The first package was found to contain Bacillus anthracis (the causative agent of anthrax), while the second was uncontaminated, but of the same soil type as found on the island.
Louis Pasteur would build on this discovery, noting that Bacillus anthracis would not grow in the presence of the related mold Penicillium notatum.
Bacillus subtilis | Bacillus | Bacillus thuringiensis | Bacillus anthracis | bacillus thuringiensis | Bacillus safensis | Bacillus pumilus |