Comparative analysis of Salmonella enterica serovar Typhi isolates from acute and chronic infections.

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Date

2018-05

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The Ohio State University

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Abstract

Salmonella enterica serovar Typhi (S. Typhi) is the causative agent of typhoid fever- a human-specific disease that results in approximately 200,000 deaths each year. With appropriate treatment, most patients recover from the acute stage of the disease. However, 3-5% of S. Typhi infections lead to a chronic infection and asymptomatic colonization in the host gallbladder – allowing carriers to unknowingly infect others despite no outward signs of illness. While it is known that S. Typhi mediates carriage through the formation of biofilms on the surface of cholesterol gallstones in the gallbladder, molecular mechanisms for chronic S. Typhi carriage are not well understood. This project compared genetic, molecular, and functional characteristics of 22 different S. Typhi isolates from confirmed acute and chronic infections, hypothesizing that the components necessary to mediate chronic carriage in the gallbladder may vary and be unique from acute clinical isolates. Biofilms of the isolates were examined utilizing a crystal violet quantification assay and confocal microscopy. The presence and relative abundance of Vi-antigen and lipopolysaccharide (LPS) were confirmed using dot blot assays with specific anti-Vi-antigen and anti-LPS antibodies and subsequent densitometric analysis. Additionally, immunofluorescent microscopy was used to evaluate Vi-antigen and LPS expression. The presence of cellulose was detected quantitatively via a microtiter-based calcofluor binding assay. Finally, the genome-sequence as well as pulsed-field gel electrophoresis (PFGE) patterns of all strains were determined. PFGE and the sequencing data informed phylogenetic relatedness determinations of the strains. Biofilm and extracellular matrix (cellulose, Vi-antigen, and LPS) expression studies revealed unexpected high variability between the S. Typhi strains. Preliminary analyses do not support the uniqueness of the chronic versus acute isolates. Additional analysis will provide a better understanding of how salmonellae enter and persist in the chronic carrier state, which may lead to targeted drug therapies to alleviate the carrier state.

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salmonella, biofilm, typhoid fever, chronic carriage

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