Female C57BL/6 mice (6 to 8 weeks of age) were injected intravenously with 1 × 105 CFU (50% lethal dose [LD50] = 1 for wild-type 10403s L. monocytogenes) of logarithmically growing L. monocytogenes (optical density at 600 nm [OD600] = 0.5). At 48 h postinfection, spleens and livers were harvested, homogenized, and enumerated for CFU as previously described (12).