James M. Fleckenstein, MD

Diarrheal illnesses remain a leading cause of death among young children in developing countries. Research in our laboratory focuses on the molecular pathogenesis of enterotoxigenic Escherichia coli (ETEC). These organisms are one of the leading causes of diarrhea-associated mortality in young children in the developing world, and are perennially the most common etiology of diarrhea in travelers. Interestingly, ETEC have re-emerged in the form of large-scale foodborne outbreaks in industrialized countries including the U.S. These organisms constitute a diverse E. coli “pathotype” that share in their ability to effectively deliver heat-labile (LT) and/or heat-stable (ST) toxins to respectively activate production of cAMP and cGMP in host intestinal epithelial cells. Both of these cyclic nucleotides activate protein kinases to phosphorylate and activate the cystic fibrosis transmembrane conductance regulator (CFTR), ultimately leading to a net loss of salt and water in the small intestine to cause the watery cholera-like diarrhea characteristic of these pathogens. Although ETEC have been a target of vaccine development efforts for several decades, progress has been hampered by heterogeneity in key targets (namely plasmid-encoded fimbrial antigens known as colonization factors or CFs), incomplete protection afforded by anti-LT immunity, and the poor immunogenicity of ST molecules, (typically small peptides of ~18-19 amino acids).

Our lab focuses on the identification and molecular characterization of novel ETEC virulence factors that could serve as targets for vaccine development. Studies in the lab use a variety of molecular techniques and in vitro and in vivo models to elucidate the role of these novel virulence factors in several key steps essential in the pathogenesis of these organisms: bacterial adhesion, intestinal colonization, and finally toxin delivery. Current projects involving genome, transcriptome, and immuno-proteome analysis of these pathogens seek to accelerate identification of potential vaccine targets. The principal long-term goal of these studies is to provide additional molecular details to aid rational selection of target antigens and inform future vaccine development efforts for these important pathogens.

Bibliography – James M. Fleckenstein