Adaptability of Small Bowel Bacterial Populations

​Traditionally it has been difficult for researches to study bacterial population changes in the small bowel, as they are only reachable during surgery or endoscopy.  Now, researchers led by Andrew Macpherson and Bahtiyar Yilmaz from the Department for Biomedical Research at the University of Bern and the University Clinic for Visceral Surgery and Medicine at the Inselspital have used patients with ileal ostomies as a means to survey the small bowel microbiome in real-time, leading to some interesting discoveries. 
 
Among the findings, ileal bacteria populations are highly variable, largely disappearing when individuals fast while sleeping overnight, only to bloom again when food is consumed at breakfast.  Interestingly, while the number of bacteria fluctuates significantly, the types of bacteria that comprise the microbiome do not.  The changes that occur in the bacterial populations also happen quickly, within hours of consuming a meal.  This differs from the bacteria in the large bowel, whose numbers and proportions remain stable.
 
The head of the study and its senior author, Andrew Macpherson, stated that "Because the system is so flexible, each bacterial species can adapt to a changing environment in the small intestine by changing the proportions of subspecies and thus prevent the species as a whole from dying out." As a result the ileal bacteria normally avoid species extinctions, unless there is an illness, malnutrition, or other environmental factor. 
 
These findings, and the use of small bowel ostomies as a research tool, will enable further research into the interaction of the small intestine microbiome and diseases like Crohn’s, Colitis, and celiac.  
 
(Plasticity of the Adult Human Small Intestinal Stoma Microbiota. Cell Host & Microbe, 2022; DOI: 10.1016/j.chom.2022.10.002).