Electron Microscopy

Principles


In electron microscopy, samples are visualized by bombarding them with a stream of electrons, (instead of light rays), which are bent and focused with magnetic beams.   Because electrons are so small, electron microscopes can easily resolve images at the level of nanometers. Contrast is provided by a variety of electron rich, heavy metal stains such as osmic acid, permanganate, or uranium. Transmission electron microscopy allows examination of the inside of organisms. Specimens must be sliced into thin sections, then stained.

Procedure

  1. Inoculate clinical specimens onto cell culture lines.
  2. Observe daily for cytopathic effects
  3. Prepare tissue culture samples that showed cytopathic effects for electron microscopy by drying the sample.
  4. Wash and stain the samples
  5. Embed in epoxy resin and slice into thin sections for viewing under electron microscope

Advantages

  • Preparation is simple and fast
  • Can be applied to a number of different body samples
  • It provides an "open" view for previously unidentified pathogens; does not depend on specific interactions with known molecules

Disadvantages

  • Not suitable for screening large numbers of samples

  • Low pathogen load may hinder identification
 

Examples

Negative stain TEM of rotavirus
TEM of Gram (+) bacterial cell