Arrangement of pili in colonies of Neisseria gonorrhoeae

The morphology and arrangement of pili in the P++ colony phenotype of Neisseria gonorrhoeae were examined by a variety of electron microscopic techniques. The apparent structure and organization of gonococcal pili varied depending upon the method of specimen preparation. Pili as thin, individual, unbranched structures were demonstrated by negative staining and in sections of epoxy-embedded specimens. Pili forming thick structures which branch, subdivide, and rejoin to form an irregular lattice were demonstrated in specimens processed by the critical-point drying method and by rapid freezing and low temperature sublimination. We propose that in gonococcal colonies of the P++ phenotype, pili exist as individual threadlike structures only on the bacterial surfaces; as the pili leave the bacterial surfaces, they form thick bundles which branch, subdivide, and rejoin to form a supporting framework interconnecting the colony members. This arrangement of pili is usually disrupted by the commonly used method of negative staining and cannot be clearly detected within epoxy-embedded specimens. These data are summarized in a model depicting the organization of pili in the P++ colony phenotype of N. gonorrhoeae.