SPI1 and infection: Subsequent work demonstrated that all characterized S. Typhimurium T3SSs (SPI-1, SPI-2, and the flagellar pore) are dispensable for Salmonella invasion into highly differentiated 3-D HT-29 cells, but are required for intracellular bacterial growth, paralleling in vivo infection observations and demonstrating the utility of these models in predicting in vivo-like pathogenic mechanisms and for studying host-microbe interactions [30].