Pyocyanin produced by Pseudomonas aeruginosa creates legacy effects that promote antibiotic resistance evolution in enterococci.

Polymicrobial infections are small communities of multiple interacting bacterial species. Interactions among constituent species may modify the growth of community members in the presence of antibiotics, for example, via degradation of the antibiotic, the induction of specific resistance mechanisms, or increased mutation supply rates. However, for most polymicrobial infections, the nature of such interactions is opaque, while they may affect both treatment efficacy and the evolution of antibiotic resistance. Here, we describe that past interaction of enterococci with Pseudomonas aeruginosa creates legacy effects that substantially enhance their antibiotic tolerance and promote resistance evolution. Specifically, we find that the temporary exposure to pyocyanin, a secondary metabolite produced by P. aeruginosa, increases antibiotic efflux in enterococci. We show that these tolerance legacy effects enhance the tolerance to rifampicin and nalidixic acid, and thereby promote the evolution of antibiotic resistance of enterococci. This work shows that transient interactions in polymicrobial communities can alter the evolutionary fate of community members.