Rapid recovery and identification of anthrax bacteria from the environment

Development of a rapid and sensitive immunoassay for detection and subsequent recovery of Bacillus anthracis spores in environmental samples

Bacillus anthracis is considered a major threat as an agent of bioterrorism. B. anthracis spores are readily dispersed as aerosols, are very persistent, and are resistant to normal disinfection treatments. Immunoassays have been developed to rapidly detect B. anthracis spores at high concentrations. However, detection of B. anthracis spores at lower concentrations is problematic due to the fact that closely related Bacillus species (e.g., B. thuringiensis) can cross-react with anti-B. anthracis antibodies, resulting in false positive detections. Subsequent polymerase chain reaction (PCR) analysis is required to differentiate virulent strains. We report here on a protocol for the rapid, sensitive detection of B. anthracis spore using the Integrating Waveguide Biosensor followed by a method for the rapid release and germination of immunocaptured spores. A detection limit of ca. 10(3) spores was achieved by incubating spores simultaneously with capture and detection antibodies ("liquid-phase" assay) prior to capture on capillary tubes/waveguides. Subsequent incubation with BHI broth directly in capillary tubes allowed for rapid germination, outgrowth, and release of spores, resulting in vegetative cells for PCR analysis.

Basis for the extraordinary genetic stability of anthrax

Over 500 isolates of anthrax bacillus from around the world represent one of the most genetically homogeneous microbes. There are three possibilities for this genetic stability: (1) anthrax has an extraordinarily high fidelity repair system, (2) genetic damage to anthrax is usually lethal, and/or (3) a highly demanding and selective process exists in its environment that is necessary for the completion of its life cycle. Using probes made from genes selected by growth of an Escherichia coli expression vector Bacillus anthracis library on hypertrophic high nitrate concentration medium, genes unique to B. anthracis were isolated. High nitration conditions generated stable chromosomal mutants that displayed altered morphology and life-cycle progression. Therefore, life-cycle progression connected to nitration, associated with host inflammatory response, selects for mutants that show life-cycle progression tightly coupled to progression of the inflammatory response to anthrax. Significant variation from this coupled progression leads to failure of anthrax to complete its life-cycle at the death of its host.