In vitro susceptibility and cross-resistance of South African isolates of Neisseria gonorrhoeae to 14 antimicrobial agents.

One hundred isolates of Neisseria gonorrhoeae obtained from patients attending clinics in Johannesburg, South Africa, were tested by a broth dilution technique for their minimal inhibitory concentrations (MICs) of benzyl penicillin G, ampicillin, cefoxitin, cefuroxime, cefotaxime, ceftriaxone, ceftazidime, tetracycline, minocycline, doxycycline, spectinomycin, rosaramicin, chloramphenicol, and rosoxacin. None of the isolates tested produced beta-lactamase. The MICs of penicillin ranged from less than or equal to 0.007 to 0.5 micrograms/ml. The isolates were also very susceptible to rosaramicin (minimal concentration at which 50% of isolates were inhibited [MIC50] = 0.02 micrograms/ml) and to the new cephalosporins (cefotaxime MIC50 less than 0.007 micrograms/ml, ceftriaxone MIC50 less than 0.007 micrograms/ml, and ceftazidime MIC50 less than 0.007 micrograms/ml). By using regression analysis, good correlation was observed between the MICs of penicillin and those of the other agents, with the exception of ceftriaxone, spectinomycin, and rosaramicin. The MICs and the minimal bactericidal concentrations were within a log2 concentration of each other.