SPI1 and Salmonella Infections: However, the choice of host species alters Salmonella infection strategies, and it was previously shown that the SPI-1 T3SS is not required for S. Typhimurium invasion into our highly differentiated 3-D HT-29 colon models [29], [30], which is in agreement with studies reporting that SPI-1 is not required to cause enteropathogenesis in vivo[47]–[52].