Ecotin protectsSalmonellaTyphimurium against the microbicidal activity of host proteases

Abstract

ABSTRACTSalmonella entericaserovar Typhimurium causes acute diarrhea upon oral infection in humans. The harsh and proteolytic environment found in the gastrointestinal tract is the first obstacle that these bacteria face after infection. However, the mechanisms that allowSalmonellato survive the hostile conditions of the gut are poorly understood. Theecotingene is found in an extensive range of known phyla of bacteria and it encodes a protein that has been shown to inhibit serine proteases. Thus, in the present work we studied the role ofecotinofSalmonellaTyphimurium in host-pathogen interactions. We found thatSalmonellaTyphimurium Δecotinstrain exhibited lower inflammation in a murine model ofSalmonellainduced colitis. The Δecotinmutant was more susceptible to the action of pancreatin and purified pancreatic elastase. In addition, the lack ofecotinled to impaired adhesion to Caco-2 and HT-29 cell lines, related to the proteolytic activity of brush border enzymes. Besides, Δecotinshowed higher susceptibility to lysosomal proteolytic content and intracellular replication defects in macrophages. In addition, we found Ecotin to have a crucial role inSalmonellaagainst the microbicide action of granules released and neutrophil extracellular traps from human polymorphonuclear leukocytes. Thus, the work presented here highlights the importance ofecotininSalmonellaas countermeasures against the host proteolytic defense system.IMPORTANCEThe gastrointestinal tract is a very complex and harsh environment.Salmonellais a successful food borne pathogen, but little is known about its capacity to survive against the proteolysis of the gut lumen and intracellular proteases. Here, we show that Ecotin, a serine protease inhibitor, plays an important role in protectingSalmonellaagainst proteases present at different sites encountered during oral infection. Our results indicate that Ecotin is an important virulence factor inSalmonella, adding another tool to the wide range of features this pathogen uses during oral infection.