The Production of Mutations in Staphylococcus Aureus by Irradiation of the Substrate

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Abstract
Expts. were conducted in which bacteria were allowed to reproduce in a medium containing known substances which had been subjected to u.-v. irradiation. Mutations to forms resistant to penicillin were induced in S. aureus by irradiation of the nutrient broth. In synthetic media, resistance to penicillin and streptomycin was induced by irradiation of the amino acids and vitamins, or of the amino acids alone. That resistance to penicillin and streptomycin was the result of different mutations was substantiated by transferring the organisms. Penicillin-resistant organisms behaved very differently from the controls when streaked on plates containing penicillin but very similarly to the controls when tested on streptomycin agar. The converse was true for the streptomycin-resistant strains. Furthermore, preliminary expts. are said to indicate that it is possible, by suitable irradiation procedures, to increase the rate of mutation to penicillin resistance without affecting the rate of mutation to streptomycin resistance. Aging of the irradiated material, especially when accompanied by heat treatment, reduces the capacity to induce mutations. This suggests a mechanism involving a shift to a higher energy level and subsequent energy transfer. The production of different chemical compounds under the influence of irradiation is mentioned as a possible alternative explanation ,.

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