Real-time sampling of travelers shows intestinal colonization by multidrug-resistant bacteria to be a dynamic process with multiple transient acquisitions

<jats:title>Abstract</jats:title><jats:sec><jats:title>Background</jats:title><jats:p>Antimicrobial resistance (AMR) is highly prevalent in low- and middle-income countries. International travel contributes substantially to the global spread of intestinal multidrug-resistant gram-negative (MDR-GN) bacteria. Of the 100 million annual visitors to tropical countries, 30–70% become colonized by MDR-GN bacteria. The phenomenon has been well documented, but since sampling has only been conducted after travelers’ return home, data on the actual colonization process are scarce.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>A group of 20 European volunteers visiting Lao People’s Democratic Republic for three weeks provided daily stool samples and filled in daily questionnaires. Acquisition of extended-spectrum beta-lactamase-producing gram-negative bacteria (ESBL-GN) was examined by selective stool cultures followed by whole-genome sequencing (WGS) of isolates.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>While colonization rates were 70% at the end of the study, daily sampling revealed that all participants had acquired ESBL-GN at some time point during their overseas stay, the status varying day by day. WGS analysis ascribed the transient pattern of colonization to sequential acquisition of new strains, resulting in a loss of detectable colonization by the initial MDR-GN strains. All but one participant acquired multiple strains (2–5). Of the total of 83 unique strains identified (53 <jats:italic>E. coli</jats:italic>, 10 <jats:italic>Klebsiella</jats:italic>, 20 other ESBL-GN species), some were shared by as many as four subjects.</jats:p></jats:sec><jats:sec><jats:title>Conclusions</jats:title><jats:p>This is the first study to characterize in real time the dynamics of acquiring MDR-GN during travel. Our data show multiple transient colonization events indicative of constant microbial competition.</jats:p></jats:sec><jats:sec><jats:title>Summary</jats:title><jats:p>While 14 of 20 Europeans carried multidrug-resistant bacteria at the end of their 3-week visit to Laos, whole-genome sequencing of daily stool samples revealed acquisition by all, involving multiple transient acquisitions with a potential for longer MDR-GN colonization.</jats:p></jats:sec>