[In vivo plasmid transfer between strains of Escherichia coli in the chicken digestive system]

To study the transfer of plasmids in the gut of chickens, we introduced a conjugative plasmid pGB99, which encodes resistance to chloramphenicol (Cm), tetracycline (Tc), sulphonamide (Su) and trimethoprim (Tm), into a nalidixic acid mutant of an antibiotic sensitive avian E. coli strain (BN118). The transfer of the plasmid between the nalidixic acid resistant strain and a streptomycin resistant mutant of the same strain was studied in the gut of dixenic and gnotobiotic chickens carrying an avian microbial flora devoid of resistant E. coli. Half of the chickens received tetracycline in the drinking water. The results indicate that the plasmid transfer occurred rapidly after inoculation in the gut of the dixenic chickens, with a persistent level of 10(4) transconjugants/g in the feces of chickens without tetracycline. During the administration of tetracycline, selection of the strains harboring the R plasmid (donor strains and transconjugants) was observed. In the gut of the chickens carrying the avian flora plasmid transfer between the donor and recipient strain BN118 was only observed in the group of animals receiving tetracycline. However transfer has probably occurred between the donor strain and the commensal E. coli of the flora in animals of the two groups.