@article{mbs:/content/journal/micro/10.1099/00221287-20-2-365, author = "Thornley, Margaret J. and Yudkin, J.", title = "The Origin of Bacterial Resistance to Proflavine", journal= "Microbiology", year = "1959", volume = "20", number = "2", pages = "365-372", doi = "https://doi.org/10.1099/00221287-20-2-365", url = "https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-20-2-365", publisher = "Microbiology Society", issn = "1465-2080", type = "Journal Article", abstract = "SUMMARY: Experiments were performed to demonstrate the production in Escherichia coli of spontaneously occurring mutants resistant to proflavine. The fluctuation test of Luria & Delbriick (1943) suggested that such mutants arise. This was confirmed by a modification of the technique of Lederberg & Lederberg (1952). By this method of indirect selection by replica plating, two separate first- step mutants were isolated; from one of these was isolated a second-step mutant, and from this a third-step mutant. The resistance of the third-step mutant was about 100 times greater than that of the original sensitive strain. By the same technique, two first-step mutants to chloramphenicol resistance were isolated. None of the 6 mutants had come into contact with either drug until the time of testing. Crossresistance between proflavine and chloramphenicol was shown by 5 of the 6 mutants; the sixth showed an increase in proflavine resistance though not in resistance to chloramphenicol.", }