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Eriksson-Grennberg, Kerstin G. (University of Uppsala, Uppsala, Sweden),Hans G. Boman, J. A. Torbjörn Jansson, and Sone Thorén . Resistance ofEscherichia 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 (Ampr 10 ) carry mutations in a locus which we have designatedampA ; 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 Ampr 50 . The location ofampA was studied by the interrupted-conjugation technique, withargF, metB, mtl , andserA as reference markers. The phenotypic expression was the same forampA andargF . These experiments, as well as recombination without selection for ampicillin resistance, indicate thatampA is located betweenargF andpyrB . “Broken slopes” on the recombinant curves and failure to demonstrate cotransduction make a more accurate mapping difficult. Phage P1bt transducedampA from resistant donors to sensitive recipient strains with a frequency of 5 × 10−7 . TheampA locus segregated in conjugation and transduction experiments with an Ampr 50 donor strain, but neither method gave a genetic transfer of high resistance to ampicillin. Penicillinase activity was demonstrated in two independent mutants carrying theampA locus.

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