Studies on Resistance Transfer Factors. II. Transmissible Resistance to Eight Antibacterial Drugs in a Strain of Escherichia coli

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Abstract
The transmissible resistance to 8 drugs in the naturally occurring E. coli strain 81 was studied. In the donor strain, the rate of spontaneous loss of the resistance markers carried by factor-R-81 is very low. In the donor population and the Salmonella and Shigella recipient populations infected with factor-R-81, resistance to chloramphenicol, streptomycin and sulfa drugs is at more than 1 level for each drug; whereas of the 2 resistance levels to the penicillins found in the donor, only the lower was conferred. Resistance to all 8 drugs was conferred within as little as 2 min. of incubation of mixed cultures, and a maximum accumulation of all markers transferred was found at 20 min. factor-R-81. The segregates in the new hosts at rates varying for each particular recipient strain. ''Curing'' of the donor by acriflavin was accomplished by a segregation process, and the factor was reconstituted in an infective form in the initial cured host. The pecularities of the transmissible resistance of this clinical strain are discussed.