Enteropathogenic bacteria are causing numerous diarrheal infections and they provide excellent models for basic research in immunology, microbiology and evolution. I will report on our work on Salmonella diarrhea using mouse colonization and disease models. The lecture will review recent advances in our understanding of the pathogen's growth physiology in the mammalian gut, its interactions with the microbiota and how it elicits the host's immune defenses. Then, I will present our current work on the spread of antibiotic resistance plasmids and how these selfish genetic elements are subverting the pathogen and the host for spreading efficiently in microbial communities. Deciphering the underlying mechanisms may help to devise strategies for fighting the antibiotic resistance crisis.