A proteína pic produzida por Escherichia coli induz sepse letal em modelo murino

Abstract

Some Escherichia coli strains are pathogens responsible for a variety of diseases, and albeit using distinct mechanisms of pathogenesis, have in common the production of Pic, or protein involved in colonization. We have recently shown that Pic mediates immune evasion by the direct cleavage of complement molecules, significantly reducing complement activation by all three pathways. The aim of this study was to investigate the action of Pic in a murine model of sepsis. Six to eight-week-old female Swiss mice were intraperitoneally inoculated with Pic-producing E. coli (F5), F5Δpic mutant or apyrogenic water (control). Animal survival was monitored for 5 days (n= 6 animals/group) and a subset of mice (n= 6 animals/group) was euthanized after 12 h for sample acquire from blood, peritoneal lavage and organs. The parameters evaluated were cellularity from blood, peritoneal cavity and organs; inflammatory mediators production; quantity of colony forming units (CFU's); immunophenotyping of cells from spleen and peritoneum; and histopathology of organs. Intraperitoneal inoculation of Pic-producing bacteria induced 100% death within 24 h, different from the other groups where no death was observed. The CFU count of bacteria in the organs was significantly higher in F5 than other groups. Besides, only F5 was viable on bloodstream. Hematological analysis showed a decrease of total leukocytes, mainly lymphocytes. NO and cytokines (IFN-γ, TNF-α, IL-6, IL-12, IL-10 and MCP-1) were detected in serum, as well as on peritoneal lavage (excepting IL-12) of F5 group in significantly higher levels than other groups. Immunophenotyping of spleen and peritoneum cells revealed that there was a low expression of co-receptors on lymphocytes and macrophages in F5 group, indicating that the activation and function of these were compromised. Therefore, these results evidenced that Pic represents an important virulence factor, allowing the survival of the bacterium on bloodstream and several organs, as well as inducing a high production of pro-inflammatory mediators by the host, leading to a sepsis and death.