Mycobacteria
The live attenuated strains M. bovis BCG SSI1331 and M. bovis BCG Tokyo were used for vaccination and challenge, respectively. Mycobacteria were grown to mid-log phase in 7H9 medium containing 0.05% Tween 80 and OADC; bacteria were aliquoted and frozen at -70oC until further use. Titre of the frozen aliquots was determined by thawing an aliquot and plating serial dilutions on 7H11 agar plates.