Chapter 4.0 Microscopy, Staining, and Classification

Transcription

1 Chapter 4.0 Microscopy, Staining, and Classification 8/20/2017 MDufilho 1

2 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 To understand evolutionary connections 8/20/2017 MDufilho 2

3 Classification and Identification of Microorganisms Linnaeus and Taxonomic Categories Linnaeus His system classified organisms based on common characteristics Grouped organisms that can successfully interbreed into categories called species Used binomial nomenclature 8/20/2017 MDufilho 3

4 Figure 4.19 Levels in a taxonomic scheme. Domain Bacteria Archaea Eukarya Kingdom Animalia Plantae Fungi Phylum Chordata (vertebrates) Arthropoda (joint-legged animals) Platyhelminthes (tapeworms) Nematoda (unsegmented roundworms) Class Insecta Crustacea Arachnida Order Scorpionida Acariformes (mites) Parasitiformes (mites and ticks) Araneida Family Ixodidae (hard ticks) Argasidae (soft ticks) Genus Dermacentor Ixodes Rhipicephalus Species 8/20/2017 MDufilho 4 I. scapularis (deer tick) I. pacificus (black-eyed tick) I. ricinus (castor bean tick)

5 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 Linnaeus's goal was classifying organisms to catalog them Modern goal is understanding relationships among organisms Goal of modern taxonomy is to reflect phylogenetic hierarchy Greater emphasis on comparisons of organisms' genetic material led to proposal to add domain 8/20/2017 MDufilho 5

6 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 also differ with respect to many other characteristics 8/20/2017 MDufilho 6

7 Classification and Identification of Microorganisms Taxonomic and Identifying Characteristics Physical characteristics Biochemical tests Serological tests Phage typing Analysis of nucleic acids 8/20/2017 MDufilho 7

8 Figure 4.20 Two biochemical tests for identifying bacteria. Gas bubble Inverted tubes to trap gas Acid with gas Acid with no gas Inert Hydrogen sulfide produced No hydrogen sulfide 8/20/2017 MDufilho 8

9 Figure 4.22 An agglutination test, one type of serological test. Negative result Positive result Negative result Positive result 8/20/2017 MDufilho 9

10 Figure 4.23 Phage typing. Bacterial lawn Plaques 8/20/2017 MDufilho 10

11 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 8/20/2017 MDufilho 11

12 Figure 4.24 Use of a dichotomous taxonomic key. 1a. Gram-positive cells Gram-positive bacteria 1b. Gram-negative cells a. Rod-shaped cells 3 2b. Non-rod-shaped cells Cocci and pleomorphic bacteria 3a. Can tolerate oxygen 4 3b. Cannot tolerate oxygen. Obligate anaerobes 4a. Ferments lactose 5 4b. Cannot ferment lactose Non-lactose-fermenters 5a. Can use citric acid as a sole carbon source...6 5b. Cannot use citric acid alone...8 6a. Produces hydrogen sulfide gas.. Salmonella 6b. Does not produce hydrogen sulfide gas 7 7a. Produces acetoin. Enterobacter 7b. Does not produce acetoin. Citrobacter 8a. Produces gas from glucose.. Escherichia 8b. Does not produce gas from glucose.. Shigella No Cocci and pleomorphic bacteria Rod-shaped cells? No Obligate anaerobes Gram-positive cells? No Yes Can tolerate oxygen? Non-lactosefermenters Shigella No Yes Gram-positive bacteria Yes Ferments lactose? Produces gas from glucose? Can use citric acid (citrate) as sole carbon source? No Yes Escherichia Yes Produces hydrogen sulfide gas? No Yes No Yes No Citrobacter Produces acetoin? Yes Enterobacter Salmonella 8/20/2017 MDufilho 12

13 Dichotomous Keys: Overview PLAY Dichotomous Keys: Overview 8/20/2017 MDufilho 13

14 Micro Matters In the Micro Matters video in chapter 4, Cindy researches how penicillin works to treat her strep throat infection. The bacterium Streptococcus pyogenes causes strep throat. Bacteria are often classified as Gram-positive or Gram-negative based on their cell wall structure. The outer membrane of Gram-negative bacteria is not permeable to large molecules such as the antibiotic penicillin. Penicillin inhibits the proper formation of peptidoglycan which can make bacterial cells susceptible to osmotic pressure. 8/20/2017 MDufilho 14