Inhibition of Mycoplasma pneumoniae by actinomycin D.

Growth of Mycoplasma pneumoniae was completely prevented by 0.06 mug of actinomycin D/ml, and 0.00375 mug/ml caused 90% inhibition. It thus appears that M. pneumoniae is more susceptible to actinomycin D than previously reported. Low concentrations (0.019 mug/ml) of the antibiotic primarily inhibited ribonucleic acid synthesis and high concentrations (20 mug/ml) inhibited both ribonucleic and deoxyribonucleic acid synthesis.