Whereas negative controls remained sterile, soil seeded with M. tuberculosis reproducibly grew M. tuberculosis at every checkpoint with a yield of 26103 c.f.u. g21 at month 12 post-inoculation; the soil seeded with M. bovis reproducibly grew M. bovis at every checkpoint, with a yield of 150 c.f.u. g21 at month 12 post-inoculation. Lastly, soil seeded with M. canettii reproducibly grew M. canettii at every checkpoint with a yield of 26104 c.f.u. g21 at month 12 post-inoculation (Fig. 1). Colony morphology did not vary with time and remained characteristic of each species, with the expected morphology of mycobacteria after Ziehl– Neelsen staining. Also, Ziehl–Neelsen staining confirmed the presence of mycobacteria in the soil sample (Fig. 2a) and electron microscopy imaging showed normal mycobacteria morphology (Fig. 2b).