KLK4 and digestive system infectious disorder: The importance of PstS in in vivo virulence has been previously addressed in various models including a mouse infection model using Mycobacterium tuberculosis and pstS1 and pstS2 knockout strains [55], a fish infection model using Edwardsiella tarda, a facultative aerobic enterobacterium that causes hemorrhagic septicemia in fish and gastrointestinal infections in humans [56], and a chicken infection model using Escherichia coli O78, an organism associated with extraintestinal infections and septicemia in poultry, livestock, and humans [57].