[Study of bactericidal effect of the spiramycin and minocycline on Mycoplasma pneumoniae].

This study was designed to determine if the inhibitory effect of a macrolide (spiramycin) and a tetracycline (minocycline) on the in vitro growth of Mycoplasma pneumoniae is due to a bacteriostatic or a bactericidal activity. M. pneumoniae, strain FH-Liu, susceptible to spiramycin and minocycline was exposed to various inhibitory concentrations of these antibiotics (within the range of 0.5-32 mg/l) for various periods of time (1-9 days). The bactericidal activity was determined by subculturing material from tubes using serial dilution. Spiramycin was bactericidal after 4 days (greater than or equal to 3 log10 decrease of the inoculum) only when high concentrations were used (16 mg/l). Minocycline was bactericidal after 4 days at a concentration of 32 mg/l. These results show a 64-fold difference between minimum inhibitory concentration and minimum bactericidal concentration for spiramycin and a 128-fold difference for minocycline. Our data confirm the bacteriostatic effect of these drugs on M. pneumoniae.