Both r27 and r27ΔSP increase M. tuberculosis CFU numbers in immunized mice. BALB/c mice were immunized twice with 10 μg of r27 or r27ΔSP 2 weeks apart. After 4 weeks, mice were challenged with 5 × 105 CFU of M. tuberculosis strain H37Rv; 5 weeks later, mice were sacrificed, and CFU in the spleen were determined. This experiment was repeated three times; results of one representative experiment are presented here. *, P < 0.05; **, P < 0.01 (compared to the naive group).