ObjectiveInfections caused by multidrug-resistant Gram-negative bacilli (MDR-GNB) are a major issue in intensive care. The intestinal and oropharyngeal microbiota being the reservoir of MDR-GNB. Our main objective was to assess the link between the composition of the intestinal and tracheal microbiota and colonization by MDR-GNB. MethodsWe performed a 2-month prospective, monocentric cohort study in the medical intensive care unit of our hospital. Patients ventilated >3 days and spontaneously passing faeces were included. A faecal sample and an endotracheal aspiration (EA) were collected twice a week. MDR-GNB but also Enterococcus faecium and yeasts (as potential dysbiosis surrogate markers) were detected by culture methods. The composition of the intestinal and tracheal microbiota was assessed by 16S profiling. ResultsWe collected 62 couples of faeces and EA from 31 patients, including 18 faeces and 9 EA positive for MDR-GNB. We did not observe a link between the diversity and the richness of the intestinal microbiota and the MDR-GNB intestinal relative abundance (RA). Conversely, we observed a negative link between the intestinal diversity and richness and the RA of Enterococcus spp. (p<0.001). ConclusionThe intestinal MDR-GNB RA was not associated to the diversity nor the richness of the intestinal microbiota, but that of Enterococcus spp. was.