Protein I serotype of serum-resistant versus serum-sensitive Neisseria gonorrhoeae strains.

In order to characterize serum-resistant and serum-sensitive strains of N. gonorrhoeae, the protein I serotype, auxotype, and penicillin susceptibility of 128 strains were tested. Sensitivity to the complement-dependent bactericidal activity of normal human serum was highly associated with protein I serotype (p less than 0.001). Thus 85% of serotype 1-3 strains were serum-resistant, whereas 86% of serotype 8 strains and all strains with serotypes 8 + 9 or 9 were serum-sensitive. Serum-resistance or sensitivity for a given serotype was independent of auxotype. The susceptibility to penicillin within the serotypes 1-3 was significantly associated with auxotype (p = 0.0016); all AHU- (requirement for arginine, hypoxanthine and uracil) strains had MICs of penicillin of 0.04 microgram/ml or less and were serotypes 1-3. Among the non-AHU-strains, serotype 9 was significantly more penicillin susceptible than the other serotypes (p less than 0.003).