Episome-Mediated Transfer of Drug Resistance in Enterobacteriaceae IX. Recombination of an R Factor with F

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Watanabe, Tsutomu (Keio University, Tokyo, Japan), and Chizuko Ogata. Episome-mediated transfer of drug resistance in Enterobacteriaceae. IX. Recombination of an R factor with F. J. Bacteriol. 91:43–50. 1966.—R factors can be transduced in Salmonella typhimurium with phage P-22, and a majority of the drug-resistant transductants are unable to transfer their drug resistance by cell-to-cell contact, as we have previously reported. Several exceptional types of transductants of S. typhimurium, with the markers of resistance to sulfonamide, streptomycin, and chloramphenicol, were recently obtained by transduction with phage P-22 of a four-drug-resistance R factor carrying the markers of resistance to sulfonamide, streptomycin, chloramphenicol, and tetracycline. They were exceptional in that they had low conjugal transferability of their drug resistance. When one of these exceptional transductants (38R) was transferred to an F+ strain of Escherichia coli K-12, 38R acquired high transferability in its further transfer. This high transferability was found to be due to the recombination of 38R with F. Transductant 38R was of the fi+ (fi = fertility inhibition) type, and did not show superinfection immunity against fi+ and fi− R factors. The recombinant 38R·F was genetically very stable and resistant to elimination with acridines. It did not show superinfection immunity against fi+ and fi− R factors, but did show superinfection immunity against F. Further, 38R·F did not restrict a female-specific phage (W-31), unlike wild-type F. F− and R− segregants were isolated from this recombinant 38R·F, and these segregants exhibited genetic characteristics different from the original R, its transductant 38R, and wild-type F.

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