Resistance of Neisseria gonorrhoeae to phagocytosis: relationship to colonial morphology and surface pili

Strains of Neisseria gonorrhoeae colonial types that are known to be associated with virulence for humans exhibited greater resistance to phagocytosis by human peripheral leukocytes than did avirulent types of N. gonorrhoeae. When variants of types 1 and 4, derived from the same clinical isolate, were tested repetitively, the mean percentages of phagocytosis were 8.6% and 59.1%, respectively. Resistance to phagocytosis and surface pilation of colonies of types 1 and 2 could be preserved by selective subculture. On nonselective subculture, there was a simultaneous decline in (I) percentage of colonies in the virulent phase, (2) proportion of gonococci exhibiting pili under the electron microscope, and (3) resistance to phagocytosis. Rabbit antiserum to type 2 gonococcal colonies enhanced phagocytosis of gonococci derived from virulent colonial types. These results demonstrate that the surfaces of colonial types 1 and 2 of N. gonorrhoeae have antiphagocytic properties and suggest that these properties may be associated with surface pili.