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

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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 (Ampr10) 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 Ampr50. 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 Ampr50 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.

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