Intracellular growth of L. dumoffii strains within J774 mouse macrophages (A) and A549 human epithelial cells (B). The formation of colonies (CFU per milliliter) was determined at the times indicated, in triplicate, for at least two independent experiments. Error bars indicate the standard deviations determined from samples taken from one experiment. Symbols: ○, L. dumoffii wild-type strain; ▪, HOLD254; □, HOLD491; •, HMLD4001; ▵, HMLD4002.