Carolus Linnaeus established the scientific system of taxonomy in the 18th century, introducing binomial nomenclature and a hierarchical ranking system of taxa from species to kingdom. Over time, new classification systems were proposed based on emerging data from cell morphology, biochemistry, genetics, and molecular analysis. Modern bacterial taxonomy utilizes a polyphasic approach, integrating multiple lines of evidence from phenotypic and genotypic characterization to phylogenetically group and identify bacterial organisms.

1. BACTERIAL TAXONOMY

2. Carolus Linnaeus (1707–1778)
– Swedish botanist credited with founding the science
of taxonomy.
– He introduced the binomial system of nomenclature
– Linnaeus also established a hierarchy of taxonomic
ranks: species, genus, family, order, class, phylum
or division, and kingdom.
– At the highest level, Linnaeus divided all living
things into two kingdoms—plant and animal.
– In his taxonomic hierarchy each organism is
assigned a species name, and species of very
similar organisms are grouped into a
genus and so on.

3. Taxonomy
• The science of classification and refers to
– Classification
– Nomenclature and
– Identification

4. A Comparison of the More Notable
Classification Systems of Living Organisms
Haeckel (1894) Whittaker (1959) Woese (1977) Woese (1990)
Three kingdoms Five kingdoms Six kingdoms Three domains
---------------------------------------------------------------------------------------------------------
Protista Monera Eubacteria Bacteria
Plantae Protista Archaebacteria Archaea
Animalia Fungi Protista Eukarya
Plantae Fungi
Animalia Plantae
• Animalia

5. The Phylogenetic Tree of Life based on
Comparative ssrRNA* Sequencing.
*the nucleotide sequences of the small subunit ribosomal RNA.

7. Classification

8. • The systematic division of organisms
into related taxa (groups) based on
similar characteristics

9. 1. Conventional Classification
Major characteristics used in conventional classification:
• Cell shape
• Cell size
• Colonial morphology
• Ultrastructural
characteristics
• Staining behaviour
• Mechanism of motility
• Cellular inclusions
• Carbon & nitrogen
sources
• Cell wall constituents
• Energy sources
• Fermentation products
• Growth temperature
optimum & range
• Osmotic tolerance
• Oxygen relationships
• pH optimum & growth
range
• Sensitivity to metabolic
inhibitors & antibiotics
Feature:

10. 2. Adansonian or Numerical
Classification
• Numerical taxonomy, the use of
computers.
• A large number of biochemical,
morphological and cultural chara-
cteristics are used to determine the
degree of similarity between organisms
(similarity matris) and conversion to
dendogram (phenogram)

11. OTU = operational taxonomic unit

12. 3. Phylogenetic Classification
• An evolutionary arrangement of species.
• Sharing a recent ancestor as in plants and
animals (fossil records)
• In bacteria?
• Possible by Molecular Methods
– Genetic Homology:
• Base composition (GC ratio)
• Nucleic acid hybridisation.
• Ribosomal RNA (rRNA) sequence analysis
• Protein profiles and amino acid sequences

13. • PURE CULTURE:
• Populations of individuals all derived
from the same single organism.
• STRAIN:
• A Group of Pure Cultures Derived from a
Common Source and Thought to be the
Same.
• SPECIES:
• A Group of Closely Similar Strains.

14. INTRASPECIES CLASSIFICATION
• Biotypes
– Biochemical properties.
• Serotypes
– Antigenic features.
• Phage Types
– Bacteriophage susceptibility.
• Colicin Types
– Production of bacteriocins.

15. Nomenclature

16. • Naming of microorganisms.
• Governed by international rules
• Rules published in the International
Code of Nomenclature of Bacteria.
• The International Journal of Systematic
Bacteriology

17. Rules for the Nomenclature of
Microorganisms
• There is only one correct name for an organism.
• Names that cause error or confusion should be
rejected.
• All names in Latin or are latinized.
– The first word (genus) is always capitalized.
– The second word (species or specific epithet) is not
capitalized.
– Both genus and species name, together referred to as
species, are either underlined or italicized when appearing
in print.
– The correct name of a species or higher taxonomic
designations is determined by valid publication, legitimacy
of the name with regard to the rules of nomenclature, and
priority of publication.

18. Nomenclature
• Casual or Common Name:
• e.g. "typhoid bacillus"
• Scientific or International Name:
• Salmonella typhi
• Salmonella london
• Staphylococcus aureus
• Clostridium tetani
• Mycobacterium bovis
• Borrelia burgdorferi

19. Identification

20. • Biologists often use a taxonomic key to
identify organisms according to their
characteristics.
• Dichotomous key
– most commonly used in identification.
– has paired statements describing
characteristics of organisms.

21. Methods used for Identification of
Bacteria
• Cellular morphology
• Staining characteristics
• Motility
• Growth characteristics
• Biochemical characteristics
• Serological tests
• Analysis of metabolic end products or structural
components of organisms by different methods (e.g.
GLC)
• Genetic analysis using nucleic acid probes and other
molecular techniques (e.g. PCR)

22. TEST
Organism Gram Shape Catalase Indole
B. subtilis + Rod + -
C. freundii - Rod + -
E. faecium + Coccus - -
P. vulgaris - Rod + +
S. aureus + Coccus + -

23. • Dichotomous Key
Gram reaction
+ -
indole
+ -
morphology
rods cocci
B. subtilis
catalase
+ -
S. aureus E. faecium
P. vulgaris C. freundii

24. Enterotube

25. • Bergey's Manual
– Methods for distinguishing and identifying
bacteria are assembled into Bergey's
Manual of Determinative Bacteriology
– Bergey's Manual of Systematic
Bacteriology
• Provides description of physical & chemical
characteristics and system of identification of
medically important members of selected
sections of bacteria

26. Polyphasic Bacterial Taxonomy
• More data will become available, more bacteria will be
identified, there will be more information, and software
development will need to address the combination and
linking of the different databases.
• A polyphasic approach to bacterial classification
includes:
– Methods to phylogenetically allocate bacteria
– Methods to compare and group large numbers of strains into
clusters of similar bacteria
– DNA-DNA hybridization to determine the relationships between
represnetativies withing and between each of those clusters
– And descriptive methods which will provide further genotypic
and phenotypic information.