Anthrax Early Events: Molecular pathogenesis, genomics and proteomics
Our group investigates models for the first hours of anthrax infections, in vivo germination of the Bacillus anthracis endospore, macrophage survival, growth and escape of the vegetative bacilli into the blood. Outside the host, endospores remain metabolically-dormant, preserving virulence even when exposed to harsh environmental conditions. Endospores are the anthrax contagion, entering the body where they are phagocytosed by regional macrophages. Endospores "sense" the new locale, germinate and outgrow to a vegetative state. After escape, massive bacteremia, toxemia and death ensue. We are examining each of these stages and defining discrete mutants blocked at each step. Our data indicate that anthrax endospores have unique in vivo sensory and signalling mechanisms for triggering germination. Germination occurs rapidly in cultured macrophages. Non-pathogenic Bacillus sp. endospores show no increased germination in macrophages. B. anthracis transposon-mediated mutagenesis systems and directed knock-outs allow selection of individual endospore mutants incapable of germination in macrophages but fully capable of germination and outgrowth in bacterial media, the identification of genes involved in the intracellular events of bacterial growth, including new toxin genes. We employ, as experimental tools, methods of molecular pathogenesis, functional genomics and functional proteomics. Our specific goals are to:
- define and characterize the germination genes of B. anthracis and host chemical signals to determine their roles in the host-specific germination response;
- determine defined intracellular events and bacterial genes used by the vegetative bacilli allowing for survival and escape from the macrophage, and;
- understand the relevance of B. anthracis host-specific germination systems and early intracellular events in terms of anthrax pathogenesis.
Knowledge of these critical "establishment" stages of anthrax may provide targets for early intervention after exposure to anthrax endospores. Understanding this rapid and dramatic switch, from absolute metabolic dormancy of the endospore to growing virulent bacilli allows anthrax to be exploited as an effectual model for examining the earliest stages of a bacterial infectious cycle.
Ireland , J. & P. Hanna. 2002. Macrophage-enhanced germination of Bacillus anthracis endospores requires gerS.Ê Infect. Immun. 70:5870-5872.
Ireland , J. and P. Hanna. 2002. Amino acid- and purine ribonucleoside-induced germination of Bacillus anthracis delta-Sterne endospores: gerS mediates responses to aromatic ring structures. J. Bacteriol. 184:1296-1303.
Pannifer, A., T. Wong, R. Schwarzenbacher, M. Renatus, C. Petosa, J. Bienkowska, D. Lacy, R. Collier, S. Park, S. Leppla, P. Hanna and R. Liddington. 2001. Crystal structure of the anthrax lethal factor. Nature 414:229-233.
T. Dixon, A. Fadl, T. Koehler, J. Swanson and P. Hanna. 2000. Early Bacillus anthracis-macrophage interactions: intracellular survival and escape. Cel. Microbiol. 2:453-63.
T. Dixon, B. Meselson, J. Guillemin and P. Hanna. 1999. Medical Progress in Anthrax.
N. Eng. J. Med. 341:815-26.
S. Hammond, and P. Hanna. 1998. Lethal factor active-site mutations affect catalytic activity in vitro. Infect. Immun. 66:2374-8.