Resistance of Mycoplasma pneumoniae to macrolide and analogous antibiotics.

1. The susceptibility of M. pneumoniae to antibiotics can be determined by the microtiter method. The adequate technique requires that the final volume of broth medium in a well is 0.2 ml and that the dilution is made after the parent solution of antibiotic in the test tube is dropped into a well every fifth wells. 2. M. pneumoniae was cultured on agar media containing two-fold concentrations of macrolide and analogous antibiotics, and the following results were obtained. 1) The growth of eight strains of M. pneumoniae on agar media containing two-fold concentrations of the antibiotics revealed that, in six strains, one CFU (colony forming unit) per 10(5) to 10(6) CFU of an inoculum dose was resistant to the antibiotics. 2) The MIC (minimum inhibitory concentration) of erythromycin for the subculture of thet strains of M. pneumoniae on agar media containing two-fold concentrations of the antibiotics revealed that, in six strains, one CFU (colony forming unit) per 10(5) to 10(6) CFU of an inoculum dose was resistant to the antibiotics. 2) The MIC (minimum inhibitory concentration) of erythromycin for the subculture of thet strains of M. pneumoniae on agar media containing two-fold concentrations of the antibiotics revealed that, in six strains, one CFU (colony forming unit) per 10(5) to 10(6) CFU of an inoculum dose was resistant to the antibiotics. 2) The MIC (minimum inhibitory concentration) of erythromycin for the subculture of the colony grown as an average of 0.5 to eight on agar media containing erythromycin in four strains was 0.1 to 1.6 micrograms/ml in some colonies, and 400 to 800 micrograms/ml in most colonies. The results disclosed that the broth culture contains a small number of mycoplasma cells with a definite, high degree of resistance to the antibiotics, but no cells with intermediate degrees of resistance. 3) The FH strain was made resistant to erythromycin, oleandomycin, midecamycin, acetylspiramycin, leucomycin, josamycin, tylosin, lincomycin, or clindamycin by subculture in broth medium from the colony grown at the highest concentrations of each of the antibiotics in agar media. The degree of the resistance developed was 16 to 128,000 in the MIC radio and showed high values of MIC in most strains. The resistance developed was not lost by subculturing the resistant strain in broth medium without antibiotic. 4) The FH strain made resistant to the antibiotics had cross resistance to other macrolides. Strains resistant to some of the antibiotics had cross resistance to lincomycin and clindamycin, and strains resistant to others did not. Some strains made resistant to macrolides with cross resistance to lincomycin and clindaymycin and strains made resistant to lincomycin or clindamycin had no cross resistance to vernamycin B alpha, while all the resistant strains without cross resistance to lincomycin and clindamycin had cross resistance to vernamycin B alpha. No strain had cross resistance to vernamycin A...