Spotting Deadly Spores

A new analytical technique could improve scientists’ ability to detect anthrax spores in environmental samples, such as soil or milk (Anal. Chem., DOI: 10.1021/ac2020992).

When looking for the microbe that causes anthrax, Bacillus anthracis, researchers have to worry about two analytical problems, says François Becher of the French Alternative Energies and Atomic Energy Commission: Their technique must detect tiny quantities because the minimum infectious dose for inhalation can be as little as 1,000 spores; The method must also pick out the correct Bacillus strain. Other Bacillus family members, like B. cereus, are genetically similar to anthrax and can appear to be the more dangerous bacterium.

In the method designed by Becher and his colleagues, the researchers use magnetic beads coated with anthrax-specific antibodies to pull out anthrax spores from a contaminated sample. They then treat the beads with acid to extract the bound spores. Finally, the scientists digest the spores’ proteins with proteases to produce small protein fragments for analysis by a sensitive mass spectrometry technique called multiple reaction monitoring. B. anthracis has a unique protein signature that the researchers can detect.

Becher’s team tested the method on samples of milk and soil spiked with anthrax spores. In a milliliter of milk or 10 mg of soil, the researchers could pick out as little as 7,000 spores, both of which correspond to the minimal infectious dose for ingestion.

The technique could complement current field-based measurements, such as colorimetric assays, Becher says, to verify cases of anthrax poisoning.