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Chapter 4
Microscopy, Staining, and Classification
6/30/11 MDufilho
Classification and Identification of Microorganisms
– Taxonomy consists of classification, nomenclature, and identification
– Organize large amounts of information about organisms
– Make predictions based on knowledge of similar organisms
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Classification and Identification of Microorganisms
• Linnaeus and Taxonomic Categories– Linnaeus
– Classified organisms based on characteristics in common
– Organisms that can successfully interbreed called species
– Used binomial nomenclature in his system– Linnaeus proposed only two kingdoms
© 2012 Pearson Education Inc.
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l. scapularis (deer tick)
l. pacificus (black-eyed tick)
l. ricinus (castor bean tick)
Parasitiformes (mites and ticks)
Acariformes (mites)
Rhipicephalus
Ixodidae (hard ticks)
Dermacentor Ixodes
Argasidae (soft ticks)
AraneidaScorpionida
ArachnidaCrustaceaInsecta
Chordata (vertebrates)
Arthropoda (joint-legged animals)
Platyhelminthes (tapeworm)
Nematoda(unsegmented roundworms)
Animalia Plantae Fungi
Bacteria Archaea Eukarya
Family
Class
Kingdom
Order
Phylum
Domain
Genus
Species
Figure 4.22 Levels in a Linnaean taxonomic scheme-overview
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Classification and Identification of Microorganisms
• Linnaeus and Taxonomic Categories– Linnaeus proposed only two kingdoms
– Later taxonomic approach based on five kingdoms– Animalia, Plantae, Fungi, Protista, and
Prokaryotae
© 2012 Pearson Education Inc.
6/30/11 5MDufilho
Classification and Identification of Microorganisms
• Linnaeus and Taxonomic Categories– Linnaeus’s goal was to classify organisms to
catalogue them– Modern goal is to understand relationships
among groups of organisms– Reflect phylogenetic hierarchy – Emphasis on comparison of organisms’
genetic material – Led to proposal to add domain
© 2012 Pearson Education Inc.
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Classification and Identification of Microorganisms
• Domains– Carl Woese compared nucleotide sequences of
rRNA subunits
– Proposal of three domains as determined by ribosomal nucleotide sequences– Eukarya, Bacteria, and Archaea
– Cells in the three domains differ by other characteristics
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Classification and Identification of Microorganisms
• Taxonomic and Identifying Characteristics– Physical characteristics
– Biochemical tests
– Serological tests
– Phage typing
– Analysis of nucleic acids
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Gas bubble Inverted tubes to trap gas
Acid with gas Acid with no gas Inert
Hydrogensulfide
produced
No hydrogen
sulfide
Figure 4.23 Two biochemical tests for identifying bacteria-overview
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Negative result
Negative result
Positive result
Positive result
Figure 4.25 An agglutination test, one type of serological test-overview
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Figure 4.26 Phage typing
Bacterial lawn
Plaques
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Classification and Identification of Microorganisms
• Taxonomic Keys– Dichotomous keys
– Series of paired statements where only one of two “either/or” choices applies to any particular organism
– Key directs user to another pair of statements, or provides name of organism
© 2012 Pearson Education Inc.
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Figure 4.27 Use of a dichotomous taxonomic key-overview
Gram-positivecells?
Rod-shapedcells?
Gram-positivebacteria
Obligateanaerobes
Fermentslactose?
Cocci andpleomorphicbacteria
Cantolerateoxygen?
Can use citricacid (citrate)as sole carbonsource?
Non-lactose-fermenters
Produces gasfrom glucose?
Produces hydrogensulfide gas?
Produces acetoin? Salmonella
EnterobacterCitrobacter
EscherichiaShigella
YesNo
YesNo YesNo
YesNo
YesNo
YesNo
YesNo
YesNo
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