CHLAMYDIA TRACHOMATIS: IN VITRO SUSCEPTIBILITY TO ANTIBIOTICS SINGLY AND IN COMBINATION

Decreased susceptibility in vitro to erythromycin has been demonstrated for few C. trachomatis isolates outside Scandinavia, making local susceptibility‐screening indicated. Eleven recent isolates of C. trachomatis found in a Danish hospital have been examined for susceptibility, expressed as minimal inhibitory concentration (MIC) to antibacterial agents commonly used in genito‐urinary infections. Full susceptibility to doxycycline and erythromycin was demonstrated. Clindamycin and ampicillin showed moderate activity, and sulfamethizole had a MIC value in the border area of what is needed for therapeutic effect in non‐urinary infections. C. trachomatis, being a major pathogen in pelvic inflammatory disease, makes combination chemotherapy desirable in order to protect against resistance development, to obtain synergistic effect and to ensure effect in infections of mixed etiology – provided antagonism could not be anticipated. In three checkerboard trials, with the combinations doxycycline plus ampicillin, erythromycin plus sulfamethizole and ampicillin plus sulfamethizole, using MIC as end‐point, neither synergism nor antagonism could be demonstrated in the concentration range from 1/8 to 4 times the MIC values of each drug. 1986 Acta Pathologica, Microbiologica et Immunologica Scandinavica