BY MWEBAZA IVANMsci I

2013/HD07/767U

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TAXONOMY

Involves classification, nomenclature and identification of organisms.

classification is the arrangement of organisms into groups based on their mutual similarity or evolutional relatedness.

Nomenclature is the process of assigning names to a an organism (and requires agreement for unambiguous usage of such names)

Identification is the practical process of determining that a particular isolate belongs to a given recognized group.( microbiologists are usually concerned with this in practice)

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DOMAINS OF LIFE

All life forms belong to three large groups/domains i.e. Archaea, bacteria and eukarya (three domain system-carl woese, 1977).

Eukarya-

Have membrane bound organelles.

DNA is linear and found on x-somes in nucleus.

Transcription requires formation of mRNA and moves outside of the nucleus.

Have glycerol fatty acyl diester membrane lipids.

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ARCHAEA classified as separate from Bacteria by Carl woese in

1977 basing on rRNA gene sequences,

considered as prokaryotes along side Bacteria.

Their transcription and translation enzymes are more similar to those of eukaryotes than of bacteria.

Have isoprenoid glycerol diether or diglycerol tetraether lipids.

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BACTERIAHave no membrane bound organelles,

Have single circular DNA.

Transcription and translation can be carried out simultaneously.

Have diacyl glycerol diester lipids in their membranes.

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Importance of Bacterial taxonomy

Helps in predictions and frame hypotheses for further research based on knowledge of similar organisms.

Easy communication among microbiologists

Organization of knowledge.

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Classification of BacteriaBacteria are arranged into species, genera, families, orders

and phyla. The species is the basic group.A prokaryotic species is a collection of strains which share

many stable properties and differ significantly from other groups.

It should have similar G+C composition and 70% or greater similarity as judged by DNA hybridization.

Species should ideally be distinguishable phenotypically from other species.

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STRAINA strain is a popn of organisms which are considered

to have descended from a single organism as found in a natural habitat, in primary culture and in sub cultures.

Strains in a species may differ slightly e.g. biovars , morphovars , serovars.

Type strain is the first strain studied and more fully x-terized than other strains.

A type strain must remain with in the genus of which it is the nomenclatural type, only those strains very similar to the type species are included in the species.

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Classification systemsOnce taxonomically relevant x-tics have been collected, they

may be used to construct a classification:

Natural classification (developed by Linnaeus), considers just the overall similarity/observable traits,basically anatomical traits (phenetic classification).

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)

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Systems contd….Phylogenic/phyletic classification

Involves study of evolutionary r/ships among groups of organisms which are discovered through molecular sequencing data and morphological data matrices.

Polyphasic taxonomy.

This considers the phenotype,genotype, molecular sequences, evolutionary x-tics , and ecological behaviors in classification of the organisms

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Bacterial Nomenclature The rules are set in International code for the

nomenclature of Bacteria. Bacteria are named according to binomial system

developed by Carl Von Linne/Linnaeus A species is designated with two latinized names i.e. genus

and species The first name is capitalized, second is not capitalized

(Escherichia coli). Taxonomic names approved by the International

committee of systematic Bacteriology are considered official and binding.

Bergey’s Manual of systematic Bacteriology contains the accepted system of prokaryotic taxonomy

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IDENTIFICATION OF MEDICALLY IMPORTANT BACTERIAKey parameters used:

Cell wall (rigid, flexible, or absent).

Intracellular or extracellular.

Shape of the organism.

Staining reaction.

Spore forming abilities.

Biochemical reactions.

Genetics. (rRNA sequences, hybridization, gene probes)

Cultural x-tics (diameter, outline, elevation,colour etc)

The ability to grow in absence or presence of oxygen

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Bacteria

Thick walled

Extracellular

Gram positive

Coccie.g.Streptococcus,Staphylococo

ccus

rods

Spore forming

Aerobic e.g.

bacillus

Anaerobice.g.clostridium

Non spore

forming

Filamentous e.g. Actinomyces,Nor

cardia

Non Fillamentous-Corynebacteriu

m, Listeria

Acid fast e.gMycobacteriu

mGram

negative

Cocci-Nisserias

rods

Fucultative

straight

Resp organism-Haemophillus,Bord

etella,Legionella

Zoonotic,-Brucella,Pasteurella,Yer

sinia

Enteric-Escherichia,Enterobacter,Serratia,Sal

monella

Curved-Vibrio,Helicobact

er

Aerobic-pseudom

onas

Anaerobic-Bacteriode

s

Obligate intracellular

e.g.Rickettsia , Chlamydia

Flexible thin walled e.g.Trepon

ema, Borreila

Wall less e.g. Mycoplasma

References Microbiology 5th edition (Lansing M. Prescott)

Lange microbiology and immunology review 10th

edition (Warren Levinson)

Brocks biology of Microorganisms (Madigan, Martinko etal..)

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