Submitted to: Texas Society for Electron Microscopy Journal
Publication Type: Abstract Only
Publication Acceptance Date: 10/24/2002
Publication Date: N/A
Technical Abstract: Washed and unwashed overnight cultures of Salmonella typhimurium were examined for the expression of fimbriae using negative stain. In the course of the evaluation, it was noted that the distribution of bacteria on formvar coated grids was dependent on the negative stain utilized for visualization. With phosphotungstic acid, bacteria tended to aggregate along the grid bars on both carbon coated and uncoated formvar grids. Aggregation of bacteria hindered the observation of individual bacteria for the determination of fimbrial expression. Alteration of stain concentration and pH did not effectively enhance the distribution of bacteria on the grid. Several surface tension modifiers -- poly-L lysine, bovine serum albumin and bacitracin -- as well as glow discharge, were able to slightly improve bacterial distribution. However, in the case of protein modifiers the appearance of protein molecules in the background interfered with the observation of expressed fimbriae. Staining of bacteria with either 1 or 0.5% aqueous ammonium molybdate produced grids with evenly spread bacteria with a relatively clean background. Inclusion of protein surface tension modifiers did not enhance the distribution of bacteria but did contribute unnecessary background to the images. Staining bacteria with aqueous uranyl acetate produced grids with bacteria more evenly distributed than with phosphotungstic acid. However, grids stained with uranyl acetate had lower numbers of attached bacteria than when stained with ammonium molybdate. In the case of S. typhimurium, ammonium molybdate proved to be a superior stain for the visualization of fimbriae. Its superiority was due to its ability to produce grids with evenly stained and distributed bacteria without the need for surface tension modifiers.