Mitsuhashi, Susumu (Gunma University, Maebashi, Japan), Kenji Harada, Hajime Hashimoto, Mitsuo Kameda, and Mitsue Suzuki. Combination of two types of transmissible drug-resistance factors in a host bacterium. J. Bacteriol. 84:9–16. 1962.—When two types of R factor, R(TC) and R (CM.SM.SA), or R(TC) and R (CM), were brought together in a host bacterium by superinfection with both factors, loss of either one or both factors was found. In the imperfectly stable existence of both factors in a host bacterium, both factors were transmitted separately by conjugation. As the result of interaction between the two types of R factor present in a host bacterium, recombinant factors were formed, R25 (TC.CM.SM.SA) and R31 (CM.TC). The recombinant factors were able to transfer their resistance by conjugation. They were also transduced as one unit into Escherichia coli K12 by Plke phage in the same fashion as the original R11 (TC.CM.SM.SA) and R14 (CM.TC) factors independently isolated from dysenteric patients.