[Susceptibility to macrolides against Mycoplasma pneumoniae isolated during 7 years]

The efficacies of macrolide antibiotics, rokitamycin, leukomycin, josamycin and erythromycin were investigated against 63 strains of M. pneumoniae included FH strain which were isolated from clinical specimens obtained in 1986-1987, 1991, 1992-1993. Values of MICs and MBCs of these antibiotics were evaluated by two methods, broth dilution method and M. pneumoniae L cell infection system. In broth dilution method, MIC50 and MBC50 of rokitamycin were 0.0063-0.025 microgram/ml and 0.025-0.2 microgram/ml respectively. The ratios of MBC50/MIC50 were 1-32. MIC50 of leukomycin, josamycin and erythromycin were 0.0063-0.05 micrograms/ml, 0.0025-0.05 microgram/ml, and 0.0125-0.05 microgram/ml respectively. MBC50 of these drugs were 0.0125-50 micrograms/ml, 25-50 micrograms/ml, and 25-50 micrograms/ml respectively. The ratios of MIC50/MBC50 were 2-800, 500-2000, 500-4000. MIC50 of rokitamycin and leukomycin to the isolates during period from 1992-1993 were higher as compare to those of isolates during 1986 to 1991. On the other hand, rokitamycin markedly reduced the numbers of CFU in the growth phase when added at the concentrations of 16 and 4 times the MIC, but the other macrolides were reduced slightly CFU at the concentrations of 4 times, the MIC. In L cell infectious system, MIC50 and MBC50 of rokitamycin were 0.005-0.0125 microgram/ml and 0.05-0.1 microgram/ml respectively. The ratios of MBC50/MIC50 were 1-2 Ratios of leukomycin, josamycin, and erythromycin were 0.05-0.1 microgram/ml, 0.05-0.2 microgram/ml and 0.050-0.1 microgram/ml respectively. The MBC50 of these drugs were 0.2-0.4 micrograms/ml, 0.8-1.6 microgram/ml, 0.8-1.6 microgram/ml. Ratios of MBC50/MIC50 were 2-8, 4-32, 8-32.(ABSTRACT TRUNCATED AT 250 WORDS)