R-plasmic transfer from Serratia liquefaciens to Escherichia coli in vitro and in vivo in the digestive tract of gnotobiotic mice associated with human fecal flora

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Abstract
A strain of S. liquefaciens harbors a conjugative R-plasmid responsible for resistance to the following 14 antibiotics: ampicillin, carbenicillin, cephalothin, butirosin, neomycin, paramomycin, kanamycin, lividomycin, gentamicin, tobramycin, streptomycin, tetracycline, sulfonamide and chloramphenicol, which belong to 5 families, the .beta.-lactamines, the aminoglycosides, the tetracyclines, the sulfonamides and the phenicols. Resistance to the 14 antibiotics was co-transferred by in vitro conjugation between S. liquefaciens and strains of E. coli. Mating between S. liquefaciens and E. coli occurred in vivo in the digestive tract of axenic mice and gnotobiotic mice associated with the whole human fecal flora. Mating between these 2 strains occurred even when the donor S. liquefaciens strain was transient in the digestive tract of the gnotobiotic host animals. A dense population of Bacteroides (1010 viable cells/g of fresh feces) did not hinder this mating. All the matings occurred in the absence of an antibiotic selection pressure and the resulting transferred strain of E. coli did not have the same colonizing capacity as the recipient parental strain. During antibiotic administration to mice and after the end of the drug intake, the transconjugant became established in the dominant population and replaced the parental recipient strain.