To study how flies deal with infections in a natural context, we investigated the interactions between Drosophila and a newly identified entomopathogen, P. entomophila. Using a combined genetic approach for both the host and pathogen we reveal the importance of the local immune response in host defense against gastrointestinal infections and provide an in vivo demonstration for the role of a bacterial metalloprotease in protection against AMPs. The gene discussed is ADSL; the disease is digestive system infectious disorder.