Association between the Auxogroup of Neisseria gonorrhoeae and the Minimal Inhibitory Concentration of Penicillin

Abstract

The auxogroups and the minimal inhibitory concentrations (MIC) of penicillin for 885 recently isolated strains of N. gonorrhoeae were determined. Auxogroups were established according to the growth requirements of the strains for proline (Pro-), uracil (Ura-), hypoxanthine (Hyx-), citrulline (Cit-) or citrulline replaceable by ornithine (Orn-). The 7 most common auxogroups studied were: Pro-Cit-Ura- (38.8%), Orn-Hyx-Ura- (24.1%), nonrequiring (NR) strains (13.4%), Pro- (9.7%), Orn- (5.2%), Cit-Hyx-Ura- (4.2%) and Pro-Orn-Hyx-Ura- (2.0%). The distribution of MIC of penicillin for the complete set of 885 strains had a bimodal distribution, with a minor peak at 0.01 .mu.g of penicillin/ml and a major one at 0.16 .mu.g/ml. The auxogroups had different patterns of distribution of MIC of penicillin. Five patterns of distribution were found among 8 auxogroups identified. Orn- and NR auxogroups showed a broad distribution of MIC, with a peak at 0.08 .mu.g/ml. Of the Cit-Hyx-Ura- and Orn-Hyx-Ura- auxogroups, > 98% of strains were susceptible to .ltoreq. 0.04 .mu.g of penicillin/ml. All strains of the Pro-Orn-Hyx-Ura- and Pro-Cit-Hyx-Ura- auxogroups were susceptible to .ltoreq. 0.08 .mu.g of penicillin/ml. More than 95% of strains of the Pro-Cit-Ura- auxogroup required .gtoreq. 0.08 .mu.g of penicillin/ml for inhibition of growth. The Pro- auxogroup showed a bimodal distribution, with a major peak at 0.01 .mu.g of penicillin/ml and a minor one at 0.32 .mu.g/ml.