Resistance of Escherichia coli to Penicillins I. Genetic Study of Some Ampicillin-Resistant Mutants

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Abstract
Eriksson-Grennberg, Kerstin G. (University of Uppsala, Uppsala, Sweden), Hans G. Boman, J. A. Torbjörn Jansson, and Sone Thorén . Resistance of Escherichia coli to penicillins. I. Genetic study of some ampicillin-resistant mutants. J. Bacteriol. 90: 54–62. 1965.—A number of ampicillin-resistant mutants have been isolated and characterized. Of these strains, two groups have been genetically investigated: members of one group, which are moderately resistant to ampicillin (Amp r 10 ) carry mutations in a locus which we have designated ampA ; another strain, which is resistant to high levels (50 μg/ml) of ampicillin, is a multistep mutant for which a genotype cannot yet be written. The phenotype of this strain has been designated Amp r 50 . The location of ampA was studied by the interrupted-conjugation technique, with argF, metB, mtl , and serA as reference markers. The phenotypic expression was the same for ampA and argF . These experiments, as well as recombination without selection for ampicillin resistance, indicate that ampA is located between argF and pyrB . “Broken slopes” on the recombinant curves and failure to demonstrate cotransduction make a more accurate mapping difficult. Phage P1bt transduced ampA from resistant donors to sensitive recipient strains with a frequency of 5 × 10 −7 . The ampA locus segregated in conjugation and transduction experiments with an Amp r 50 donor strain, but neither method gave a genetic transfer of high resistance to ampicillin. Penicillinase activity was demonstrated in two independent mutants carrying the ampA locus.