LAKE TAHOE, CALIF. – according to Mark A. Underwood, MD.
Doug Brunk/MDedge News
Dr. Mark A. Underwood
“Antibiotic exposure changes the composition of the intestinal microbiota,” he said at the annual meeting of the Society for Pediatric Dermatology. “That clearly causes both antibiotic-associated diarrhea and Clostridium difficile colitis. The bigger question is, is it possible that intestinal dysbiosis is related to a whole bunch of other systemic diseases? In other words, does an insult during a critical window of development cause changes in the intestinal microbiota that can lead to systemic diseases in the brain, the lung, the liver, or the immune system?”
According Dr. Underwood, a pediatrician who is chief of the division of neonatology at the University of California, Davis, the prevalence of dysbiosis is increasing worldwide, particularly in developed countries, where Bifidobacteria are decreasing and Enterobacteriaceae are increasing. “Those changes are associated with gut permeability and alterations in both local and systemic inflammation, and the risk for a number of diseases, including atopic dermatitis,” he said. Key reasons for the increasing prevalence of dysbiosis, he continued, include the use of antibiotics, cesarean section delivery, formula feeding, changes in hygiene that alter the intestinal biota, the high-fat, high-sugar Western diet, and a loss of vertical and horizontal transmission over generations.
In a study of 44 term infants with a family history of allergy, changes in the fecal microbiota, especially colonization with Ruminococcus gnavus, preceded the onset of allergic symptoms (Gastroenterol. 2018;154[1]:154-67). The same researchers observed similar findings in an animal model.
One potential mechanism by which intestinal dysbiosis causes systemic disease is stimulation of toll-like receptor 4 (TLR4), “which is a receptor on a variety of mucosal cells that senses the presence of a microbial pathogen-associated patterns, particularly those of Gram-negative Enterobacteriaceae,” Dr. Underwood explained. Other potential mechanisms include increased intestinal permeability, an increase in the pH and decreases in short-chain fatty acids within the gut lumen, and a loss of intraluminal hypoxia. “Think of the colon as an anaerobic chamber,” he said. “The colon lumen should be very low in oxygen. It should be dominated by obligate anaerobes.”
Efforts to prevent or treat dysbiosis-related diseases include the use of probiotics and fecal transplantation. A recent Cochrane review of 8,672 patients found “moderate certainty evidence” that probiotics are effective for preventing C. difficile-associated diarrhea. The analysis included 31 randomized, controlled trials of adults who were treated either with a probiotic or with a placebo. When pooled, the risk ratio was 0.40, which represented a significant protection. In addition, a summary of 7 randomized controlled trials and 30 case series suggests that fecal microbial transplantation is superior to vancomycin for adults with recurrent C. difficile colitis (relative risk 0.23) (Aliment Pharmacol Ther. 2017;46[5]:470-93).
To date, the effect of giving probiotics to pregnant women who have a family history of allergy is less clear. One pooled analysis of such studies put the overall risk ratio at 0.74 (Mil Med. 2014;179[6]:580-92). “While I think the jury’s still out on how to best prevent atopic dermatitis in these families, it looks like there is some potential benefit in treating these moms during pregnancy with probiotics and treating the infant during the first few months of life,” Dr. Underwood said. The most effective were mixtures including one or more Lactobacillus species or L. rhamnosus, mixtures including one or more Bifidobacterium species, or B. lactis by itself. The use of probiotics also has been found to prevent necrotizing enterocolitis, sepsis, and death in premature infants (Semin Pediatr Surg. 2018;27[1]:39-46).
Dr. Underwood disclosed that he has received honoraria from Abbott and that he was a member of the scientific review board for Avexegen. He also chaired the data safety and monitoring board for Infant Bacterial Therapeutics and has received support from Evolve BioSystems to perform a clinical trial.