One well-described example of cooperative virulence is provided by Salmonella enterica serovar Typhimurium (S. Typhimurium), a gastrointestinal pathogen whose Salmonella pathogenicity island 1 (SPI-1) type 3 secretion system (T3SS) elicits a proinflammatory host response that is necessary for S. Typhimurium to overcome colonization resistance and establish infection in the gut (7). This evidence concerns the gene SPI1 and infection.