| Bacillus anthracis, the etiological agent of anthrax, has received much attention because of the 2001 bioterrorism attacks. However, anthrax has been a serious concern for thousands of years and remains a threat to human populations that come in contact with the organism. In order to develop novel treatments and therapeutic strategies, a thorough understanding of B. anthracis virulence mechanisms and how they are regulated is essential. The present studies began by assessing the effect of glycerol monolaurate (GML), a potential therapeutic, on B. anthracis. Previous studies with GML have shown that it affects the expression of virulence factors of Staphylococcus aureus, Enterococcus faecalis. The GML studies showed that the compound is bacteriostatic to B. anthracis at a concentration of 15 mug/ml. At a concentration of 10 mug/ml, GML specifically inhibits the transcription of the three toxin genes. Since GML acts through two-component systems, the results of these experiments suggest that a two-component system may be responsible for regulating expression of virulence factors. This result led to the next phase of studies where we identified a two-component regulatory system, with homology to the ResD-ResE system in B. subtilis, that we named bacillus respiratory response A and B (BrrA-BrrB). When a brrA mutant was constructed, the mutant B. anthracis strain was deficient in some aerobic and anaerobic characteristics as well as toxin production. Purified BrrA was shown to bind the promoter region of pagA, the gene for one of the three toxin components, suggesting that BrrA directly regulates the gene expression of toxin components. Finally, in order to determine if BrrA-BrrB is important for virulence in an in vivo model, we developed a cutaneous model of anthrax infection. Upon subcutaneous injection with the parent Sterne strain of B. anthracis, Dutch belted rabbits formed abscesses with many neutrophils and some macrophages recruited to the injection site, much like the pathogenesis of human infection. However, animals injected with the brrA mutant strain formed smaller abscesses that cleared in a few days, suggesting that the virulence factors regulated by BrrA-BrrB are important for the massive influx of immune cells during parent strain infection. |
