Figure 1: Host survival showing protective effects of E. faecalis . Early exposure of worms toE. faecalis (both ancestors) provides some degree of protection from the infection of S. aureus . 24h host survival levels reveal a benefit to E. faecalis colonisation independent of pathogen presence or absence. Circles indicate those treatment being exposed toE. faecalis and food in the earlier stage (L1-L4), while squares indicate food alone treatment in the earlier stage (L1-L4). Filled symbols indicate those treatments being exposed to food in the later stage, while open symbols indicate those treatments being exposed to the pathogen S. aureus in the later stage. Each symbol indicates the mean ± S.E of five replicates. Axis scales were chosen to be the same across all plots.

Before the start of the evolution experiment, the starting conditions were tested. Confirming previous results, E. faecalis showed some spontaneous host-protective potential against S. aureus . Worms raised on E. faecalis and food survived better than those raised on food alone, independent of food or pathogen present at the later stage (General Linear Model, X²=10.205, df=1, p=0.001; Figure 1). Worms infected with S. aureus in later life survived worse than those being exposed to food (General Linear Model, X²=119.643, df=1, p<0.001; Figure 1). These results demonstrate the beneficial and protective effects for the host after exposure to the protective microbe E. faecalis .