Assessing the contribution of gut-to-lung translocation to bacterial colonization and antibiotic resistance in an ICU patient

Bacteria have the potential to migrate between sites in the human body, but the dynamics and consequences of within-host translocation remain poorly understood. Here we investigate the link between gut and lung Pseudomonas aeruginosa populations in an intensively sampled ICU patient using a combination of genomics, isolate phenotyping, host immunity profiling, and clinical data. Crucially, we show that lung colonization was driven by the repeated translocation of bacterial clones from the gut. Meropenem treatment for a suspected urinary tract infection selected for elevated resistance in both the gut and lung. However, resistance was driven by parallel evolution and organ-specific selective pressures, and within-host transmission had only a minor impact on AMR. These findings suggest that reducing intestinal colonization of Pseudomonas may be an effective way to prevent lung infections in critically ill patients.