Our laboratory investigates bacterial determinants that are important in the virulence, transmission, and dissemination of mucosal pathogens. We use Vibrio cholerae, the causative agent of the severe diarrheal disease cholera, as a model intestinal pathogen. V. cholerae is water-borne and maintains a reservoir in fresh and salt water in endemic areas. We are investigating the roles of V. cholerae genes at each stage of its life cycle, including both environmental and infectious stages. In addition, we study Streptococcus pneumoniae (pneumococcus) as a model respiratory tract pathogen. Pneumococcus is a commensal of the human nasopharynx, but can cause deadly invasive disease when it spreads into the lung or bloodstream. We found that pneumococcus can survive for long periods in a desiccated state on environmental surfaces, which may serve as a source of transmission.
Determining the Roles of Genes at Different Stages of the Pathogen Life Cycle
Despite many decades of study we still lack knowledge of the function and expression patterns of most genes in the V. cholerae and pneumococcus genomes. This makes understanding many aspects of their transmission, pathogenesis, and dissemination difficult, and hinders the development of vaccines, antibiotics, and diagnostics. We are developing genetic tools to increase knowledge of the roles of pathogen genes at each stage of their life cycles. One such tool for determining patterns of gene expression, is recombination-based in vivo expression technology (RIVET). This method uses a site-specific DNA recombinase as a transcriptional reporter. When expressed, the recombinase mediates the excision and loss of a selectable marker from the genome. In this way, gene induction is coupled to a heritable phenotypic change, allowing us to know if, when, and where a gene is turned on. Using RIVET we determined the complex temporal pattern of virulence and environmental gene expression that occurs when V. cholerae enters into and out of the host intestine. Through this work, we discovered that the cyclic dinucleotide c-di-GMP functions as an important second messenger in V. cholerae to mediate the inverse regulation of virulence and environmental survival genes.