Background Antimicrobial resistance (AMR) is highly prevalent in low- and middle-income countries (LMIC). International travel contributes substantially to the global spread of intestinal multidrug-resistant gram-negative (MDR-GN) bacteria. Of the 100 million annual visitors to LMIC, 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. We aimed to characterize colonization dynamics by exploring stool samples abroad on a daily basis while visiting LMIC.Methods 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.Results 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 colonization 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 (n=2–7). Of the total of 83 unique strains identified (53 E. coli , 10 Klebsiella , 20 other ESBL-GN species), some were shared by as many as four subjects.Conclusions 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.*   AMR    :   Antimicrobial resistance    DEC    :   diarrheagenic Escherichia coli     ESBL    :   extended-spectrum beta-lactamase    ESBL-Ec    :   extended-spectrum beta-lactamase (ESBL)-producing E. coli     ESBL-GN    :   extended-spectrum beta-lactamase-producing gram-negative bacteria    ESBL-PE    :   extended-spectrum beta-lactamase-producing Enterobacteriaceae     IQR    :   inter quartile range    Laos    :   Lao People’s Democratic Republic People’s Democratic Republic    LMIC    :   low- and middle-income countries    mcr    :   mobile colistin resistance genes    MDR    :   multidrug-resistant    MDR-GN    :   multidrug-resistant gram-negative bacteria    TD    :   travelers’ diarrhea    WGS    :   whole-genome sequencing

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