, P 〈 0.05）, while B. adolescentis was only found in the mucosa from patients with colon cancer （5 out of 21, 24%）. At the quantitative level, patients with colon cancer or IBD showed lower counts of total Bifidobacterium （4.94 and 5.91 vs 6.96 log Cells/sample, respectively, P 〈 0.05） and of the species B. longum （4.05 and 4.79 vs 6.76, P 〈 0.05） than those with diverticulitis.CONCLUSION： Aberrancies in mucosa associated microbiota are present in different intestinal diseases. This may indicate a role of the microbiota in the pathogenesis of these diseases.