Live Cell Methods to Visualize Translocated Salmonella Effectors and Monitor Ca2+ Transients During Infection

Salmonella species invade and survive within eukaryotic host cells by using a Type Three Secretion System (T3SS) to translocate bacterial effector proteins into the host cell and commandeer host-cell signaling processes, including Ca2+ regulation. T3SS effector activity is tightly regulated, in part by their different spatial distribution within the host cell, to coordinate each stage of the infection process. To date, more than 40 T3SS effector proteins have been identified, but their biochemical functions and role in the infection process are often poorly understood. Complexity of effector regulation coupled with growing evidence for cell-to-cell heterogeneity of infection underscores the importance of being able to localize and monitor effectors directly in living infected host cells. However, progress in understanding the dynamics of when and where effectors localize within host cells has been challenging due to limited tools to study these proteins in the native cellular environment throughout the course of infection. Here we discuss two novel imaging methods, one was created to study the host cell localization of specific effector proteins and the other to monitor host cell Ca2+ transients that occur upon Salmonella internalization