Jen-Yah Hsie, Richard Kotz, Sheldon Epstein
1957 Journal of Bacteriology  
A single carbomycin' requiring colony was noted (Hsie and Kotz, 1955) while working on the development of resistance to carbomycin in a hemolytic, coagulase positive strain of Micrococcus pyogenes var. aureus. The colony was derived from a "second-step" carbomycin resistant mutant and required a minimum concentration of 1,000 ,ug carbomycin/ml nutrient agar to maintain its maximum growth. When lower concentrations of carbomycin were added to the nutrient agar, a smaller number of its progeny
more » ... r of its progeny were able to develop visible colonies. This paper deals with the peculiar morphological and physiological characteristics of the mutant and the "reverse mutation" of the dependent mutant back to the resistant and sensitive character. MATERIALS AND METHODS The stock culture of the carbomycin dependent mutant was originally grown on a nutrient agar (Difco) slant containing 1,000 Mg carbomycin/ml. To conserve the antibiotic, dependent mutants of lower grades were subsequently isolated by subculturing the mutant on gradually decreasing concentrations of carbomycin and selecting the survivors that grew into visible colonies. To estimate the degree of dependency, Szybalski's (1952) gradient plate method was used. Thus a dependent mutant requiring a minimum concentration of carbomycin, 30 Ag/ml, was recovered. This low-grade mutant was employed for the determination of "reverse mutation" rates from the large-sized dependent cells back to cell types displaying carbomycin resistance or carbomycin sensitivity as well as normal staphylococcal morphology.
doi:10.1128/jb.74.2.159-162.1957 fatcat:ltk5fpc5kfdmljsse5ngu72zvq