Most bacteria are identified through evaluation of primary characterisitics such as morphology and growth patterns and secondary characterisitics such as metabolism and serology.

Characterisitics that is critical for distinguishing one bacterial group from another may be irrelevant for identification of other bacteria.

Bergey’s Manual

• bacteria are classified according to similarities in their ribosomal RNA (rRNA)

• includes domains bacteria and archaea

• similar rRNA sequences are grouped together into taxa

• taxa used for bacteria and archaea are phylum, class, order, family, genus, and species

dichotomous classification system - a population is repeatedly divided into two parts until a description identifies a single member

• aka “artifical key” since no single correct way to write one

Check conclusion of bacterium with the species description given in Bergey’s Manual

To begin identification, ascertain the purity of the culture you have been given and prepare stock and working cultures

• avoid contamination of your unknown

• note growth characterisitics and gram stain appearance for clues about how to proceed

• after culturing and staining the unknown, many bacterial groups can be eliminated

• final determination of unknown bacterium will depend on carefully selecting the relevant biochemical tests and weighing the value of one test over another in case of contradictions.