Salmonella biofilm formation, virulence, transmission and vaccine development

Project Team: Aaron White, Lindsay Balezantis, Michelle Gerber, Ryan Krochak, Madeline McCarthy, Sivaranjani Murugesan, Akosiererem Sokaribo

Pathogenic Salmonella strains are a prominent cause of human food-borne infections. Despite decades of research it is not well understood how these pathogens survive outside the human body. The Salmonella strains that cause gastroenteritis, a localized infection of the GI tract, are thought to cycle back and forth between their hosts (humans and animals) and the environment. In contrast, the strains that cause systemic infections, such as typhoid fever, are human-adapted and may have a reduced environmental phase. This has implications for understanding the mechanisms of transmission and for the development of strategies to reduce the spread.

Our research is focused on understanding the lifecycle of pathogenic Salmonella strains, specifically in biofilms. Biofilms are dense collections of cells that stick together due to the production of extracellular carbohydrate and protein polymers. Biofilms provide a distinct survival advantage under stressful conditions and are thought to represent the predominant form of bacterial life in nature.

We discovered gastroenteritis-causing Salmonella strains undergo phenotype switching during biofilm formation, resulting in specialized groups of cells – single cells that are virulent and biofilm cells that can survive long periods of time. The presence of both of these cell types allows for smooth transitions between the host and the environment. This concept has implications for many aspects of Salmonella research including: characterizing survival and transmission differences for each cell type, investigating if the immune system responds differently to each cell type, comparing strains causing gastroenteritis and strains causing systemic infections, and learning how to design better vaccines to prevent human and animal infections.