Abstract: The invention relates to a recombinant Lactobacillus strain, with limited growth and viability in the environment. More particularly, it relates to a recombinant Lactobacillus that can only survive in a medium where thymidine is present. By this strict dependency upon thymidine, thymidineless death is rapidly induced in this recombinant strain. A preferred embodiment is a Lactobacillus that may only survive in a host organism where thymidine is present, but cannot survive outside the host organism in absence of this medium compound. Moreover, the Lactobacillus strain can be transformed with prophylactic and/or therapeutic molecules and can, as such, be used to treat diseases such as, but not limited to, inflammatory bowel diseases.