Faculty and Research
Meta J. Kuehn, PhD
Department of Biochemistry
Like all gram negative bacteria studied to date, Enterotoxigenic E. coli (ETEC) and Pseudomonas aeruginosa produce small outer membrane vesicles that can serve as delivery "bombs" to host tissues. ETEC causes traveler's diarrhea and infant mortality in underdeveloped countries, and P. aeruginosa is an opportunistic pathogen for immunocompromised patients, particularly those with cystic fibrosis (CF). Despite their association with disease, the ability of pathogenic bacteria to distribute an arsenal of virulence factors to host cells via vesicles remains relatively unexplored.
The research in my laboratory currently focuses on the genetic, biochemical and functional features of bacterial vesicle production. We have have isolated mutants in E. coli genes critical in the vesiculation process and are in the process of characterizing these Dissection of the toxin secretory pathway revealed that the General Secretory Pathway is responsible for the secretion of an important virulence determinant of ETEC, heat labile enterotoxin, to the cell surface. Consequently, when vesicles bud from ETEC cells, they display toxin on their outer surface. Using purified fluroescently labeled vesicles, we have identified critical molecules that govern the interaction between toxic bacterial vesicles and human epithelial cells. It is the toxin bound to the exterior of the vesicle membrane that enables vesicle entry into and intoxication of human cells. Thus we found that toxin-host cell receptor binding is the molecular basis for the toxicity of ETEC-derived vesicles.
Using proteomics, we have identified vesicle components specific for P. aeruginosa strains isolated from the lungs of CF patients. 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 CF adhered better to lung than to gut epithelial cells, and a strain that was isolated from sera showed no preference for lung cells.
These long term goal of these studies is to understand both the basic membrane processes that lead to vesicle formation and the role of vesicles in disease. As a consequence, we may identify new therapeutic targets for virulent human pathogens.