Growth in broth culture. Broth cultures from M. bovis BCG(pAS-MDP1) and M. bovis BCG(pMV261) were diluted into Middlebrook 7H9 broth to give an initial OD (600 nm) of 0.02 to 0.04 and the cultures were incubated during 59 days. The growth curves of the strains were generated by determination of the ATP content [displayed as relative light units (RLU)] in the cultures with a luciferase assay. The values represent the mean of three independent cultures with the standard deviation. The single asterisks indicate values that varied significantly (P < 0.05) and the double asterisks indicate values that varied very significantly (P < 0.01) according to the student's t test.