Transfer of the plasmid RP1 in vivo in germ free mice and in vitro in gut extracts and laboratory media

Abstract: The frequency of conjugal transfer of the plasmid RP1 from two different Escherichia coli donor strains (HB101 and X7, Rif^R) to the same E. coli recipient strain (X7, Nal^R) was measured in vivo (germ free mice) and in vitro (intestinal extracts, caecal contents and laboratory liquid and agar media). The transfer frequencies of the plasmid from X7, Rif^R and HB101 in vivo were not significantly different from those obtained when using intestinal extracts or caecal contents. In contrast, compared to in vivo, a significant difference in frequency of transfer was obtained from one of the donors, X7, Rif^R when using laboratory liquid media ( P < 0.05) and a significant difference in frequency was noted for donor HB101 when using laboratory agar ( P < 0.01). When comparing the ratio of transfer frequency between the two different donors, the plasmid consistently transferred at a higher frequency in vivo and in in vitro caecal contents from X7, Rif^R than from HB101 ( P < 0.05). The same pattern was observed when using in vitro intestinal extracts ( P > 0.05). In contrast, when laboratory agar was used, the opposite occurred and the transfer was greater from HB101 than from X7, Rif^R ( P < 0.05). The transfer frequency in laboratory liquid media was highly variable from donor X7, Rif^R and no significant difference ( P > 0.05) could be seen between the two donors. We conclude that the intestinal extracts and caecal contents better reflect the natural environment than any of the laboratory media tested for the parameter investigated. Furthermore, it is shown that transfer using laboratory agar did not reflect in vivo conditions. The data supports the concept of using sub-samples of an ecosystem as a microcosm for modelling the ecosystem.