Recent literature review of soil processing methods for recovery of Bacillus anthracis spores

Identifying virulent Bacillus anthracis within soil is a difficult task due to the number and diversity of other organisms and impeding chemical constituents within soil. Regardless of the detection assay, the initial sample must be processed efficiently to ensure that debris, chemical components, and biological impurities do not obstruct downstream analysis. Soil sample processing protocols can be divided into two general types: indirect and direct. There are two requirements for successful indirect isolation of B. anthracis from soil samples: dissociate the spores from the soil particles and physically separate the free spores from the soil particles. Adding an aqueous carrier medium to a soil sample creates a sample slurry for easier manipulation. Centrifugation, high specific gravity separation, immunomagnetic separation, filtration, and settling have been used to physically separate spores from soil. Direct processing utilizes a soil sample without first separating the spores from the bulk sample and falls under two principal types: culturing on B. anthracis selective agar and bulk DNA extraction. Direct and indirect processing steps each have associated advantages and disadvantages. The objective of this review was to consolidate information acquired from previous research, focusing primarily on data gleaned in the last decade, on the processing of soils contaminated with B. anthracis. As shown in this review, an optimized soil-processing protocol with a known recovery rate and associated confidence intervals is needed. A reliable processing protocol would allow for multiple investigators and laboratories to produce high-quality, uniform results in the event of a B. anthracis release.