Multiple Antibiotic Resistance in Clinical Strains of Neisseria gonorrhoeae Isolated in South Carolina

Minimal inhibitory concentration (MIC) values for penicillin G, tetracycline, amoxicillin, and actinomycin D were determined for 81 strains of Neisseria gonorrhoeae isolated from patients attending public health clinics in the Piedmont region of South Carolina. Gonococcal isolates were also screened for highlevel resistance to streptomycin. Significant positive correlations (r >/= 0.45, P </= 0.01) were found between all possible pairs of the antibiotics penicillin G, tetracycline, and amoxicillin. The MIC values of actinomycin D showed no significant positive correlations with the MIC values of the other antibiotics. Gonococcal strains that were resistant to streptomycin tended to be resistant to penicillin G, tetracycline, and amoxicillin. Of the 81 isolates, 18.5% were multiply resistant to penicillin G, tetracycline, amoxicillin, and streptomycin. Spontaneous mutants with reduced antibiotic susceptibility, selected for decreased susceptibility to penicillin G, displayed small decreases in susceptibility to tetracycline, amoxicillin, and actinomycin D. Spontaneous mutants selected for decreased susceptibility to actinomycin D displayed small losses in susceptibility to penicillin G. The results show that multiple antibiotic resistance occurs in clinically isolated gonococcal strains in South Carolina. The results further suggest the presence of a common genetic mechanism determining antibiotic resistance in N. gonorrhoeae.