FIG. 3.

Cytopathic effect of L. pneumophila SG1 against J774.1 cell monolayers. J774.1 cells (2 × 10⁴/well) were cultured in a 96-well microplate for 12 h. The cell monolayers were then infected with clinical isolates of L. pneumophila SG1 at various inoculum sizes. The microplates were cultured at 37°C for 12 h, and the contents of the plates were then decanted to remove extracellular medium and bacteria and new culture medium (200 μl) without any antibiotics was added to each well. The numbers of viable J774.1 cells after 72 h of incubation were quantified by the MTT assay and were expressed as the optical density at 550 nm. Representative results for two strains are shown. Each point represents the mean ± SD for three wells.