A pore-forming toxin enables Serratia a harmless way out from host cells

DI VENANZIO GISELA; LAZZARO MARTINA; MORALES ENRIQUE S; KRAPF DARIO Y GARCÍA VÉSCOVI ELEONORA

Illinois

Congreso; 23 rd annual MMPC - Midwest Microbial Pathogenesis Conference; 2016

University of Illinois

Several pathogens co-opt host intracellular compartments to survive and replicate, where they thereafter disperse progeny to prosper in a new niche. Serratia marcescens is an opportunistic bacterial pathogen with increasing incidence in clinical settings. However, little is known about strategies displayed by Serratia marcescens to defeat immune responses and disseminate afterwards. We have shown that Serratia invades non-phagocytic cells, surviving and multiplying within a vacuole with autophagosome-like features. Serratia manipulates cellular traffic and circumvents the progression of the Serratia-containing vacuole (SeCV) into acidic, degradative compartments, avoiding canonical elimination mechanisms. In this work, we show that ShlA pore-forming toxin (PFT) commands Serratia escape from invaded cells. A PFT-dependent Ca2+ increase was observed in SeCVs tight proximity, while intracellular Ca2+ sequestration prevented Serratia exit. Accordingly, a Ca2+ surge rescued a ShlA-deficient strain exit capacity, demonstrating that Ca2+ mobilization is essential for egress. ShlA expression injures the SeCV membrane without compromising the invaded cell viability. As opposed to wild-type-SeCV, the mutant strain-vacuole was wrapped by actin filaments, showing that ShlA expression rearranges host actin. Moreover, alteration of actin polymerization hindered wild-type Serratia escape, while increased intracellular Ca2+ reorganized the mutant strain-SeCV actin distribution, restoring wild-type-SeCV phenotype. Our results demonstrate that, by ShlA expression, Serratia triggers a Ca2+ signal that reshapes cytoskeleton dynamics and ends up pushing the SeCV load out of the cell, in an exocytic-like process. These results disclose that PFTs can be engaged in allowing bacteria to exit without compromising host cell integrity.