Shigella spp. are transmitted by the fecal-oral route and enter the human body via the ingestion of contaminated food or water. The bacteria are highly infectious, since as few as 10 to 100 microorganisms are sufficient to cause disease (61). This low infectious dose can at least partially be attributed to the presence of effective acid resistance systems, which enable S. flexneri to survive the acidic environment in the stomach (88). Furthermore, it was shown that Shigella spp. are able to downregulate the expression of antimicrobial peptides, which are important antibacterial effectors constantly released from the mucosal surfaces of the intestinal tract (118). After passage through the stomach and small intestine, the bacteria reach the large intestine, where they establish an infection.