THE EFFECT OF ULTRAVIOLET IRRADIATION ON THE DEVELOPMENT OF RESISTANCE OF BACTERIA TO ANTIBIOTICS

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Abstract
U.-v. irradiation of Micrococcus pyogenes var. aureus did not induce increased resistance to penicillin or streptomycin. Irradiation of culture media prior to inoculation did not induce increased resistance to penicillin. Irradiation of Escherichia coli (K-12) caused no increase in the proportion of cells resistant to low levels of streptomycin (1-2 [mu]g./ml.), and either no increase or a slight and evanescent increase in the proportion resistant to high concns. (20-40 [mu]g./ml.), but did cause a striking increase in the proportion of cells resistant to intermediate streptomycin concns. (4-10 [mu]g./ml.). This reached its maximum after 11 generations, and thereafter slowly fell over a period of 50 generations without, however, returning to normal levels.