Aliquots of 250 mg were suspended in 250 ml PBS and were serially diluted (from 101 to 108) and immediately plated on OADC-enriched Middlebrook 7H10 agar supplemented with sodium pyruvate for M. bovis in parallel with negative controls of non-inoculated soil.
Plates were incubated at 37 uC for 4 weeks and colonies were counted. Colonies were identified as MTC organisms after Ziehl–Neelsen staining and matrixassisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF-MS) identification; colonies were collected and prepared using the previously described protocol and then applied to a MALDI-TOF-MS 96 Microflex target (Bruker Daltonic) (El Khe´chine et al.; 2011). Further, an aliquot of soil inoculated for 12 months with M. tuberculosis was filtered at 5 mm to remove large particles, and mycobacteria were observed by optical microscopy after Ziehl– Neelsen staining and by electron microscopy.