CONJUGAL TRANSFER OF PLASMID DNA BETWEEN LACTOCOCCUS-LACTIS STRAINS AND DISTRIBUTION OF TRANSCONJUGANTS IN THE DIGESTIVE-TRACT OF GNOTOBIOTIC-RATS

The conjugational transfer of the plasmid pAM beta 1 between two strai ns of Lactococcus lactis subsp. lactis was measured in the intestinal tract of four conventional and eight gnotobiotic rats. In the conventi onal rats both donor and recipient strains were eliminated and transco njugants were not observed. Germfree rats were dosed orally with the r ecipient strain and the donor strain carrying pAM beta 1. In faecal sa mples, transconjugants were detected within the first few days after d osing, and the transconjugants established a stable population at a le vel of 10(3)-10(5) less than the recipient strain. In one group of ani mals the donor strain was eliminated from the intestine shortly after introduction, but still the transconjugants colonised the intestine. S amples from duodenum, jejunum, caecum and colon were cultured 2 or 5 w ks after dosing with the recipient strain. The concentration of transc onjugants was approximately 10-(4) c.f.u/g throughout the intestine, w hereas the concentration of recipients increased from 10(4)-10(5) c.fu ./g in jejunum to 10(8)-10(9) c.f.u./g in caecum and colon. The plasmi d pAM beta 1 seems to have conveyed to the recipient a competitive adv antage in the small intestine but not in the large intestine.