1973 Volume 17 Issue 4 Pages 251-256
In vitro-developed resistant mutants were obtained by inoculating a clinical isolate of Aerobacter cloacae on plates containing various concentrations of ampicillin (APC). This resistance was paralleled by an increase in the formation of β-lactamase. When A. cloacae carrying the nontransmissible APC resistance-determinant (amp) was infected with a T-tet factor, a recombinant T-tet.amp factor was formed; the recombinant being conjugally transmissible and capable of conferring APC resistance on their host. This fact implies the origin of the R factor; the R factor being formed by the recombination of sex factors with nontransmissible drug resistance-determinants.
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