GROWTH COMPARISONS OF STREPTOMYCIN-SENSITIVE AND STREPTOMYCIN-RESISTANT MICROCOCCUS PYOGENES VAR. AUREUS

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Abstract
A significant difference in growth of the sensitive parent and streptomycin-resistant mutants of M. pyogenes var. aureus in the semi-synthetic medium of Frieden and Frazier was detected. The sensitive parent could initiate growth and grow on continued subculture; however, growth was always sparse. The resistant mutants, on the other hand, grew excellently in the same medium under the same conditions. Additions of biotin to the semi-synthetic medium stimulated growth of the sensitive organism to a level comparable with the resistant mutants. Evidence is offered for the mutational origin of resistant bacteria. One culture (out of 121 attempts), obtained in the absence of streptomycin by a screening method, produced much heavier growth than the usual culture in the semi-synthetic medium. This culture was found to be resistant to at least 1000 U./ml. of streptomycin.