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Sixty strains of Neisseria gonorrhoeae have been classified into four main groups according to their resistance to killing by human complement together with either normal human or immune rabbit antibodies. The rabbit antisera had been raised against 10 of the strains tested. The normal human antibodies had probably been formed against cross-reacting organisms since they could be removed by absorption with N. pharyngis sicca, N. pharyngis flavus, N. catarrhalis, or Escherichia coli. Bactericidal antibodies could be absorbed from both normal and immune sera by N. gonorrhoeae which had been autoclaved or trypsinized, and by red cells coated with gonococcal lipopolysaccharides. The results suggest that the antigens involved in the bactericidal reaction are lipopolysaccharides of several distinct specificities. Since individual sera always reacted more widely in hemagglutination than in bactericidal tests, it is postulated that surface-blocking antigens may restrict access to the lipopolysaccharides in the intact organisms.

Red cells coated with lipopolysaccharides from three different strains of Neisseria gonorhoeae have been used as antigens in a haemagglutination test for gonococcal antibodies. For each strain the geometric mean titre in sera from 50 male and 25 female patients was significantly higher than that in 50 normal controls. The most useful smooth strain, G1, picked out 84% of females and 46% of males from a group of patients known to have gonorrhoea, but only gave 2% positives among controls. The rough strain, G2, gave 10% positives in controls and 31% in patients. The results suggest that the method is worth developing further as a diagnostic test and that strain differences are important. False positives were probably due to cross-reacting antibodies.

Gonococci suspended in 1% proteose peptone containing 8% glycerol can be snap frozen in liquid nitrogen without detectable loss on thawing. This recovery rate has allowed the use of frozen organisms as the starting inoculum for the bulk growth of gonococci and to preserve gonococci both in urethral pus and after primary subculture for use in studies on gonococcal virulence. The method described for freezing urethral pus on charcoal swabs should make it possible to transport infected specimens from areas lacking adequate laboratory facilities.