Fig. 3: Bacteriocin T8 production provides a competitive advantage in vitro and increases E. faecium colonization and competition in vivo.

a, Pairwise spot killing assay of strains pBAC, carrying bacteriocin T8 and the corresponding immunity gene, and pEV, carrying an empty vector. The dashed circle shows where the pEV strain was spotted onto the pBAC strain lawn but did not grow. b, Liquid competition assay. The pBAC and pEV strains were independently competed against the parent strain at 50:50 and 10:90 ratios. Samples were taken after 24 h and 48 h to calculate CFU ml⁻¹. Assays were performed in three biological replicates each consisting of three technical replicates. Instances in which the parent strain fell below the limit of detection (LOD, shown with the grey dashed line) were not included in statistical analyses. Competitive indexes were summarized using the geometric mean and a 95% confidence interval (error bars) for each timepoint and ratio⁷⁰. The distribution of competitive index values at each timepoint and ratio was compared between pBAC and pEV strains using a two-tailed Mann–Whitney test (adjusted, *P < 0.005, **P < 0.001); 50:50 24 h (P = 0.0028), 50:50 48 h (P = 0.0002), 10:90 24 h (P = 0.0008) and 10:90 48 h (P = 0.0004). Black dashed line corresponds to a competitive index of 1.0. c, Colonization of pBAC and pEV strains in the mouse gut. Mice were orally gavaged with either the pBAC (n = 10) or pEV (n = 10) strain for 2 days. Stool samples were collected starting on day 1 after the initiation of infection to quantify CFU g⁻¹ of each strain over time. Data were summarized using the mean with error bars representing standard error measurement. A two-tailed multiple Mann–Whitney test was used and assessed CFU g⁻¹ distribution between pBAC and pEV strains (adjusted, *P < 0.05; NS, non-significant); day 1 (P = 0.6839), day 2 (P = 0.0230), day 3 (P = 0.0084), day 4 (P = 0.0026), day 5 (P = 0.0120), day 6 (P = 0.0410), day 7 (P = 0.0001) and day 8 (P = 0.0061). d, Competition between a bacteriocin T8-positive ST117 strain and a bacteriocin T8-negative ST17 strain within the mouse gut. Data show the percentages of ST117 in the inoculum on day 0 and at 4 days postinfection. Proportions of ST117 on day 4 and in the inoculum for each animal were compared using a one-sided difference in proportion hypothesis test (adjusted, ***P ≤ 0.0001) for each mouse.