International travel is part of modern life, your life. Whether that is visiting family in Europe, business trips to Asia, or a dream vacation to the tropics, these all have something in common. The microbes and germs in these places are different and not what your body is used to at home.
Your body is covered, inside and out, with little microbes that influence your health both mentally and physically (Beaumont et al. 2018. Hathaway et al. 2021). These symbionts (organisms that coexist and interact closely with another organism) are not the same for every person, especially at a global scale. Recent advancements in global sampling of microorganisms has shown that novel and unknown microbes are not only common in the cities of the world but often differ based on the climate, country, and various other environmental factors. Consequently, when a person travels to a new part of the globe, they are exposed to microbes that their bodies may never have seen before and contact with microbes like these can lead to some uncomfortable conditions (Danko et al. 2021).
If these unusual and disrupting bacteria get a foothold in your gut microbiome, then you could experience sickness such as traveler’s diarrhea , and other illnesses caused by imbalances in the gut microbiome (Connor et al. 2020).
A team of scientists in Ireland, Ciara M. O’ Donovan, Brendan Connor, Sharon M. Madigan, Paul D. Cotter, and Orla O’ Sullivan teamed up with the Ireland Cricket team to see if traveling around the globe might induce changes in the human gut microbiome (Connor et al. 2020).
This study, Instances of altered gut microbiomes among Irish cricketers over periods of travel in the lead up to the 2016 World Cup: A sequencing analysis, was conducted to determine if there was a connection between the microbiome of the gut undergoing alterations and traveling.
Considering the question, these athletes fill the role of travelers perfectly. International sports teams are constantly engaged in tours and tournaments world wide while often returning to their home country for matches. A baseline of their gut microbiome was set in their home country of Ireland prior to the start of the sporting season (Connor et al. 2020). This particular sport team, Mens Cricket Ireland, then had fecal samples taken in Ireland before and after each subsequent trip allowing researchers to track how the microbiome in individual players responded to each period of travel. By sampling after multiple trips, this study managed to expand their inquisition on this topic.
The four players of interest had shotgun metagenomic sequences (a genomic identification strategy that analyzes many different microbial cells at the same time) taken from each of their stool samples collected over time. This kind of analysis creates the opportunity for researchers to more than just identify what microbes are present but also to discover the potential functions in the microbiome.
If microbiome disturbance is rare enough, a single trip made by these athletes may have not identified any relevant information on disturbance to their gut microbiomes; however, following individuals over the start of a season, the beginning of the world cup of 2016, to multiple countries created an in depth study. In reference to figure 1 from this study, we see that players gut microbiome similarity between when they started their journey and ended it after five tours. While some players are not heavily affected, the researchers saw that 2 of the players experienced heavy alterations to their microbial profiles after travel (Connor et al. 2020). Once it became clear travel could have an altering effect on traveler’s microbiomes , the researchers were also able to identify specific microbe fluctuations seen in figure 2. These players, players 2 and 11, saw increased numbers of microbes that were not previously present in the players microbiomes.
After travel to India, there were 6 particular microbiota that exploded in population size since the baseline stool sampling (Connor et al. 2020). These were identified as being biomarkers (microbes present in only specific circumstances) to those players experiencing gastrointestinal discomfort after their trip to India.
Zambia/Nambia, Ireland, Australia, the United Arab Emirates, and India let researchers identify where and when alterations in player’s microbiome health changed (Connor et al. 2020). In figure 2, researchers conducted a LEfSE analysis and found certain genera that displayed associative pairing with time point locations. The presence of previously non-existent microbiota appeared in the post India travel time (Connor et al. 2020). Investigation by these researchers shows that the new microbes possessed antibiotic resistant genes in higher levels than usually observed. This quality is linked to bacteria causing more inflammation than the wildtype strains (Connor et al. 2020). We can see that the researchers did find a basis for travel altering the microbiome. What is currently unclear is what exact circumstances lead to the gut microbiome alterations. Perhaps further study will shed some light on the finer points of risky behaviors during extended travel.
Is this research generalizable to the common population? These athletes are quite different to the average person in many different facets of their lives. How much they exercise, what they eat, and most importantly how often they are traveling internationally. Perhaps the frequency and duration of their stays in foreign countries played a role. The players spent 30 days within India alone (Connor et al. 2020).
Why are antibiotic resistant bacteria making successful colonization of players’ microbiomes over other non-resistant species? Is this a bad thing? The researchers in Connor et al. note that the chances of getting antimicrobial resistant bacteria increase due to a couple factors. The main one being using antibiotics just prior to or during travel (Connor et al. 2020). This reduces the initial population of microbes in the gut, then while the antibiotics are still present in a person’s body, the antibiotic resistant strains are more likely to be able to survive the conditions of the gut. Usually these types of strains are pathonogentic because we target those kinds of bacteria with antibiotics leading to resistance. These then persist causing inflammation and other problems in the person’s gut (Yujie et al. 2019).
In this cricket player analysis, the researchers did observe alterations in gut microbiome health but perhaps more surprisingly, the changes came with a slew of antibiotic resistant bacteria. This connection is no longer novel and has been observed in other studies including here (Danko et al. 2021).
The use of antibiotics does not end within our bodies either, as disposal of these drugs is far from efficient. Amounts of antibiotics are being found in sewage and water treatment plants which creates a selective pressure on bacteria in our surrounding environments to possess antibiotic resistant genes (Yujie et al. 2019).
The degree of physical robustness has been linked strongly to a healthy gut microbiome (Beaumont et al.). These researchers wanted to discover if there was a connection between mental health problems in aged populations and their gut microbiomes. A problem discovered by the researchers was in dissociating their subjects’ physical health from their mental health. The interconnectedness of the subjects gut microbiomes and physical health suggested that physical and mental health are also connected.
Beaumont M., Bell J. T., Bowyer R., Jackson M.A., Spector T.D., Steves C.J. Verdi S. An Investigation Into Physical Frailty as a Link Between the Gut Microbiome and Cognitive Health. Frontiers in Aging Neuroscience. Vol 10, 2018, pp. 398, ISSN=1663-4365, DOI=10.3389/fnagi.2018.00398
Connor, B., Cotter, P.D., Madigan, S.M., O’Donovan, C., O’Sullivan, O. Instances of altered gut microbiomes among Irish cricketers over periods of travel in the lead up to the 2016 World Cup: A sequencing analysis,Travel Medicine and Infectious Disease, Volume 35, 2020, ISSN 1477-8939, DOI=10.1016/j.tmaid.2020.101553.
Danko, David, Daniela Bezdan, Evan E. Afshin, Sofia Ahsanuddin, Chandrima Bhattacharya, Daniel J. Butler, Kern Rei Chng, Daisy Donnellan, Jochen Hecht, Katelyn Jackson, Katerina Kuchin, Mikhail Karasikov, Abigail Lyons, Lauren Mak, Dmitry Meleshko, Harun Mustafa, Beth Mutai, Russell Y. Neches, Amanda Ng, Olga Nikolayeva, Tatyana Nikolayeva, Eileen Png, Krista A. Ryon. A global metagenomic map of urban microbiomes and antimicrobial resistance, Cell, Vol 184, 13, 2021, pp. 3376-3393, ISSN 0092-8674, DOI=10.1016/j.cell.2021.05.002.
Hathaway H., Jeste D., Knight R., Kosciolek T., Nguyen T.T. Gut microbiome in serious mental illnesses: A systematic review and critical evaluation, Schizophrenia Research, Vol 234, 2021, pp. 24-40, ISSN 0920-9964, DOI=10.1016/j.schres.2019.08.026.
Yujie Ben, Caixia Fu, Min Hu, Lei Liu, Ming Hung Wong, Chunmiao Zheng, Human health risk assessment of antibiotic resistance associated with antibiotic residues in the environment: A review, Environmental Research, Vol 169, 2019, Pages 483-493, ISSN 0013-9351, DOI=10.1016/j.envres.2018.11.040.