Abstract

Culture samples of Neisseria gonorrhoeae and Escherichia coli were studied by transmission and electron microscopy to evaluate the effect of different preparation procedures on the pilation of these organisms. Unfixed as well as fixed bacteria showed only few, long, filamentous appendages when investigated in ultrathin sections, negatively stained specimens, or critical-point dried preparations. Snap-frozen specimens of E. coli showed many short and thin pili after being shadowed with carbon and platinum whereas those of N. gonorrhoeae showed only some type-C-like pili. Thus, the number and morphological appearance of pili appear to be greatly influenced by the preparation techniques used for study by electronmicroscopy. Conclusions as to the type and the infectivity of a bacterial strain can, therefore, not be based on purely morphological criteria.