In vivo survival and growth kinetics of bacteria were followed by determining the number of bacteria in spleens and livers of infected mice. As expected, regardless of the dose of infection, the wild type L.inn strain was progressively cleared from both organs ( Fig. 1A) whereas the L.inn::vgc strain successfully survived in both spleen and liver during the first two days after infection as indicated by the bacterial numbers that increased in both spleen and liver till day 2 and gradually decreased over days 3 and 4 postinfection. On the other hand, the bacterial numbers of the wild type Lm, increased from day 1 till day 4 post-infection in both spleen and liver.