Within-host density and duration of colonization of multidrug-resistant Enterobacterales acquired during travel to the tropics

Although it seems obvious that antibiotic use promotes antibiotic resistance, the processes underlying the changes in prevalence of MRE in European communities are still poorly understood. Information on how the within-host bacterial density varies after acquisition of a resistant strain and in the absence of antibiotic selection is key to our ability to further understand, model and manage resistance in the community. Empirical studies on the within-host dynamics following colonization by MRE are very scarce. Here, we study the within-host strain dynamics in healthy travelers colonized with MRE upon their return from tropical regions. Densities of both sensitive and resistant strains are stable for a few months, until resistant strains are abruptly cleared. Multivariate survival analysis further revealed that MRE acquired from Asia and carried at larger densities persist for longer. These dynamics do not support the classically assumed slow competitive exclusion of MRE. Rather, MRE and sensitive strains coexist in apparent equilibrium for months, with MRE representing about 0.1% of total Enterobacterales, before MRE are abruptly cleared. These results inform potential therapeutic strategies to clear MRE and epidemiological models of antibiotic resistance. ### Competing Interest Statement The authors have declared no competing interest.