In vitro evaluation of minimum inhibitory concentration of several antibacterial agents against Rickettsia japonica using a plaque reduction assay system.

The study was conducted to determine the minimum inhibitory concentrations (MICs) of several antibacterial agents against Rickettsia japonica, which causes Japanese spotted fever. A plaque reduction assay as an in vitro culture method was conducted to determine the MICs of antibacterial agents (4 types of tetracyclines: tetracycline, doxycycline, minocycline, and tigecycline; 3 types of quinolones: ciprofloxacin, ofloxacin, and levofloxacin; and 2 types of macrolides: azithromycin and clarythromycin) against R. japonica. R. japonica was sensitive to the antibacterial agents tested with MICs similar to those against other spotted fever rickettsia determined in previously described plaque reduction assays.