Differences in susceptibilities of virulent strains and avirulent strains of Neisseria gonorrhoeae to antimicrobial agents.

Virulent cells (T1 colony type) and avirulent cells (T4 colony type) of Neisseria gonorrhoeae were grown in a defined liquid medium in the presence of different antimicrobial agents. Bacteria of T1 colony type were found to be more resistant than bacteria of T4 colony type to the inhibitory effects of specific concentrations of ampicillin (0.50 mug/ml) and penicillin (0.01 mug/ml). Bacteria of T4 colony type, however, were found to be more resistant to the effects of chloramphenicol (0.40 mug/ml), erythromycin (0.10 mug/ml), spectinomycin (10.00 mug/ml), and tetracycline (0.30 mug/ml). The differences in susceptibilities of these bacteria to the antibiotics investigated were not due to differences in growth rate or to differences in permeability. The data suggest that virulent gonococci and avirulent gonococci have unique properties that affect their susceptibilities to certain antimicrobial agents.