Coagglutination as a test for Neisseria gonorrhoeae

After growth on Thayer-Martin medium, 196 strains of freshly isolated Neisseria gonorrhoeae were subjected to a coagglutination reaction. The sensitivity of the test was 94% and did not vary much in the hands of four consecutive technicians. In a group of 99 strains tested by one of the technicians non-interpretable results were obtained with 17% of the strains when the test was performed with cells taken from the first or primary plate, against 9% when cells from the secondary (subcultured) plate were used. The lowest number of non-interpretable results was found with a modified Thayer-Martin medium, which also showed the lowest number of false negatives (2%).No non-interpretable results were obtained when the bacterial suspension was first heated to 100°C for 3 min. In a group of 14 recently isolated strains of non-gonococcal species there was only one, preventable, false-positive strain and there were none in a group of 12 meningococci (all of them laboratory strains).In comparison with the fermentation test with Lingelsheim's sugars, the coagglutination test with cells taken from the primary plate with Thayer-Martin medium yielded a conclusive result more often. The test is simple and rapid and does not require special technical equipment. It seems to deserve a place as a confirmative test in the search for gonococci in samples from the urogenital-anal area.