The host-associated microbial community can provide protection against invading pathogens. However, whether adaptive evolutionary changes in these resident microbial communities affect invasion resistance is not well understood. In this study, Muzafar et al. determined the impact of adaptive changes in synthetic microbial communities on the invasion of an Escherichia coli strain with a virulent phenotype. The authors performed experimental evolution on communities of E. coli and Salmonella enterica ser. Typhimurium. They reported that the evolved clones of E. coli and S. Typhimurium exhibited increased fitness compared with their respective ancestors, and had mutations in genes involved in carbon metabolism, motility and adhesion. The authors also found that, compared with ancestral communities, the evolved communities were less resistant to invasion by an E. coli strain that produces colicin toxin. Finally, the authors showed that the observed decrease in invasion resistance was linked to enhanced interspecific competition and ecological specialization in the community. In summary, the study provides insights into how adaptive changes in evolved microbial communities can affect pathogen invasion.