Answer by Tirumalai Kamala:
A recent peer-reviewed study () suggests that travel can temporarily change gut microbiota, that such a change reverts to pre-travel state once travel is done. Enteric (gut) infection, on the other hand, appears to create a competitive environment where pre-infection species could be replaced by closely related ones.
The study followed two male volunteers for one year: “349 health and lifestyle variables spanning fitness, diet, exercise, bowel movements, mood, and illness“. “Each day, subjects were asked to collect stool and saliva samples in order to measure the dynamics of gut and oral microbial communities“.
They report “Travel and enteric infection are associated with profound community disturbance”.
Travel-associated microbial community disruption. Subject A relocated from “a major American metropolitan area to the capital of a developing nation in Southeast Asia between days 71 and 122 of the study”. “had diarrhea on days 80 to 85 and 104 to 113”.
Travel-associated disruption in Subject A was temporary and reverted back to pre-travel microbiota within 14 days of return. Authors call this the environmental disturbance model of microbiome state transition. Temporary shift in microbial composition in terms of species reverted back once travel-associated disruption ended.
Food poisoning-associated microbial community disruption. Subject B had an episode of food poisoning, “during which the subject tested culture positive for Salmonella sp. Consistent with this diagnosis, reads from the Enterobacteriaceae (Salmonella’s parent family) accounted for a median of 10.1% of daily reads during the diarrheal illness and peaked at 29.3% of reads on day 159”.
Infection-associated disruption in Subject B did not revert back to pre-infection state during the remaining 3 months of follow-up. Authors call this the community disturbance model. There was a shift in microbial composition in terms of species, while functional stability was maintained. How so? Pre-infection species were replaced by closely related ones. Infection-associated gut microbiota changes suggests two things:
- That disruption caused by pathogenic microbes creates de novo competition among closely related gut commensals.
- Pre-infection gut commensal residents may not necessarily win such a competition.
Caveats to the study:
- Too few subjects. Only two, both male.
- Only one method of assessment, 16S ribosomal RNA. Too sensitive. Requires normalization, which in turn creates artifacts. Cannot distinguish stable inhabitant from microbes passing through. Sweet-spot methodology would be one that combined 16S ribosomal RNA with microbial cultures. Problem is we don’t know how to culture the majority of microbes that inhabit our body.
- Only examined stool and saliva (ended up having saliva data from only one subject).