Bacterial taxonomy, pixel copy (2)


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Bacterial taxonomy, pixel copy (2)

  1. 1. BY MWEBAZA IVAN Msci I 2013/HD07/767U 10/1/2013
  2. 2. 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) 10/1/2013
  3. 3. 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. 10/1/2013
  4. 4. 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. 10/1/2013
  5. 5. BACTERIA Have no membrane bound organelles, Have single circular DNA. Transcription and translation can be carried out simultaneously. Have diacyl glycerol diester lipids in their membranes. 10/1/2013
  6. 6. 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. 10/1/2013
  7. 7. Classification of Bacteria Bacteria 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. 10/1/2013
  8. 8. STRAIN A 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. 10/1/2013
  9. 9. Classification systems Once 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) 10/1/2013
  10. 10. 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 10/1/2013
  11. 11. 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 10/1/2013
  12. 12. IDENTIFICATION OF MEDICALLY IMPORTANT BACTERIA Key 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 10/1/2013
  13. 13. 10/1/2013 Bacteria Thick walled Extracellu lar Gram positive Cocci e.g.Strepto coccus,Sta phylococo ccus rods Spore forming Aerobic e.g. bacillus Anaerobic e.g.clost ridium Non spore forming Filament ous e.g. Actinom yces,Nor cardia Non Fillame ntous- Coryne bacteriu m, Listeria Acid fast e.g Mycobacteriu m Gram negative Cocci- Nisserias rods Fucultati ve straight Resp organism- Haemophillus,Bord etella,Legionella Zoonotic,- Brucella,Pas teurella,Yer sinia Enteric- Escherichia,Entero bacter,Serratia,Sal monella Curved- Vibrio,H elicobact 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
  14. 14. References  Microbiology 5th edition (Lansing M. Prescott)  Lange microbiology and immunology review 10th edition (Warren Levinson)  Brocks biology of Microorganisms (Madigan, Martinko etal..) 10/1/2013