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August 4, 1951


JAMA. 1951;146(14):1327. doi:10.1001/jama.1951.03670140053016

During the past decade, microbial mutants have proved valuable tools for study of the mechanisms of chemotherapeutic action and of the biochemical alterations responsible for drug resistance in micro-organisms. Recent experiments by Davis illustrate the type of data that may be obtained from such studies. Nutritionally deficient mutants of Escherichia coli were isolated by an ingenious procedure1 based on the fact that, while penicillin will destroy actively growing bacteria, it has little effect on resting organisms.2 Mutants produced by exposing colonies of Esch. coli to ultraviolet irradiation were cultivated on a penicillin-containing minimal medium in which glucose, lactose, ammonia, and sulfur were the sole sources of carbon, nitrogen, and sulfur. Amino-acid-requiring mutants remained dormant and were unaffected by the penicillin but were rendered as sensitive as the nonmutants when the amino acids essential to their growth were added. Among the mutants isolated was one which grew slowly on

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