Topic 19: Unknown Identification and Bergey's Manual

• 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.

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