FORMATION OF TRANSFERABLE DRUG RESISTANCE FACTOR BY RECOMBINATION BETWEEN RESISTANCE DETERMINANTS AND TRANSFER FACTORS

Nontransferable drug resistance was acquired by conjugal transmissibility when mixed cultivation was applied to many isolates of the Enterobacteriaceae. The genetic element able to confer transmissibility on nontransferable drug resistance, was henceforth termed the transfer (T) factor. Genetic studies showed that there are three mechanisms involved in the acquisition of transferability of otherwise nontransferable drug resistance; (1) transfer of the drug resistance determinant on chromosome along with the transfer of host chromosome by T factor, (2) transfer of the nontransferable R factor by complementation with T factor, (3) formation of recombinant between the T factor and the drug resistance (r) determinant. The recombinant Tr factor was transferred as a single unit by the conjugal process, and was capable of conferring drug resistance. It was transduced jointly with bacteriophage P1 as a single unit in Escherichia coli. © jointly owned by Japanese society for Bacteriology and Society of Japanese Virologists