COMPARATIVE IN-VITRO SUSCEPTIBILITY OF A TETRACYCLINE-RESISTANT CHLAMYDIA-TRACHOMATIS STRAIN ISOLATED IN TOULOUSE (FRANCE)

Background and Objectives: We recently reported the first isolation of a tetracycline-resistant Chlamydia trachomatis strain in Toulouse fro m a woman treated with tetracycline, To characterize this isolate, its in vitro susceptibility was compared with those of 34 other C. tracho matis isolates recovered in Toulouse. Study Design: The susceptibiliti es of C. trachomatis strains were determined in terms of minimal inhib itory concentration (MIC) and minimal bactericidal concentration (MBC) using McCoy cells in 96-well microdilution plates, with an inoculum o f 5.10(3) to 1.10(4) inclusion-forming units/ml. The antimicrobial age nts tested were tetracycline, azithromycin, erythromycin, ofloxacin, a nd pristinamycin. Results: No difference was observed between the MICs and MBCs except for the tetracycline. Tetracycline-resistant strain M IC and MBC were >64 mu g/ml, although <1% of the bacterial population showed resistance. For the other isolates, the MIC of tetracycline was less than or equal to 0.25 mu g/ml. The antibiotics other than tetrac ycline were active in vitro against all strains. Conclusions: These re sults show that the tetracycline resistance observed in Toulouse diffe rs from the ''heterotypic resistance'' described previously in the Uni ted States in multiresistant C. trachomatis isolates. They confirm tha t the resistance we observed may be a new phenomenon.