Figure 5. Ampicillin treatment promotes VRE intestinal colonization in mice.

(A) The number of VRE CFUs in the small intestine or cecum of untreated mice, mice treated for 1 week with ampicillin before infection and kept on ampicillin after VRE infection, or mice switched back to antibiotic-free water 1 day after infection and allowed to recover. Mice were infected with 10⁸ CFUs. Samples were harvested on different days after VRE infection. n ≥ 6 mice per group and day, except day 15 ampicillin (n = 3). (B) Phylogenetic classification of 16S rDNA frequencies or (C) number of 16s rDNA copies in the ileum and cecum of untreated mice as well as ampicillin-treated mice, infected or not with VRE after 1 week of treatment, and either treated for 8 days or allowed to recover starting at 1 day after infection. The most predominant bacterial populations identified are color coded as indicated. Each bar represents the microbiota composition of an individual mouse.