S. marcescens is an etiological agent of urinary tract and respiratory infections, endocarditis, osteomyelitis, eye and wound infections, meningitis and sepsis. Serratia shows a high incidence in immunocompromised patients and also in neonatal intensive care units. The analysis of pathogenic mechanisms of opportunistic bacteria such as Serratia, with high impact in under-developed and developing countries, has given priority to the understanding of antibiotic multiple resistances. This information is valuable to adopt strategies to fight infectionsin the short term. However, for most opportunistic bacteria, the analysis of virulence mechanisms and factors involved in the long term pathogen-host interaction (colonization, invasion and dissemination) has been relegated. This knowledge constitutes the basis for the development of alternative therapeutic targets.

Our laboratory has demonstrated that Serratia marcescens has the capacity not only to promote its internalization in non-phagocytic cells but also to survive and proliferate intracellularly. We showed that the Serratia-containing vacuole deploys a traffic pathway that diverges from the canonical route, avoiding the physiological mechanisms that promote bacterial elimination. After intracellular proliferation, the expression of a bacterial effector allows Serratia to egress from the invaded cell by a non-lytic process, granting its dissemination. In parallel, we have demonstrated that phenotypes such as swimming and swarming motility, adherence to host cells, the expression levels of the cytolysinsShlA and PhlA, and the ability to produce outer membrane vesicles depend on the activation status of the Rcs signal transduction system. These results revealed that the Rcs system is key for the proper temporal and spatial regulation of the Serratia pathogenic traits expression.

In sum, our group has elucidated a repertoire of adaptive regulatory mechanisms and specific effectors deployed by Serratia to survive, proliferate and disseminate outside and inside the host. Because all of these features, Serratia marcescens constitutes an optimal model to further contribute to the understanding of bacteria-host interaction.