chapter 4.0 microscopy, staining, and classification · 2020-06-18 · chapter 4.0 microscopy,...
TRANSCRIPT
Chapter 4.0 Microscopy, Staining, and
Classification
MDufilho 8/20/2017 1
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
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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
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Figure 4.19 Levels in a taxonomic scheme.
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Bacteria Archaea Eukarya
Fungi Plantae Animalia
Chordata
(vertebrates)
Arthropoda
(joint-legged animals)
Platyhelminthes
(tapeworms)
Nematoda
(unsegmented roundworms)
Arachnida Crustacea Insecta
Scorpionida Acariformes
(mites)
Parasitiformes
(mites and ticks)
Araneida
Argasidae
(soft ticks)
Ixodidae
(hard ticks)
Dermacentor Ixodes Rhipicephalus
I. scapularis
(deer tick)
I. pacificus
(black-eyed tick)
I. ricinus
(castor bean tick) 8/20/2017 MDufilho 4
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
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
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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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Figure 4.20 Two biochemical tests for identifying bacteria.
No
hydrogen
sulfide
Hydrogen
sulfide
produced Acid with gas Acid with no gas Inert
Gas bubble Inverted tubes to trap gas
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Figure 4.22 An agglutination test, one type of serological test.
Negative result Positive result
Negative result Positive result
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Figure 4.23 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
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Figure 4.24 Use of a dichotomous taxonomic key.
1a. Gram-positive cells………………………… Gram-positive bacteria 1b. Gram-negative cells………………………... 2
2a. 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
Gram-positive
cells?
Rod-shaped
cells?
Gram-positive
bacteria
Cocci and
pleomorphic
bacteria
Can
tolerate
oxygen?
Obligate
anaerobes
Ferments
lactose?
Non-lactose-
fermenters
Can use citric
acid (citrate)
as sole carbon
source?
Produces gas
from glucose?
Produces hydrogen
sulfide gas?
Shigella Escherichia Produces
acetoin? Salmonella
Citrobacter Enterobacter
No Yes No Yes
Yes No
No Yes
No Yes
No Yes
No Yes
Yes No
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Dichotomous Keys: Overview
Dichotomous Keys: Overview
PLAY
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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