EPISOME-MEDIATED TRANSFER OF DRUG RESISTANCE IN ENTEROBACTERIACEAE VI. : High-Frequency Resistance Transfer System in Escherichia coli

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Watanabe, Tsutomu (Keio University, Tokyo, Japan). Episome-mediated transfer of drug resistance in Enterobacteriaceae. VI. High-frequency resistance transfer system in Escherichia coli. J. Bacteriol. 85:788–794. 1963.—R-factors (transmissible drug-resistance factors composed of the resistance-transfer factor and markers of resistance to sulfonamide, streptomycin, chloramphenicol, and tetracycline) gave rise to a high-frequency transfer system in Escherichia coli K-12 F−, F+, and Hfr strains that was similar to the high-frequency colicinogeny transfer system (HFCT) found by Stocker and Ozeki in Salmonella typhimurium with colicinogenic factor I. The procedure for obtaining a high-frequency transfer system of R-factors was identical to that for HFCT. The majority of cells of the high-frequency resistance transfer system were composed of cells which had just received R-factors by conjugation. These cells could act as highly competent donor cells for further transfer of the R-factors by conjugation. The frequencies of transfer of R-factors were as high as 1.5 to 7.5 per resistant donor cell introduced into mixed incubation with drug-sensitive recipient cells for 1 hr at 37 C, whereas the usual donor cells could transfer the R-factors at frequencies of, at most, 1:30 under similar conditions of mixed cultivation. It was also found that the aerobic conditions for growth of donor cells rather reduced the frequencies of transfer of R-factors in the usual systems. Possible mechanisms of the high-frequency resistance transfer system are discussed.

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