SPI1 and infection: We have recently shown that infection of neonate mice allows the visualization and quantitative analysis of infected enterocytes.14 Neonate mice exhibit reduced exfoliation of infected enterocytes.15,16 Using this neonate infection model, we previously characterized the requirement of individual SPI1 T3SS effector molecules for enterocyte invasion and intracellular proliferation.17 Here, we extended this work and analyzed the role of the SPI2 T3SS during this early step in the course of the infection.