Primary in vivo infection with Lm (10 3 ), the wild type L.inn (10 7 ), or the L.inn::vgc (10 7 ) strain was performed by an intravenous injection of viable bacteria in a volume of 0.2 ml PBS. Bacterial growth in spleens and livers was determined by plating 10-fold serial dilutions of the organ homogenates on BHI agar plates. The detection limit of this procedure was 10 2 colony forming units (CFU) per organ. Colonies were counted after 24 h of incubation at 37uC.