Blowing epithelial cell bubbles with GumB: ShlA-family pore-forming toxins induce blebbing and rapid cellular death in corneal epithelial cells.

Medical devices, such as contact lenses, bring bacteria in direct contact with human cells. Consequences of these host-pathogen interactions include the alteration of mammalian cell surface architecture and induction of cellular death that renders tissues more susceptible to infection. Gram-negative bacteria known to induce cellular blebbing by mammalian cells, Pseudomonas and Vibrio species, do so through a type III secretion system-dependent mechanism. This study demonstrates that a subset of bacteria from the Enterobacteriaceae bacterial family induce cellular death and membrane blebs in a variety of cell types via a type V secretion-system dependent mechanism. Here, we report that ShlA-family cytolysins from Proteus mirabilis and Serratia marcescens were required to induce membrane blebbling and cell death. Blebbing and cellular death were blocked by an antioxidant and RIP-1 and MLKL inhibitors, implicating necroptosis in the observed phenotypes. Additional genetic studies determined that an IgaA family stress-response protein, GumB, was necessary to induce blebs. Data supported a model where GumB and shlBA are in a regulatory circuit through the Rcs stress response phosphorelay system required for bleb formation and pathogenesis in an invertebrate model of infection and proliferation in a phagocytic cell line. This study introduces GumB as a regulator of S. marcescens host-pathogen interactions and demonstrates a common type V secretion system-dependent mechanism by which bacteria elicit surface morphological changes on mammalian cells. This type V secretion-system mechanism likely contributes bacterial damage to the corneal epithelial layer, and enables access to deeper parts of the tissue that are more susceptible to infection. Author summary Bacteria must overcome host defenses to cause infection. This is especially true for corneal infections where bacteria must penetrate the epithelium in order to gain access to the stroma where bacteria can rapidly multiply, induce inflammation, and cause vision loss. Members of the Enterobacteriaceae commonly cause contact lens associated infections, but the mechanisms by which they damage corneal cells are largely unknown. Here we present evidence that Serratia marcescens and Proteus mirabilis are able to induce dramatic morphological changes in mammalian corneal cells that correlates with rapid cellular death. Secretion of ShlA-like cytolysins via type V secretion was responsible for this phenotype, and this effect was regulated by the conserved Rcs phosphorelay stress response system, including IgaA-family protein GumB. This study provides a model for stress-mediated regulation of cytolysins that induce epithelial damage and promote ocular infection.