Lecture 3: Principles and methods of microbial classification - PowerPoint PPT Presentation

Loading...

PPT – Lecture 3: Principles and methods of microbial classification PowerPoint presentation | free to view - id: 1167d0-YTBjN



Loading


The Adobe Flash plugin is needed to view this content

Get the plugin now

View by Category
About This Presentation
Title:

Lecture 3: Principles and methods of microbial classification

Description:

Phenetic Classification System: ... bacteria into phenetic groups, used in ... Bacteriology was published, still primarily phenetic in its classification. ... – PowerPoint PPT presentation

Number of Views:3641
Avg rating:3.0/5.0
Slides: 21
Provided by: JUs17
Category:

less

Write a Comment
User Comments (0)
Transcript and Presenter's Notes

Title: Lecture 3: Principles and methods of microbial classification


1
Lecture 3 Principles and methods of microbial
classification
  • Learning outcomes
  • Students should be able to
  • Understand the basic principles of microbial
    classification systems.
  • Be familiar with structural and biological
    characteristics to classify bacteria
  • List the genetic approaches that can be used in
    identification and classification of bacteria

2
Microbial Identification
  • Basic Concepts of Identification
  • Isolation and Identification of Specimens
  • Reading material
  • Jawetz, Melnick Adelbergs, Medical
    Microbiology, Chapter 3.
  • Prescott, Harley, Klein. Microbiology. Chapter
    2.

3
Basic Principles
  • Classification Systems
  • Levels of Classification
  • Definition of Species
  • Nomenclature
  • Useful Properties in Microbial Classification
  • Microbial Phylogeny

4
Classification Systems
  • Taxonomy
  • Classification of living organisms into groups
  • Phylogenetic Classification System
  • Groups reflect genetic similarity and
    evolutionary relatedness
  • Phenetic Classification System
  • Groups do not necessarily reflect genetic
    similarity or evolutionary relatedness. Instead,
    groups are based on convenient, observable
    characteristics.

5
Phylogenetic tree classification by molecular
and cellular relationships
6
Levels of Classification
  • Taxon
  • A group or level of classification
  • Hierarchical broad divisions are divided up into
    smaller divisions
  • Kingdom (Not used by most bacteriologists)
  • Phylum (Called Division by botanists)
  • Class
  • Order
  • Family
  • Genus (plural Genera)
  • Species (Both singular plural)

7
Definition of Species
  • The basic unit of taxonomy, representing a
    specific, recognized type of organism
  • For sexually reproducing organisms, a fundamental
    definition of species has been reproductive
    compatibility
  • This definition fails for many microbial species
    (including bacteria), because they do not
    reproduce sexually

8
Definition of Species
  • Defintion of species in microbiology
  • Classic definition A collection of microbial
    strains that share many properties and differ
    significantly from other groups of strains
  • Species are identified by comparison with known
    type strains well-characterized pure cultures
    references for the identification of unknowns
  • There are several collections of type strains,
    including the American Type Culture Collection
    (ATCC)

9
Definition of Species
  • Defintion of species in microbiology (cont.)
  • Strain
  • A population of microbes descended from a single
    individual or pure culture
  • Different strains represent genetic variability
    within a species
  • Biovars Strains that differ in biochemical or
    physiological differences
  • Morphovars Strains that vary in morphology
  • Serovars Stains that vary in their antigenic
    properties

10
Nomenclature
  • Scientific name (Systematic Name) Binomial
    System of Nomenclature
  • Genus name species name
  • Italicized or underlined
  • Genus name is capitalized and may be abbreviated
  • Species name is never abbreviated
  • A genus name may be used alone to indicate a
    genus group a species name is never used alone
  • eg Bacillus subtilis       B. subtilis

11
Nomenclature
  • Common or descriptive names (trivial names)
  • Names for organisms that may be in common usage,
    but are not taxonomic names
  • eg tubercle bacillus         (Mycobacterium
    tuberculosis)
  • meningococcus (Neiserria meningitidis)
  • Group A streptococcus (Streptococcus pyogenes)

12
Useful Properties in Classification
  • Colony morphology
  • Cell shape arrangement
  • Cell wall structure (Gram staining)
  • Special cellular structures
  • Biochemical characteristics

13
Useful Properties in Classification
  • Serological Tests
  • Use group specific antiserum isolated from the
    plasma of animals that have been sensitized to
    the organism
  • The antiserum contains antibody proteins that
    react with antigens on the unknown organism.
  • The reaction can be detected by examining
    agluttination or by using sera labeled with
    colorimetric or fluorescent labels

14
Useful Properties in Classification
  • Serological Tests (cont.)
  • Advantages
  • Highly specific
  • Does not usually require the organism to be
    isolated into pure culture
  • Can be used to identify organisms that cant be
    grown on medium

15
Useful Properties in Classification
  • G C content
  • Estimated by determining the melting temperature
    of the DNA
  • Higher G C gives a higher melting temperature

16
Useful Properties in Classification
  • Nucleic acid hybridization
  • By mixing ssDNA from two different species and
    determining the percentage of the DNA that can
    form dsDNA hybrids
  • The greater the percent hybridization, the closer
    the species

17
Useful Properties in Classification
  • Nucleic acid sequencing
  • Genes for specific enzymes
  • The nucleic acid sequence for the complete genome
    of several species is now available
  • 5S and 16S rRNA (ribosomal RNA) sequences
    comparison of these sequences has been
    extensively used to determine the phylogenetic
    relationships of microbial groups

18
Microbial Phylogeny
  • Bergeys Manual of Systematic Bacteriology
  • In 1927, David Bergey colleagues published
    Bergeys Manual of Determinative Bacteriology, a
    manual that grouped bacteria into phenetic
    groups, used in identification of unknowns. It is
    now in its 9th edition.
  • In 1984, a more detailed work entitled Bergeys
    Manual of Systematic Bacteriology was published,
    still primarily phenetic in its classification.

19
Microbial Phylogeny
  • Bergeys Manual of Systematic Bacteriology
  • Publication of the second edition of Bergeys
    Manual of Systematic Bacteriology was begun in
    2001.
  • The 2nd edition gives the most up-to-date
    phylogenic classification of prokaryotic
    organisms, including both eubacteria and archaea.
  • When it is completed, it will consist of 5
    volumes.
  • The classification in Bergeys Manual is accepted
    by most microbiologists as the best concensus for
    prokaryotic taxonomy.

20
Isolation and Identification
  • Basic concepts of isolation, dichotomous keys,
    and molecular methods in identification
  • Prescotts Microbiology, Chapter 36, pp 804 818
  • Numerical Taxonomy
  • Prescotts Microbiology pp 414 420
About PowerShow.com