Question about these chapters

1. CHAPTER-2
CLASSIFICATION OF BACTERIA
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2. Learning Objectives
At the end of this chapter, the student should be able to:
 Describe Taxonomy of bacteria
 Discuss Phenotypic(morphological) characteristics
 Discuss Genotypic characteristics
 Describe bacterial Nomenclature
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3. Outline
• Taxonomy
• Phenotypic(morphological) characteristics
• Genotypic characteristics
• Nomenclature
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4. Introduction
Bacteriology
 The major sub-division of medical microbiology which study about
medically important bacteria.
Bacterial Cell
General property
 Typical prokaryotic cell
 Contain both DNA and RNA
 Most grow in artificial media
 Replication is by binary fission
 Contain rigid cell wall
 Sensitive to antimicrobial agent
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5. 2.1 Taxonomic Classification of Organisms
Taxonomy
 Science of systemic classification, identification and nomenclature of
organisms
 Provides universal names for organisms
 provides a reference for identifying organisms
 Provide information about evolution of organisms
 For classification purposes, organisms are usually organized into subspecies,
species, genera, families, and higher orders. 5

6. Cont…
Classification
 Is the orderly arrangement of bacteria into groups( taxa).
 Taxon:-a group or category of related organisms.
 Based on similarity or relationship.
 Different groups of scientists may classify the same organisms
differently.
The general criteria for classification (grouping) of microorganism are:
• Genotypic /evolutionary relationship)
• Phenotypic
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7. Hierarchy of classification
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8. Taxonomic rank
Domain
 The domain is a taxonomic category that, depending on point of view,
is either above the level of kingdom or supersedes the kingdom.
 The domain system contains three members.
• Eukaryotes ( domain Eukarya )
• Prokaryote ( domain Bacteria)
• Archaebacteria ( domain Archaea)
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9. Eukaryotic and prokaryotic cells
• Based on the cellular complexity or organization among unicellular
and Multicellular organisms by Electron microscope:
• Microorganisms can be classified as
1) Prokaryotic
 Bacteria
2) Eukaryotic
 Fungi
 Protozoa
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10. Cont…
A) Prokaryotic
 Pro primitive
 Karyon nucleus/ Nut shell
 Cells of lower life forms
 Having DNA which is not enclosed by membrane
 nuclear material is distributed in mass through the cytoplasm.
 Example: Bacteria
 They divide by binary fission.
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11. A typical prokaryotic cell.
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12. Cont…
B)Eukaryotic cells
 EU True/ real
 Karyon nucleus/ Nut shell
 More advanced, larger, contain membrane bounded organelles.
• Fungi
• Protozoa
• Cells of plants and animals
 They divide /multiply/ by a process called mitosis
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13. A typical eukaryotic animal cell
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14. Cont…
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15. Cont…
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16. Cont…
Kingdom
 Five kingdoms include
1. Plantae ( the plants)
2. Fungi ( the fungi)
3. Animalia ( the animals )
4. Protista ( the unicellular eukaryotes)
5. Monera ( the prokaryotes)
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17. Cont…
Species
 A bacterial species is defined by the similarities found among its
members.
 Properties used for defining a bacterial species:-
• Biochemical reactions
• Chemical composition
• Cellular structures
• Genetic characteristics
• Immunological features
 Are used in defining a bacterial species.
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18. Cont…
Strain
• Strain is the level below the species.
• 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
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• Strains that vary in morphology
Serovars
• Stains that vary in their antigenic properties

19. 2.2 Phenotypic classification
 Phenotypic characteristics are useful in classification and
Identification of bacteria
Classification of bacteria based on
 Morphologic Characteristics
• Microscopic (appearance, Staining reaction )
• Macroscopic (Cultural characteristics)
 Growth requirement
 Biochemical tests and etc
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20. Cont…
A) Morphology
It is appearance of bacteria when visualized under light microscope,
which includes
 Size
 Shape
 Arrangement
Size: -
 Bacteria have different size.
 Most bacteria range from 0.2 - 5 μm in length and 0.2 - 1.5 μm in
diameter.
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21. Categories of bacteria based on the shape of
their cells
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22. Morphology...........
 Shape and arrangement
1) Cocci
• Round or oval bacteria
• Measuring about 0.5-1.0 μm in diameter.
 Arrangement
Monococcus: - single
Diplococcus: - arranged in pair
Streptococcus: - chain forming
Staphylococcus: -Cocci in
irregular groups ( in cluster)
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23. Morphologic arrangements of cocci and examples
of bacteria having these arrangements.
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24. Morphology.....
2) Bacilli (Rod)
 Stick- like bacteria
 Measuring 1-10 μm in length by 0.3 - 1.0 μm in width.
Arrangement
• Singly e.g. S. typhi
• Form chains, e.g. Streptobacillus species
• Form branching chains, e.g. Lactobacillus
• Mass together, e.g. Mycobacterium leprae
• Forming angle (Chinese letter) e.g. Corynebacterium diphtheria
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25. Morphology.....
i) Cocco bacillus
 They are short bacilli.
 Their size is smaller than bacillus and bigger than coccus
 E.g., Haemophilus influenza
Bordetella pertussis
Brucella abortus
ii) Comma shaped
 They assume rod shape and are curved like comma.
 E.g., Vibrio cholera
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26. Morphology.......
3) Spiral shaped bacteria
 It is a twisted ,flexible, coiled, motile organisms.
a) Treponemas
 Thin delicate with regular tight coils.
 6 –15 μm by 0.2 μm in width.
 E.g. Treponema pallidum
b) Borreliae
 Large spirochetes with irregular open coils.
 10–20 μm in length by about 0.5μm in width.
 E.g. Borrelia recurrentis
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27. Morphology.......
c) Leptospira
 Thin spirochaetes with many tightly
packed coils that are difficult to distinguish.
 6–20μm in length by 0.1μm in width and
have hooked ends.
 Leptospira interrogans
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28. Classification.....
B)Staining
 Is the process of coloring of colorless object using stains (dyes).
Type of staining methods
1. Simple staining method
 Identify shape and arrangement of bacteria
2. Differential staining method
 Gram staining
• Gram positive and Gram negative bacteria
 Ziehl-Neelsen (acid fast staining technique)
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• Acid Fast Bacilli (AFB)
3. Special staining method

29. Examples
Gram positive
 Staphylococcus
 Streptococcus
 Clostridium
 Bacillus
 Corynebacterium and etc
Gram negatives
 Neisseria spp.
 Haemophilus spp.
 Vibrio
 Salmonella
 Shigella spp
 Proteus
 Klebsiella
 Brucella
 Yersinia
 Coliforms and etc
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30. Examples
Acid fast bacilli (AFB)
 Mycobacterium tuberculosis
 Mycobacterium leprae
 Mycobacterium bovis (Cattle )
 Mycobacterium africanum
 Mycobacterium ulcerance
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31. C) Based on growth requirement
1) Oxygen requirement
Obligatory (strict) aerobes
 Need free oxygen for their growth.
 E.g. Pseudomonas aeruginosa, M. tuberculosis
Facultative anaerobes
 Can grow either in the presence or absence of O2.
 E.g. S. aureus, E. coli, salmonella, Shigella, Vibrio, Haemophilus,
Proteus
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32. Growth requirement…..
Obligate or strict anaerobes: -
 Only grow in absence of free oxygen.
 E.g. Clostridium perfringens, Bacteroides fragilis C. tetani,, etc….
Microaerophilic
 Need small amount of oxygen for growth.
 E.g. Campylobacter species.
Carboxyphilic:
 Bacteria require an atmosphere which contains CO2.
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33. 2) PH requirement
Most bacteria grow or reproduce at a pH range of 6 - 8
Classification of bacteria based on PH
a) Neutrophilic
 Bacteria which grow at a pH between 6-8.
b) Acidophilic
 Bacteria which can grow at a pH less than 7.0.
 E.g. Lactobacillus
c) Alkalophilic
 Few bacteria grow at a pH higher than 8.0.
 E.g. Vibrio cholera
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34. 3) Temperature
 Wide range of temperature
 This range can influence enzymatic activity.
i) Psychrophilic
 Bacteria which can grow at a temperature B/n -5 to 200C (cause spoilages of
food at 2-80C).
ii) Mesophilic
 Grow at a temperature between 20-450C (pathogenic)
iii) Thermophilic
 Prefer high temperature (50-800C) (cause spoilage of under processed canned
food)
Note:-
 Most pathogenic bacteria are mesophilic.
 Spore form bacteria can survive in any of the above temperature conditions. 34

35. 4) Moisture
 Most bacteria need optimum amount of moisture.
 Some bacteria needs high amount of moisture. Example
T. palladium
N. gonorrhea
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36. 5) Nutritional requirement
 Bacteria need nutrition for synthesis of protoplasm and energy.
Simple: - All bacteria need source of
1) Carbon 3)Energy
2) Nitrogen 4) Water and 5) mineral salts
Complex
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 Some bacteria need growth factors (vitamins).
 Fastidious bacteria.
 E.g. Neisseria gonorrhea, Haemophilus influenza etc..
Halophilic
 Those bacteria which live (grow) on high salt concentration.
 E.g. Staphylococcus aureus

37. D)Biochemical reaction
 Biochemical reaction can be used for classifying bacteria in to different groups.
i) Enzymes
 Coagulase positive. Eg S. aureus
 Catalase positive. Eg Staphylococci species
 Urease. Eg Proteus species
ii) Metabolic end product
 Gas producer
 Acid, or H2S from carbohydrates.
iii) Carbohydrate utilization
 Lactose fermenter
 Glucose fermenter
 Sucrose fermenter 37

38. 2.3 Genotypic Classification
Phylogenetic Approach :-
The ideal means of identifying and classifying bacteria would be to
compare each gene sequence in a given strain with the gene sequences
for every known species.
 This method can be used to measure the number of DNA sequences
that any two organisms have in common and to estimate the
percentage of divergence within DNA sequences that are related but
not identical
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39. Phylogenetic Approach….
 Five factors can be used to determine DNA relatedness:
1) genome size
2) guanine-plus-cytosine (G+C) content
3) DNA relatedness under conditions optimal for DNA reassociation
4) Thermal stability of related DNA sequences, and
5) DNA relatedness under conditions supraoptimal for DNA
reassociation.
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40. Phylogenetic Approach…..
1. Genome size
 Genome size determinations sometimes can distinguish between groups.
2. Guanine plus cytosine (G+C) content
 The G+C content in bacterial DNA ranges from about 25-75%
 This percentage is specific, but not exclusive, for a species
 Two strains with a similar G+C content may or may not belong to the same
species.
 If the G+C contents are very different, however, the strains cannot be members
of the same species.
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41. Phylogenetic Approach…..
3. DNA relatedness under conditions optimal for DNA re-
association
 DNA relatedness is determined by allowing single-stranded DNA from
one strain to re-associate with single-stranded DNA from a second
strain and to form a double-stranded DNA molecule
 Many studies indicate that a bacterial species is composed of strains
that are 70 to 100 percent related.
 The term "related" does not mean "identical" or "homologous.”
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42. Phylogenetic Approach…..
4. Thermal stability of related DNA sequences
 Each 1% of unpaired nucleotide bases in a double-stranded DNA
sequence causes a 1% decrease in the thermal stability
 A comparison between the thermal stability of a control double-
stranded molecule (in which both strands of DNA are from the same
organism) and that of a heteroduplex (DNA strands from two different
organisms) allows assessment of divergence between related
nucleotide sequences.
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43. Phylogenetic Approach…..
5. DNA Relatedness under Supra-optimal Conditions for DNA
Reassociation
 When the incubation temperature used for DNA re-association is
raised from 25-30° C below the denaturation temperature to only 10-
15° C below the denaturation temperature, only very closely related
DNA sequences can re-associate.
 Strains from the same species are 60% or more related at these supra-
optimal incubation temperatures.
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44. Cont…
 DNA relatedness provides one species definition that can be applied
equally to all organisms.
 It cannot be affected by phenotypic variation, mutations, or the
presence or absence of metabolic or other plasmids.
 It measures overall relatedness, and these factors affect only a very
small percentage of the total DNA.
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45. Numerical Approach to taxonomy
 In numerical taxonomy (also called computer or phenetic taxonomy)
 Many (50 to 200) biochemical, morphological, cultural characteristics,
susceptibilities to antibiotics and inorganic compounds, are used to determine
the degree of similarity between organisms
 In numerical studies, investigators often calculate the coefficient of similarity
or percentage of similarity between strains.
 A dendrogram or a similarity matrix is constructed that joins individual
strains into groups and places one group with other groups on the basis of their
percentage of similarity.
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46. Example of dendogram
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47. Polyphasic approach to taxonomy
 In practice, the approach to bacterial taxonomy should be polyphasic.
 The first step is phenotypic grouping of strains by morphological,
biochemical and any other characteristics of interest.
 The phenotypic groups are then tested for DNA relatedness to
determine whether the observed phenotypic homogeneity (or
heterogeneity) is reflected by phylogenetic homogeneity or
heterogeneity.
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48. Cont…
 The third and most important step is reexamination of the biochemical
characteristics of the DNA relatedness groups.
 This allows determination of the biochemical borders of each group
and determination of reactions of diagnostic value for the group
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49. Bacterial identification; a polyphasic approach.
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50. 2.4 Nomenclature(Naming)
 Is the means by which the characteristics of a species are defined and
communicated.
 There are two kinds of naming of microorganisms
i) Scientific or International naming
• The same throughout the world
• It is binomial nomenclature system employs the name of the two
level taxa (genes and species).
• Example Bacillus subtlis, Escherchia coli, Salmonella typhi etc.
ii) Causal or common naming
• This type of naming is varies from country to country
• Example typhoid bacilli and gonococcus
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51. I) Scientific name (systematic name)
 Also called binomial system of nomenclature
 Genus name + species name
 Genus name comes before species name
 Carolus Linnaeus (1735) established the system of scientific
nomenclature.
 Each organism has two names: the genus and species, and this
scientific name is common universally.
 Exception:- example
 Clostridium perfringens in the USA
 Clostridium welchii in England
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52.  Species are named according to principles and rules of nomenclature
set forth in the Bacteriological Code
Genus name always capitalized while species is not and both should
be underlined or italicized
• E.g. Staphylococcus aureus or Staphylococcus aureus
Genus name 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
• The first and the second name together referred as species
• Shigella dysenteriae or
• S. dysenteriae or
• Shigella dysenteriae
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53. Nomenclature.....
ii) Common or descriptive names
Names for organisms that may be in common usage, but are not
taxonomic names.
Example:-
 Tubercle bacillus…(Mycobacterium tuberculosis)
 Meningococcus …(Neisseria meningitidis)
 Group A Streptococcus….(Streptococcus pyogenes)
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54. Nomenclature.....
 Sometimes, bacteria and other microorganisms are named
for the person who discovered the organism.
• Bordetella (Jules Bordet)
• Escherichia (Theodore Escherich)
• Neisseria (Albert Ludwig Neisser)
• Salmonella (Daniel Elmer Salmon)
Bacterial characteristics ( shape, motility…)
For Place
For Pathological change
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55. References
 Levinson W., Jawetz E., Medical Microbiology and Immunology. 6th
ed. McGraw- Hill international edition. 2000.
 Brooks G.F., Butel J.S., Morse S.A Jawetz Medical Microbiology 21st
ed. (1998).
 Murray, Medical microbiology
 Robert Boyd. Basic Medical Microbiology. 5th ed. (1995)
 Monica Cheesbrough. District Laboratory Practice in Tropical
Countries. Volume-2 (2000)
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56. THE END OF CHAPTER-2
THANK YOU!!!
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