During the study, each of the two subjects experienced an event that dramatically altered the gut microbiome. Subject B experienced food poisoning caused by Salmonella, and Subject A traveled to a developing nation, where he experienced diarrheal illness for two weeks.
During Subject B's infection, Salmonella leapt from 10 percent of the gut microbiome to nearly 30 percent. At the same time, populations of bacteria from the phylum Firmicutes, believed to be beneficial to human health, nearly disappeared. After the subject recovered, Firmicutes rebounded to about 40 percent of the total microbiome, but most of the strains were different from those originally present.
"There really wasn't an overall change in the level of Firmicutes. The levels are very different from person to person, but whatever it is about a person that is maintaining a certain level is able to survive a huge insult like that. What's keeping it at that level is a really interesting research question," Alm says, adding that the answer may lie in dietary differences.
Subject A also exhibited severe disruptions to his microbiome during his trip, but once he returned to the United States, it returned to normal. Unlike Subject B's recovery from food poisoning, Subject A's populations returned to their original composition.
The researchers now plan to investigate why microbiome populations tend to return to an average value, specific to the individual host, after going way up or down. They also plan to study how the immune system responds to changes in the microbiome by measuring daily changes in cytokine and hormone levels. To make such follow-u
|Contact: Sarah McDonnell|
Massachusetts Institute of Technology