Shigella sonneiis a bacterial pathogen and causative agent of bacillary dysentery. It deploys a type III secretion system to inject effector proteins into host epithelial cells and macrophages, an essential step for tissue invasion and immune evasion. Although the arsenal of bacterial effectors and their cellular targets have been studied extensively, little is known about the prerequisites for deployment of type III secreted proteins during infection. Here, we describe a novelS. sonneiadhesin, SSO1327 which is a multivalent adhesion molecule (MAM) required for invasion of epithelial cells and macrophages and for infectionin vivo. TheS. sonneiMAM mediates intimate attachment to host cells, which is required for efficient translocation of type III effectors into host cells. SSO1327 is non-redundant to IcsA; its activity is independent of type III secretion. In contrast to the up-regulation of IcsA-dependent and independent attachment and invasion by deoxycholate inShigella flexneri, deoxycholate negatively regulates IcsA and MAM inS. sonneiresulting in reduction in attachment and invasion and virulence attenuationin vivo. A strain deficient for SSO1327 is avirulentin vivo, but still elicits a host immune response.
A novel S. sonnei adhesion of the Multivalent Adhesion Molecule (MAM) family is identified. Removal of MAM gene severely attenuated virulence in Galleria moth larvae and guinea pig eye keratoconjunctivitis models. MAM mediates intimate attachment to host cells, which is required for efficient translocation of type III effectors into host cells. As little as 6 μM synthetic beads coated with MAM protein can completely prevent S. sonnei killing of the moth larvae.