How does the gut microbiome recover after diarrhea?

 Scanning electron microscope image of  Vibrio cholerae , the cause of cholera and a major cause of diarrhea-associated deaths each year.

Scanning electron microscope image of Vibrio cholerae, the cause of cholera and a major cause of diarrhea-associated deaths each year.

Diarrhea is an important global health challenge that kills nearly two million people each year.  Even when it is not lethal it can have important detrimental impacts, especially on children.  For example, frequent diarrhea is associated with decreases in height, IQ, and heart health.  Diarrhea is frequently a microbiome – based disorder, and gut pathogens like enterotoxin producing Escherichia coli and Vibrio cholerae are often the culprits.  Using diarrhea caused by these pathogens as their model, scientists from Harvard University recently studied how the gut microbiome rebounds after diarrhea.  They published their results in Mbio.

The scientists measured the stools of 41 people (both children and adults) in Bangladesh that had diarrhea caused by E. coli or V. cholerae (the cause of cholera).  They measured the patients’ stools before, during, and after their diarrhea episodes and tracked the changes that occurred in all patients’ stools.  Interestingly, they identified a consistent succession of the gut microbiome that occurred in nearly all cases, regardless of the cause of diarrhea.  First, the diarrhea (or antibiotic treatment for the diarrhea) clears out much of the microbiome, and leaves both carbohydrates and oxygen to accumulate in the gut.  (Carbohydrates and oxygen would normally be metabolized by the microbiome, but in the absence of many bacteria, these things accumulate.)  Next, oxygen respiring and carbohydrate utilizing bacteria (especially those using simple carbs) colonize the gut and decrease the abundance of both of these substrates.  After, the lack of simple sugars and oxygen leads to a decline in the population of bacteria that use these, and the succession to anaerobic (i.e. do not respire oxygen), complex carb fermenting bacteria begins.  Finally, the gut microbiome resembles the complex community that existed prior to infection and the onset of diarrhea.  The entire process takes about 30 days to complete, but depends on a variety of factors such as diet, antibiotic use, and duration of diarrhea.

Studies like this one are important to combatting diarrhea, and shortening recovery time.  For example, it is now known that oxygen accumulates after diarrhea, and that while it exists at high levels the microbiome is not fully recovered.  Perhaps introducing an agent after diarrhea that rapidly decreases the amount of oxygen in the terminal gut could hasten the microbiome recovery time and improve the patient’s wellbeing.  Next time you have diarrhea, remember that it takes almost a month for your microbiome to recover, so nurture during that time.

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