Survival of E. faecium cells following exposure to 0.3% bile salts with and without pre-adaptation. Exponential-phase cells of the E1162 wild type, the ΔgltK mutant and its in trans complemented strain ΔgltK+gltK were adapted to 0.02% bile salts for 15 min or were left unadapted, and then challenged with 0.3% bile salts. Viable cells were determined immediately before exposure to 0.3% bile salts (t = 0 min) and after 5, 30 and 60 min of challenge. The grey line represents unadapted cultures of these strains, in which viable counts dropped to undetectable levels (<50 CFU/ml) after being challenged by bile salts. Bars represent the standard deviation of the mean of three independent experiments. Asterisks represent significant differences (*: P<0.05, **: P<0.01, as determined by an unpaired two-tailed Student’s t-test) between the ΔgltK mutant and the wild type strain.