Inhibition of Neisseria gonorrhoeae by normal human saliva

Saliva was found to be a powerful and specific inhibitor of Neisseria gonorrhoeae. Although 28 other species of bacteria were tested, including Neisseria meningitidis, Neisseria pharyngis var flava, Neisseria lactamica, and Neisseria catarrhalis, we failed to find any others sensitive to saliva under similar conditions. The physical properties of the inhibitory substance indicated that it might be salivary alpha-amylase. To test this hypothesis alpha-amylase was extracted from saliva and was shown to have a high antigonococcal activity. Hog pancreas alpha-amylase also showed strong antigonococcal activity, thus the observations indicate that for the strains we tested alpha-amylase is inhibitory to gonococci. This observation indicates that either the gonococcal outer cell wall contains some unique lipopolysaccharides or that the gonococcus is unusually dependent on the integrity of these moieties. Whichever speculation proves to be true it indicates a need for a careful study of the gonococcal cell wall.