A pure culture contains only one species or type of microorganism. A mixed culture contains two or more KNOWN species. A contaminated culture contains both known and unknown (unwanted) microorganisms.

Individual microbial colonies originate from single microbial cells.

Most microorganisms can be cultured on artificial media, but some can be cultured only in living tissue.

Artificial media are classified by their physical content as either liquid, semisolid, liquefiable solid, and nonliquefiable solid.

Artificial media are classified by their chemical content as either synthetic, or nonsynthetic depending on if the chemical composition is known.

Artificial media are classified by their function as either general purpose media or media with one or more specific purposes. Enriched, selective, differential, transport, assay, and enumerating media are all examples of media designed for specific purposes.

Incubation, Inspection, Identification
Microorganisms are identified in terms of their macroscopic or colony morphology, their microscopic morphology, and their biochemical reactions.

Maintenance and disposal of cultures
Microbial cultures are disposed of in one of two ways: steam sterilization or incineration.

The Microscope: Window on an Invisible Realm
Magnification, resolving power, lens quality, and illumination source all influence the clarity of specimens viewed through the optical microscope.

The maximum resolving power of the optical microscope is 200nm or 0.2 um. This is sufficient to see the internal structures of eucaryotes and the morphology of most bacteria.

There are 5 types of optical microscopes. Four types use visible light illumination: bright field, dark field, phase-contrast, and interference microscopes. The fifth type, the fluorescence microscope, uses UV light for illumination, but it has the same resolving power as the optical microscopes.

Electron microscopes use electrons, not light waves, as an illumination source to provide high magnification (100 x 10⁶ X) and high resolution (0.5 nm). Electron microscopes can visualize cell ultrastructure (TEM) and 3-D images of cell and virus surface features (SEMs).

Specimens viewed through optical microscopes can be either alive or dead, depending on the type of specimen preparation, but all EM specimens are dead because they must be treated with metals for effective viewing.