Characterizations of Leptospira-host cell interactions

Leptospirosis, caused by the pathogenic spirochete Leptospira spp, has become a re-emerging infectious disease worldwide with outbreaks occurring both in the U.S. and developing countries such as Brazil. Their ability to survive in a wide range of environmental reservoirs, including mammalian hosts, make leptospirosis the most widespread zoonosis in the world. Factors involved in the ability of this bacterium to cause disease have not been well characterized. The hallmark of leptospirosis is rapid dissemination throughout the body, where Leptospira reach the proximal renal tubules and are excreted in the urine, thereby completing their transmission cycle. This dissertation examines the ability of Leptospira to associate with eukaryotic host cells in-vitro, and discusses the probable role of surface exposed proteins in their adherence to the epithelium lining the tubules of the kidney.; Chapter 1 presents an introduction and background information on the epidemiology, and microbiology, and discusses known virulence factors involved in the pathogenesis of leptospirosis. Chapter 2 investigates the hypothesis that pathogenic Leptospira interrogans are able to penetrate polarized Madin Darby Canine Kindey (MDCK) monolayers at a rate similar to that of other invasive pathogens, without disrupting the integrity of the cell membrane. It describes how this may be a mechanisms for rapid entry into immuno-privileged sites such as the proximal tubules of the kidney. Chapter 3 describes the identification of a new family of leptospiral proteins known as Leptospira Ig-like (Lig) proteins. It reviews the initial identification of these proteins by screening lambda expression libraries with serum from human convalescent leptospirosis patients. In addition, it evaluates the presence of these proteins in both pathogenic, low passage virulent strains as well as in high passage culture attenuated strains. Prediction algorithms define the Lig proteins to the Pfam Big2 group of proteins; while high-pressure freeze substitution electron microscopy confirms their surface exposure. Chapter 4 presents the use of the AIDA-I autotransporter to display recombinant leptospiral passenger proteins on the surface of E. coli , a technique described to study the association of specific peptides with adherence to or translocation through polarized cell membranes.; This dissertation attempts to define the mechanism by which pathogenic Leptospira adhere to and disseminate through epithelial monolayers, to establish residence in the kidneys. It describes the identification of a new family of proteins that may be involved with the interaction of the bacterium and eukaryotic host cell. Inhibition of the newly identified Lig proteins may prove to be important in blocking initial colonization of the spirochete, a key factor that would interrupt the transmission of Leptospira.