Fig. 1. An antibiotic protection assay. Two sets of Mϕ (one for the determination of phagocytic activity and the other for the determination of bactericidal activity) are incubated for a short period of time with bacteria in CM to be engulfed by Mϕ. To determine phagocytic activity, Mϕ are washed with CM containing antibiotic to kill extracellular bacteria followed by CM. They are then treated with saponin to release bacteria from Mϕ, and CFUs are determined [CFU (P)]. To determine bactericidal activity, Mϕ infected with bacteria are further incubated for a short period of time in CM containing antibiotic to kill intracellular bacteria followed by CM. They are then treated with saponin, and the number of viable bacteria in Mϕ is determined by counting the CFU after washing with CM [CFU (B)]. Bactericidal activity of Mϕ can be calculated by comparing CFU (P) with CFU (B). CM, complete medium; CFU, colony-forming units; Mϕ, macrophages.
