Comparative study of minimal inhibitory concentration (MIC) and minimal lethal concentration (MLC) values for tetracycline, monocycline, erythromycin and rokitamycin against eleven strains of Chlamydia trachomatis

Abstract

In vitro activity of the 3 antimicrobial agents, against 18 recent isolates of Chlamydia trachomatis: 11 from urethral samples and 7 from endocervical samples, was tested by cell culture technique. HeLa 229 cells maintained in antibiotic-free MEM medium supplemented with 10% fetal calf serum and 2 mM glutamine were seeded into 96-well culture plates. After inoculation with 10(2) to 10(3) inclusion-forming units/ml of each strain of C. trachomatis, the culture medium was replaced by a maintenance medium containing 1 micrograms/ml of cycloheximide and serial two fold dilutions of the antibiotics. After 48 h incubation at 36 degrees C in 5% CO2 atmosphere, cells were fixed and inclusion bodies were stained using fluorescein-conjugated anti-Chlamydia monoclonal antibodies. MICs were defined as the lowest antibiotic concentrations required to inhibit the development of a single inclusion. MICs 90% (mg/l) were 0.054 for doxycyclin, 0.700 for ofloxacin and 0.150 for erythromycin. These results confirm the effective in vitro activity of the three antibiotics tested against C. trachomatis.