Classification of Microorganisms

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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
Domain Eukarya
• 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
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
Serology
• Combine known
antiserum + unknown
bacterium or bacterial
antigens
• Slide agglutination
• ELISA
• Western blot
Another antibody-antigen test
• Rapid “Strep” throat test
• Detects Group A streptococci (i.e. Streptococcus
pyogenes) in minutes.
Copyright © 2004 Pearson Education, Inc., publishing as Benjamin Cummings
Flow Cytometry
• Can identify different cell
types
• Fluorescently labelled
antibodies are attached to
cells
• Computer detects cells
Genetics
• DNA fingerprinting
• Electrophoresis of
enzymatic digests
• rRNA sequencing
Nucleic Acid Hybridization: DNA chip
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