FIG. 1.

Intracellular antibacterial activities of modithromycin and other antimicrobial agents against the L. pneumophila Suzuki strain in A/J mouse-derived bone marrow macrophages (A and B) and A549 human alveolar epithelial cells (C and D). These monolayer cells were infected with a 1-h incubation. After removal of the nonadherent bacteria, the infected cell layers were exposed to the antimicrobial agents for 96 h (retention experiment; A and C) or were exposed for 2 h, followed by removal of the agents and an additional 94 h of incubation in the absence of the agents (removal experiment; B and D). The macrophage and epithelial cell systems were exposed to extracellular concentrations of 4× and 16× MICs of all test agents except ampicillin, respectively. The exposure to ampicillin was at 16× MIC in both cell systems. The numbers of viable bacteria in the cells were determined at 2, 24, 48, and 96 h after infection.