In vitro susceptibility of Neisseria gonorrhoeae to nine antimicrobial agents

Abstract

The in vitro action of nine antibiotics was tested by the agar streak method against 45 gonococcal strains isolated from penicillin-therapy failures. The penicillin susceptibility range of these strains was 0.003 to 1.32 mug/ml, and the tetracycline susceptibility range was 0.125 to 2.0 mug/ml. Minimal inhibitory concentrations of minocycline and doxycycline paralleled the activity of tetracycline and ranged from 0.125 to 1.0 mug/ml and 0.125 to 2.0 mug/ml, respectively. Rifampicin, with a narrow range of 0.5 to 1.0 mug/ml, inhibited 75% of the strains at 0.5 mug/ml. The range for cephaloridine and cephaloglycine was 0.5 to 20.0 mug/ml, but another cephalosporium derivative, cephalexin, exhibited greater activity in its range of 0.25 to 20.0 mug/ml. A semisynthetic penicillin, carbenicillin, with a range of 0.025 to 0.75 mug/ml, displayed more activity against the lower susceptible penicillin G gonococcal strains.