STUDIES ON A METHOD FOR EVALUATING THE IN VITRO ACTIVITIES OF ANTIMICROBIAL AGENTS AGAINST CHLAMYDIA TRACHOMATIS

Abstract

A method for determining the activities of antimicrobial agents against Chlamydia trachomatis was evaluated, because a standard method of this field has not been yet obtaine.
The D/UW-3/Cx strain, one of the prototype strains of C. trachomatis was inoculated onto HeLa 229 cells and was cultured in 24-well dish at 37°C for 48 hours. The culture medium was MEM with 10% of fetal bovine serum and contained various concentrations of antimicrobial agents immediately after inoculation of C. trachomatis. The inclusion bodies were detected by the method of direct immunofluorescence staining, using FITC-labelled anti-C. trachomatis monoclonal antibody and were confirmed by electron microscopy in some cases. The minimum inhibitory concentration (MIC) was defined as the lowest concentration of antimicrobial agent preventing the appearance of any inclusion bodies of C. trachomatis.
An optimum inoculum of C. trachomatis was 5-10³ inclusion forming units per well, because a larger dose of inoculum tended to see aggregation of the organisms, and a smaller dose resulted in a difficulty of observation.
The MICs of tetracycline, minocycline and erythromycin against D/UW-3/Cx strain of C. trachomatis were 0.01, 0.02 and 0.08μg/ml, respectively. The MIC of ofloxacin, a new pyridone carboxylic acid, was 0.64μg/ml.
In conclusion, this method was useful for evaluating the susceptibility of C. trachomatis to antimicrobial agents.