A new paradigm of bacteria-gut interplay brought through the study of Shigella

Bacteria-gut epithelial interplay and the mucosal immune response are the most critical issues in determining the fate of bacterial infection and the severity of diseases. Shigella species (abbreviated here as Shigella), the causative agent of bacillary dysentery (shigellosis), are highly adapted human pathogens that are capable of invading and colonizing the intestinal epithelium, which results in severe inflammatory colitis. Shigella secrete a large and diverse number (more then 50) of effectors via the type III secretion system (TTSS) during infection, some of which are delivered into the surrounding bacterial space and some others into the host cell cytoplasm and nucleus. The delivered effectors mimic and usurp the host cellular functions, and modulate host cell signaling and immune response, thus playing pivotal roles in promoting bacterial infection and circumventing host defense systems. This article overviews the pathogenic characteristics of Shigella, and highlights current topics related to the bacterial infectious stratagem executed by the TTSS-secreted effectors. Though bacterial stratagems and the molecular mechanisms of infection vary greatly among pathogens, the current studies of Shigella provide a paradigm shift in bacterial pathogenesis.