EFFECT OF FERMENTED MILK INTAKE ON PLASMID TRANSFER AND ON THE PERSISTENCE OF TRANSCONJUGANTS IN THE DIGESTIVE-TRACT OF GNOTOBIOTIC MICE

Plasmid transfer occurs in the digestive tract and the transconjugants may become durably established. The aim of the present work is to inv estigate the effect of probiotics on plasmid transfer and on establish ment of transconjugants in the gut. Plasmid transfers were carried out in the digestive tract of germ free mice associated with an E. coli K 12 donor strain harboring three plasmids (R388, self-transmissible, pC E325 and pUB2380, mobilisable,) and an E. coli recipient strain, PG1, of human origin (Duval-Iflah et al., 1994). Milks fermented with eithe r Lactobacillus bulgaricus or Streptococcus thermophilus or symbiosis, S85, of both strains were given daily as 1/3 of food diet. Fermented milks have no effect on the transfer of R388 and pUB2380 except a slig ht increase of TC(R388) with milk fermented with S85. Long term ingest ion of milk fermented with S85 inhibited the formation and the establi shment of transconjugants TC(pCE325). Milk fermented with L. bulgaricu s lowered the population density of TC(pCE325) in animals where they w ere already established. This phenomenon was reversible, since the den sity of TC(pCE325) increased in the same animals after cessation of su pplementation. Bacterial cultures obtained in MRS broth and given in s tate of drinking water were compared with fermented milks. Bacterial c ultures with L. bulgaricus and with S85 favoured the establishment of TC(pCE325). These results indicate for the first time that probiotics have various effects on the formation and/or establishment of transcon jugants in the gut of axenic mice. The effects depend on whether the p robiotics were cultivated in milk or in MRS, indicating that bacterial metabolites and viable bacteria can be involved.