Penicillin class antibiotics have demonstrated varying degrees of in vivo and in vitro success whentested against Chlamydia trachomatis. The activity of ampicillin-sulbactam, an agent commonlyutilized in the treatment of pelvic infections, was tested to ascertain if any antichlamydial activity ispresent. Up to six endocervical isolates of C. trachomatis were tested against each of five antibioticsincluding doxycycline, erythromycin, clindamycin, ampicillin/sulbactam, and sulbactam alone. McCoy cell monolayers were inoculated with high inclusion counts of 10,000–30,000 inclusion-formingunits (IFU) per coverslip, and exposed to each antibiotic. Up to nine subsequent antibiotic freeculture passes were performed to assess the viability of abnormal inclusions. Doxycycline, erythromycin,and clindamycin achieved 100% eradication of inclusions at concentrations of 4.0, 2.0, and1.0 µg/mL. Exposure to ampicillin/sulbactam resulted in a greater than 99% reduction in the inclusioncount at 32.0 µg/mL, while sulbactam by itself demonstrated considerably less activity. Abnormalinclusions were noted only in the ampicillin/sulbactam exposed cells, and these, plus all inclusionsremaining following sublethal exposure to the other antibiotics, resulted in regrowth to controllevels in subsequent passes. Doxycycline and erythromycin demonstrated excellent activity. Clindamycinand ampicillin/sulbactam also significantly reduced inclusion formation, and therefore mayprovide adequate C. trachomatis coverage in patients receiving these antibiotics for pelvic infections.
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