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بسم ال الرحمن الرحيم
Prof. Khalifa Sifaw Ghenghesh
Dept. of Medical Microbiology,
, Faculty of Medicine
Tripoli - Libya
(Carolus Linnaeus (1707–1778
– Swedish botanist credited with founding the science
– 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.
• The science of classification and refers to
– Nomenclature and
A Comparison of the More Notable
Classification Systems of Living Organisms
Haeckel (1894( Whittaker (1959(
Three kingdoms Five kingdoms
The Phylogenetic Tree of Life based on
Comparative ssrRNA* Sequencing.
*the nucleotide sequences of the small subunit ribosomal RNA.
• The systematic division of organisms
into related taxa (groups) based on
1. Conventional Classification
Major characteristics used in conventional classification:
Mechanism of motility
Carbon & nitrogen
Cell wall constituents
optimum & range
pH optimum & growth
Sensitivity to metabolic
inhibitors & antibiotics
Adansonian or Numerical. 2
• Numerical taxonomy, the use of
• A large number of biochemical,
morphological and cultural characteristics are used to determine the
degree of similarity between organisms
(similarity matris) and conversion to
Phylogenetic Classification. 3
• 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
• PURE CULTURE:
Populations of individuals all derived
from the same single organism.
A Group of Pure Cultures Derived from a
Common Source and Thought to be the
A Group of Closely Similar Strains.
• Naming of microorganisms.
• Governed by international rules
• Rules published in the International
Code of Nomenclature of Bacteria.
• The International Journal of Systematic
Rules for the Nomenclature of
• There is only one correct name for an organism.
• Names that cause error or confusion should be
• All names in Latin or are latinized.
– The first word (genus) is always capitalized.
– The second word (species or specific epithet) is not
– Both genus and species name, together referred to as
species, are either underlined or italicized when appearing
– 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.
• Casual or Common Name:
• e.g. "typhoid bacillus"
• Scientific or International Name:
• Biologists often use a taxonomic key to
identify organisms according to their
• Dichotomous key
– most commonly used in identification.
– has paired statements describing
characteristics of organisms.
Methods used for Identification of
Analysis of metabolic end products or structural
components of organisms by different methods (e.g.
• Genetic analysis using nucleic acid probes and
other molecular techniques (e.g. PCR)
• Dichotomous Key
– Methods for distinguishing and identifying
bacteria are assembled into Bergey's
Manual of Determinative Bacteriology
– Bergey's Manual of Systematic
Provides description of physical & chemical
characteristics and system of identification of
medically important members of selected
sections of bacteria
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
– 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.