Effects of Several Macrolide Antibiotics on Mycoplasma pneumoniae

Susceptibilities of 50 strains of M. pneumoniae which were isolated from acute respiratory infectious diseases, to several macrolide antibiotics were investigated by two methods. One is the agar dilution method, the other is M. pneumoniae L cell infection system.The minimum inhibitory concentrations (MICs) of erythromycin (EM) and new macrolide, rokitamycin (RKM), which inhibit the growth of 75% strains of the microorganisms tested were 0.007μg/ml. The MICs of josamycin (JM) and kitasamycin (leucomycin, LM) were 0.015μg/ml and 0.03μg/ml respectively.The minimum concentrations of EM which eliminate the microorganisms from L cells were not proportional to the MICs obtaind by the agar dilution method. The doses of EM for eliminations of several strains of microorganisms were more than ten times high in comparing with their MICs. In contrast, the doses of RKM, JM and LM for the elimination coinside essentially with their MICs. Also we confirmed by DNA staining method that the particles of M. pneumoniae which adhered on the surface of L cells could be eliminated after treatment of RKM.