Inflammasome Activation by Bacterial Outer Membrane Vesicles Requires Guanylate Binding Proteins.

Enterotoxigenic E. coli (ETEC) causes traveler's diarrhea and infant mortality in underdeveloped countries, and Pseudomonas aeruginosa is an opportunistic pathogen for immunocompromised patients. Like all gram negative bacteria studied to date, ETEC and P. aeruginosa produce small outer membrane vesicles that can serve as delivery "bombs" to host tissues. Vesicles contain a subset of outer membrane and soluble periplasmic proteins and lipids. In tissues and sera of infected hosts, vesicles have been observed to bud from the pathogen and come in close contact with epithelial cells. Despite their association with disease, the ability of pathogenic bacteria to distribute an arsenal of virulence factors to the host cells via vesicles remains relatively unexplored.

In our lab, we focus on the genetic, biochemical and functional features of bacterial vesicle production. Using a genetic screen, we have identified genes essential in the vesiculation process, we have identified specific proteins that are enriched in vesicles, and we have identified critical molecules that govern the internalization of vesicles into host cells. Using biochemical analysis of purified vesicles from cell-free culture supernatants, we have found that heat-labile enterotoxin, an important virulence factor of ETEC, is exported from the cells bound to the external surface of vesicles. Presented in this context, it is able to mediate the entry of the entire ETEC vesicle into human colorectal tissue culture cells. We have also discovered that the ability of vesicles to bind to specific cell types depends on their strain of origin: for example, P. aeruginosa vesicles produced by a strain that was cultured from the lungs of a patient with Cystic Fibrosis adhered better to lung than to gut epithelial cells, whereas a strain that was isolated from sera showed no such preference for lung cells. The vesicles stimulate epithelial cells and macrophages to elicit a cytokine response that is distinct from that of LPS (a major component of the vesicles) alone.

These studies will provide new insights into the membrane dynamics of gram-negative bacteria and consequently aid in the identification of new therapeutic targets for important human pathogens.

Bacterial infections remain one of the leading causes of morbidity and mortality worldwide. The Coers lab seeks to understand fundamental aspects of the innate immune response to bacterial pathogens as well as the corresponding immune evasion strategies evolved by human pathogens undermining immunity in order to establish infections. Defining innate immunity and microbial counter-immunity pathways on a molecular level will provide roadmaps for the rational design of novel antimicrobial therapies and improved vaccine strategies against pathogens such as the enteric pathogen Shigella or the sexually transmitted pathogen Chlamydia.

In addition to making major inroads in the fields of innate immunity, inflammation and bacterial pathogenesis, our second, but equally important goal, is to train the next generation of scientists in an environment that prioritizes excellence, research integrity, teamwork and inclusiveness. We strive to create an environment of mutual respect, openness, collegiality, integrity and, last but not least, fun, which promotes and awards curiosity and fosters collaborations. We strongly believe that diversity promotes excellence.