Classification of Microorganisms – Chapter 9

• Taxonomy

• The science of classifying organisms

• Provides universal names for organisms

• Provides a reference for identifying organisms

• Phylogeny

• The study of the evolutionary history of organisms

The Three-Domain System

Taxonomic Hierarchy

Species Definition• Eukaryotic species:

• A group of closely related organisms that breed among themselves and produce offspring that can produce offspring

• Viral species:

• Population of viruses with similar characteristics that occupies a particular ecological niche

• Prokaryotic species:• A population of cells with similar characteristics

•Based on:•morphology

•biochemistry

•genetics

Strain: Genetically different cells within a species

• Animalia: Multicellular; no cell walls; chemoheterotrophic

• Plantae: Multicellular; cellulose cell walls; usually photoautotrophic

• Fungi: Unicellular or multicellular; cell wall structure varies; Chemoheterotrophic

• Protista: A catchall for eukaryotic organisms that do not fit other kingdoms; Predominantly unicellular

Domain Eukarya

References

•• Bergey’s Manual of Determinative Bacteriology

•Provides identification schemes for identifying bacteria and archaea

•Morphology, differential staining, biochemical tests

•• Bergey’s Manual of Systematic Bacteriology

•Provides phylogenetic information on bacteria and archaea

•Based on rRNA sequencing

•• Approved Lists of Bacterial Names•Lists species of known prokaryotes

•Based on published articles

Identification Methods• Morphological characteristics: More useful for

identifying eukaryotes than prokaryotes

• Differential staining:

• Gram staining

• Acid-fast staining

• Special staining

• Negative staining

• (Endo)spore staining

Identification Methods

• Biochemical tests:

• Determines presence of specific bacterial

See Animations → Dichotomous Key (chapter 10 Microbiology Place CD or website)

Miniaturized Rapid Identification – “Enterotube”

Vitek 2 – a more advanced miniaturized rapid identification system

• Combine known antiserum + unknown bacterium or bacterial antigens

• Slide agglutination

• ELISA

• Western blot

Serology

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Another antibody-antigen test

• Rapid “Strep” throat test

• Detects Group A streptococci (i.e. Streptococcus pyogenes) in minutes.

• Can identify different cell types

• Fluorescently labelled antibodies are attached to cells

• Computer detects cells

Flow Cytometry

• DNA fingerprinting

• Electrophoresis of enzymatic digests

• rRNA sequencing

Genetics

Nucleic Acid Hybridization: DNA chip