Sixty four penicillinase-producing Neisseria gonorrhoeae (PPNG) and 24 non-penicillinase-producing (non-PPNG) strains isolated from six different south east Asian localities were tested by the agar dilution method against 15 antibiotics. All isolates were susceptible to spectinomycin and sulphamethoxazole-trimethoprim (19:1 ratio). A large proportion of both PPNG and non-PPNG strains showed, however, a decreased susceptibility to tetracycline, kanamycin, and erythromycin: 49% with minimum inhibitory concentrations (MICs) of tetracycline greater than or equal to 2 micrograms/ml, 34% with MICs of kanamycin greater than or equal to 32 micrograms/ml, and 80% with MICs of erythromycin greater than or equal to 2 micrograms/ml. These MIC cut-off values were chosen since they are close to the highest concentrations of these antibiotics attainable in serum after drug administration. Resistance to these antibiotics was not related to penicillinase production and does not appear to be confined to gonococci isolated from one particular locality. Strains showing resistance concurrently to two or three of these drugs were often isolated from different south east Asian countries. All eight cephalosporins tested were effective against both PPNG and non-PPNG strains. On a weight to weight basis the new cephalosporins--namely, moxalactam, cefoperazone, cefotaxime, and ceftriaxone--were the most effective. In contrast to those of cefoxitin, cefuroxime, moxalactam, and cefoperazone the MICs of cefamandole, cefotaxime, and ceftriaxone were significantly affected when the inoculum size was increased from 10(3) to 10(6) colony forming units (cfu).
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