Susceptibility of penicillinase-producing and non-penicillinase-producing strains of Neisseria gonorrhoeae isolated in Durban, South Africa, to 15 beta-lactam antibiotics.

Using two different inoculum sizes (10(4) and 10(7) organisms), we tested 35 penicillinase-producing (PPNG) and 72 non-PPNG strains of Neisseria gonorrhoeae falling into three categories (penicillin-sensitive, intermediately resistant, and resistant) by the agar-dilution method against 15 beta-lactam antibiotics. With the exception of penicillin, ampicillin, amoxicillin, and cephradine, the isolates were uniformly sensitive to all the other antibiotics tested (including spectinomycin, tetracycline, rosoxacin, sulfamethoxazole-trimethoprim [19:1 ratio], and kanamycin). Ceftriaxone and cefotaxime were the two most active compounds tested; all strains were inhibited at concentrations of 0.007 and 0.015 microgram/ml, respectively. Isolates with intrinsic resistance to penicillin were less susceptible to cefoxitin and cefuroxime than were PPNG strains. The effect of inoculum size varied for the different antibiotics; penicillin and cefaclor showed this effect only with PPNG strains, whereas for ampicillin and amoxicillin it was also seen with non-PPNG strains. Cephamandole showed this effect with both penicillin-sensitive and PPNG strains. In view of the increasing resistance to penicillin, we would recommend that alternative drugs be used as first line therapy for gonorrhea in South Africa.