The electron microscope provides the microbiologist with unparalleled resolution and magnification. It is the tool of choice when studying the intimate details of bacteria and the environments which they inhabit. There are two distinct types of electron microscopy (EM): transmission (TEM) and scanning (SEM) electron microscopy. In both types of electron microscopy, a stream of electrons is emitted from a source and bent by magnets to focus the electron beam (just as light is bent by glass lenses).

But this powerful tool must be used carefully! The incredible magnification and resolving power does not come without a price (in addition to the monetary expense). To be viewed under an electron microscope, samples must be treated with fixatives and other stains that may alter the surface or structure of the cell. This fixation often causes artifacts to apear on or around the cell, which can lead to inaccurate interpretation of the final images.

Transmission Electron Microscopy


The transmission electron microscope is an essential tool for the structural microbiologist. The high resolving power of the microscope allows scientists to the examine cell structures such as the cell membrane and wall. Even nucleic acids and viruses can become visible within the transmission electron microscope.

For transmission electron microscopy, the specimens are imbedded in a plastic and cut in very very thin slices (.150 um thick). Electrons are emitted from a source and pass through the thin-sectioned specimen. This gives TEM's the ability to show us the inside of some very small microorganisms. The transmitted_ electrons form an image which is interpreted by a computer and viewed readily on a screen.



Scanning Electron Microscopy

The scanning electron microscope is useful for obtaining 3-dimensional images of specimens. The sample is coated with a thin layer of electron-rich material, such as gold/palladium. The electron beam scans back and forth across the surface of the cell. The electrons are scattered by the gold surface, and collected by a detector that interprets the data to produce a 3-dimensional image. Samples can be magnified up to 500,000 times with a resolution limit near 1 nm. With the scanning electron microscope, surface structures of microorganisms can be observed as well as total cell morphology.