Chapter 4 Microscopy, Staining, and Classification 6/30/11MDufilho

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 6/30/112MDufilho

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. 6/30/113MDufilho

l. scapularis (deer tick) l. pacificus (black-eyed tick) l. ricinus (castor bean tick) Parasitiformes (mites and ticks) Acariformes (mites) Rhipicephalus Ixodidae (hard ticks) DermacentorIxodes Argasidae (soft ticks) Araneida Scorpionida Arachnida CrustaceaInsecta Chordata (vertebrates) Arthropoda (joint-legged animals) Platyhelminthes (tapeworm) Nematoda (unsegmented roundworms) Animalia PlantaeFungi BacteriaArchaeaEukarya Family Class Kingdom Order Phylum Domain Genus Species Figure 4.22 Levels in a Linnaean taxonomic scheme-overview 6/30/114MDufilho

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. 6/30/115MDufilho

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. 6/30/116MDufilho

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 © 2012 Pearson Education Inc. 6/30/117MDufilho

Classification and Identification of Microorganisms Taxonomic and Identifying Characteristics –Physical characteristics –Biochemical tests –Serological tests –Phage typing –Analysis of nucleic acids © 2012 Pearson Education Inc. 6/30/118MDufilho

Gas bubble Inverted tubes to trap gas Acid with gas Acid with no gasInert Hydrogen sulfide produced No hydrogen sulfide Figure 4.23 Two biochemical tests for identifying bacteria-overview 6/30/119MDufilho

Negative result Positive result Figure 4.25 An agglutination test, one type of serological test-overview 6/30/1110MDufilho

Figure 4.26 Phage typing Bacterial lawn Plaques 6/30/1111MDufilho

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. 6/30/1112MDufilho

Figure 4.27 Use of a dichotomous taxonomic key-overview Gram-positive cells? Rod-shaped cells? Gram-positive bacteria Obligate anaerobes Ferments lactose? Cocci and pleomorphic bacteria Can tolerate oxygen? Can use citric acid (citrate) as sole carbon source? Non-lactose- fermenters Produces gas from glucose? Produces hydrogen sulfide gas? Produces acetoin? Salmonella Enterobacter Citrobacter Escherichia Shigella Yes No Yes No Yes No Yes No Yes No Yes No Yes No Yes No 6/30/1113MDufilho