bacterial taxonomy classification and nomenclature

1. Presented by
Dr. Avinanda Biswas
Tutorof Microbiology
D Y Patil Medical College
and Hospital
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2. TAXONOMY
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Involves classification, nomenclature and identification
of organisms.
 classification is thearrangementof organisms intogroups
based on theirmutual similarity orevolutional relatedness.
 Nomenclature is the process of assigning names to a an
organism (and requiresagreement forunambiguous usageof
such names)
 Identification is thepractical process of determining thata
particular isolate belongs to a given recognized group.(
microbiologistsare usually concerned with this in practice)

3. Importance of Bacterial taxonomy
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⚫Helps in predictionsand frame hypotheses for further
research based on knowledgeof similarorganisms.
⚫Easycommunicationamong microbiologists
⚫Organization of knowledge.

4. Classification of Bacteria
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The most recent taxonomic classification of bacteria is
based on Cavailer and Smith’s six kingdom classification
at present (1998) . It is a molecular classification , which
devides all living structures of the earth into six
kingdoms– Bacteria , Protozoa , Chromista , Plantae ,
Fungi and Animalia .

5. Classification System
There is no universally accepted principle to classify
bacteria.There are mainly three approaches : Phylogenetic ,
Adansonian and molecular .
 Phylogenetic Classification :- There is a hierarchial
classification representing a branching tree-like
arrangements ; one characteristic (or trait) is being
employed for division at each node of the tree .
 This system is called phylogenetic because it implies an
evolutionary arrangement of species.
 This system is called phylogenetic because it implies an
evolutionary arrangement of species.

6. Systems contd….
The characteristics which are given importance depend upon
various properties of the organisms such as:
 Morphology of bacteria –cocci or bacilli
 Staining property such as lactose fermenting and non lactose fermenting
colonies .
 Biochemical reactions , e.g. coagulase positive Staphylococcus and coagualase
negative Staphylococcus.
 Antigenic structure ,e.g. antigenic structure of somatic antigen present in
bacterial cell wall .
Though ,this classification is a convenient and user friendly
method ,it is not a perfect method . Because the weighted
characters used may not be valid all the time for a given
bacterium . For example , fermentation of lactose though is
an important property to classify family Enterobacteriaceae ;
is not a permanent trait . In due course of time , bacteria may
lose or gain the property to ferment lactose .

7. Phylogenetic tree of classifying living
structure based weighted characterrs

8. Systems contd….
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Numerical (Adansonian) classification :- Some how
related to phenetic though information about the
properties of organisms is converted into numerical form
and compared using computer programms , similarity or
matching coefficients and dendograms are constructed .
(Robert Sokal and Peter H.A.Sneath)
Molecular Classification :- It is based on the degree of
genetic relatedness of different organisms . Guanine +
cytosine (G+C) content of bacteria is estimated after
extracting DNA from pure bacterial culture. The
nucleotide base composition and the base ratio vary widely
among different groups of microorganisms, but for any
one particular species ,it is constant.

9. Bacterial Nomenclature
Nomenclature is the branch of taxonomy ,that is
concerned with designating scientific names to
taxa , based on a particular classification scheme
and in accordance with agreed international rules
and conventions .
 Bacterial nomenclature also follows the same
rules as proposed by Carolus Linnaeus who
invented the modern system of binomial
nomenclature.
 Scientific names for taxonomic levels above
genus are always capitalized but not italicized ;
for example , Phylum Proteobacteria.
 In bionomical nomenclature system , the
scientific name of bacteria comprises of a genus
name (starts with capital letter) and species
name.Both genus and species should be written
in italic or are underlined ; e.g. Staphylococcus
aureus or Staphylococcus aureus .
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10. Contd..
 The genus (pleural : genera) is usually a Latin noun
whereas the species refers to a defined taxon of
organisms within a particular genus .
 The genus and species are coined based on some
property of the bacteria ; for example ,
 Staphylococcus aureus is named after their arrangement in cluster
(Staphyle means brunch of grapes) and type of pigmentation they
produce (aureus meaning in golden yellow) .
 Neisseria meningitidis is named after – the discover (U.Neisser) and
the disease it causes (meningitis) .
 Brucella suis and Brucella Melitensis (named after the discoverer
Brucella from David Bruce ) and the animal host (suis means pig) and
the place of discovery (melitensis from Malta, Europe) .

11. IDENTIFICATION OF MEDICALLY
IMPORTANT BACTERIA
Key parameters used:
⚫Cell wall (rigid, f lexible, orabsent).
⚫Intracellularorextracellular.
⚫Shapeof theorganism.
⚫Staining reaction.
⚫Spore forming abilities.
⚫Biochemical reactions.
⚫Genetics. (rRNA sequences, hybridization, gene probes)
⚫Cultural x-tics (diameter, outline, elevation,colour etc)
⚫Theability togrow in absence or presenceof oxygen
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