Correlation between twitching motility and possession of polar fimbriae in Acinetobacter calcoaceticus

Negatively stained preparations of 16 strains of Acinetobacter calcoaceticus were examined in the electron microscope. Five of the strains did and 11 of the strains did not exhibit twitching motility. Two of the non-twitching strains were substrains of twitching wild-type strains. All twitching strains were found to possess fimbriae with a diameter of approximately 50 A. These fimbriae were shown to be of polar origin except in one strain where, for technical reasons, the origin could not be determined with certainty. Polar fimbriae could not be demonstrated in any of the strains that did not exhibit twitching motility. The demonstration of polar fimbriae was only regularly possible during the exponential growth phase, presumably because the fimbriae are shed by the bacteria during later growth phases. During the study, methods were developed for securing exponentially growing bacteria in concentrations suited for the preparation of negatively stained cells for electron microscopy. Peritrichously arranged fimbriae with a diameter of approximately 30 A were demonstrated in nearly all strains studied, especially on cells in late growth phases. The occurrence of this kind of fimbriae was therefore not correlated with the occurrence of twitching motility.