Beschreibung:
<jats:p>The <jats:italic>Proteus mirabilis</jats:italic> strains PG193 (<jats:italic>his</jats:italic><jats:sup>‐</jats:sup> <jats:italic>tet</jats:italic><jats:sup>+</jats:sup> <jats:italic>rec</jats:italic><jats:sup>+</jats:sup>), PG273 (<jats:italic>thr</jats:italic><jats:sup>‐</jats:sup> <jats:italic>tet</jats:italic><jats:sup>+</jats:sup> <jats:italic>rec</jats:italic><jats:sup>+</jats:sup>), and PG672 (<jats:italic>thr</jats:italic><jats:sup>‐</jats:sup> <jats:italic>tet</jats:italic><jats:sup>+</jats:sup> <jats:italic>rec</jats:italic><jats:sup>+</jats:sup>) are full resistant to 40 μg tetracyclin/ml, similar to other 513 wild type strains tested. The F‐plasmid was introduced from <jats:italic>Escherichia coli</jats:italic> WF<jats:sup>+</jats:sup> into these strains and into the <jats:italic>tet</jats:italic><jats:sup>‐</jats:sup> <jats:italic>P. mirabilis</jats:italic> Pm2098 by conjugation. Pure F<jats:sup>+</jats:sup> <jats:italic>P. mirabilis</jats:italic> strains are sensitive to the F‐specific phage <jats:italic>fr</jats:italic>. The transfer of the F‐plasmid from F<jats:sup>+</jats:sup> <jats:italic>P. mirabilis</jats:italic> back to <jats:italic>E. coli</jats:italic> K12 strains occurs with high frequency.</jats:p><jats:p>In several cases the F‐plasmid is able to transfer the tet‐gene from <jats:italic>tet</jats:italic><jats:sup>+</jats:sup> <jats:italic>rec</jats:italic><jats:sup>+</jats:sup> <jats:italic>P. mirabilis</jats:italic> strains (PG193, PG273) to <jats:italic>E. coli</jats:italic> recipients but not from F<jats:sup>+</jats:sup> <jats:italic>P. mirabilis tet</jats:italic><jats:sup>+</jats:sup> <jats:italic>rec</jats:italic><jats:sup>‐</jats:sup> (PG672) or from F<jats:sup>+</jats:sup> <jats:italic>P. mirabilis tet</jats:italic><jats:sup>‐</jats:sup> strains (Pm2098).</jats:p><jats:p><jats:italic>E. coli tet</jats:italic><jats:sup>+</jats:sup> recombinants are sensitive to the F‐specific phage <jats:italic>fr</jats:italic>. They harbor F‐plasmids stably linked to the tet‐gene. Such recombinant plasmids are transferable with high frequency to other F<jats:sup>‐</jats:sup>R<jats:sup>‐</jats:sup> members of the <jats:italic>Enterobacteriaceae</jats:italic> but with reduced frequency of transmission to <jats:italic>E. coli</jats:italic> Hfr(H) indicating a superinfection immunity.</jats:p><jats:p>These results coincide with the Campbell modell and point to the fact that the “gene pick up” may be the (or one) way of R‐plasmid origin as proposed by Watanabe (1963).</jats:p>