In-vivo transfer of resistance plasmids in rat, human or pig-derived intestinal flora using a rat model.

Germ-free rats associated with either rat- (RIF), human- (HIF) or pig-(PIF) derived Enterobacteriaceae-free intestinal flora were used for in vivo experiments to detect transfer of antibiotic resistance. Transfer of resistance was observed most frequently from the porcine donor strain to acceptor strain Escherichia coli K12, showing the highest number of transconjugants in the faeces of HIF-rats. The rats associated with the human donor strain and E. coli K12 as acceptor showed transconjugants less frequently. Only the HIF-rats yielded transconjugants on each sampling day and none at all could be isolated from the PIF-rats. Almost no transconjugants were found in the faeces of rats associated with the pig donor strain and a wild human E. coli strain as acceptor. Factors such as the nature of the donor and recipient strains as well as the origin of the intestinal flora seemed to have an influence on plasmid transfer. Transferability was highest in the HIF-rats and could be increased by administration of lincomycin. This study showed that in vivo transfer of resistance plasmids is possible in rats associated with intestinal floras of different origins. The human intestinal flora seemed to permit better transfer of resistance than that derived from the pig or the rat.