In vitro activity of beta-lactam drugs and sulbactam against Chlamydia trachomatis

We tested the in vitro activity of ampicillin, ampicillin-sulbactam, cefoperazone, cefoperazone-sulbactam, and sulbactam against 18 recent clinical isolates of Chlamydia trachomatis and two ATCC strains. Ampicillin (MIC50, 256 micrograms/ml) and sulbactam (MIC50, 128 micrograms/ml) demonstrated some activity against C. trachomatis, but cefoperazone had little to no activity. At 2-3 dilutions below the MIC, C. trachomatis treated with ampicillin or sulbactam, but not cefoperazone, formed small inclusions that remained small on passage onto antibiotic-free McCoy cells. It appears that ampicillin and sulbactam suppress rather than kill C. trachomatis.