Conjugal Tranfer of Plasmid DNA between Lactococcus lactis Strains and Distribution of Transconjugants in the Digestive Tract of Gnotobio¬tic Rats

The conjugational transfer of the plasmid pAM β1 between two strains of Lactococcus lactis subsp. lactis was measured in the intestinal tract of four conventional and eight gnotobiotic rats. In the conventional rats both donor and recipient strains were eliminated and transconjugants were not observed. Germfree rats were dosed orally with the recipient strain and the donor strain carrying pAM β1. In faecal samples, transconjugants were detected within the first few days after dosing, and the transconjugants established a stable population at a level of 10³-10^s less than the recipient strain. In one group of animals the donor strain was eliminated from the intestine shortly after introduction, but still the transconjugants colonised the intestine. Samples from duodenum, jejunum, caecum and colon were cultured 2 or 5 wks after dosing with the recipient strain. The concentration of transconjugants was approximately 10⁴c.f.u./g throughout the intestine, whereas the concentration of recipients increased from 10⁴-10⁵ c.f.u./g in jejunum to 10⁸-10⁹ c.f.u./g in caecum and colon. The plasmid pAMβ1 seems to have conveyed to the recipient a competitive advantage in the small intestine but not in the large intestine.