Intracellular growth. MM6 macrophages (A) and J774.A1 macrophages (B) were infected with M. bovis BCG(pAS-MDP1) and M. bovis BCG (pMV261). The DNA of intracellular bacteria was quantified by real-time PCR in 10 μl of a DNA preparation of lysed macrophages. The amounts of intracellular bacteria post infection are represented by the values at 6 h in part (A) and by the values at 4 h in part (B). The values represent the mean of three independent infections with the standard deviation. The single asterisks indicate values that varied significantly (P < 0.05) according to the student's t test.