The experiment aimed to specifically monitor the passage of lactobacilli in vivo after oral administration. The green fluorescent protein (GFP) gene was cloned downstream from the constitutive p32 promoter from L. lactis subsp. cremoris Wg2. The recombinant expression vector, pLEM415-gfp-p32, was electroporated into Lactobacillus plantarum (L. plantarum) isolated from goat. Green fluorescent protein (GFP) was successfully expressed in L. plantarum. After 2 h post-administration, transformed Lactobacillus could be detectable in all luminal contents. In the rumen, bacteria concentration initially decreased, reached the minimum at 42 h post-oral administration and then increased. However, this concentration decreased constantly in the duodenum. This result indicated that L. plantarum could colonize in the rumen but not in the duodenum.

The transformed L. lactis, L. brevis, L. johnsonii, L. murinus, and the endogenous murine lactobacillus strain failed to persist in the mouth. Transformed L. plantarum, however, persisted in the mouth and comprised up to 25% of the total lactobacilli at 18 h and 10% at 24 h after feeding. L. plantarum recovered after feeding retained its ability to secrete beta-lactamase into culture medium efficiently. Beta-lactamase activity could be detected in oral secretions at 8 h after feedings. After repeated feedings, however, the L. plantarum containing pKTH2121 gradually lost its ability to persist after feedings. This experiment demonstrates that L. plantarum can transiently colonize the oral mucosa in large numbers, while continuously secreting foreign proteins, raising the possibility of using lactobacilli as a vector for delivery of oral mucosal peptides.