Techniques for classification

Techniques for classification

1. Classical characteristics

   • Morphological characteristics
     • e.g. cell shape, cell size, colony colour
   • Physiological and metabolic characteristics
     • Activity of enzymes and proteins
   • Biochemical characteristics
     • FAME for analysis of bacterial fatty acids
   • Ecological characteristics
     • e.g. life cycle pattern, habitat preferences

2. Molecular characteristics

   • Methods for identification
     • Microscopic identification
       • Bright field
       • Phase contrast
       • Dark field
       • Electron microscope
       • Fluorescence
     • Growth and biochemical characteristics
       • Biochemical test systems
         • API kits ( carbohydrate fermentation)
         • API zym
       • Immunologic systems
       • Automated systems
     • Immunologic test
       • Detection of antibodies induced by the microorganisms
       • Disadvantages
         • variable immunologic response
         • lack of measurable antibody titer
         • Immunosuppressed
       • Specific and sensitive
     • Bacteriophage typing
       • specific phage attack specific bacteria
     • Antibiotics susceptibility test
       • determine the pattern of resistance or susceptibility to antibiotics
       • Method
         • Dilution susceptibility test
         • Agar dilution test
         • Disc diffusion test
   • Determination of DNA base composition
     • G/C content
       • HPLC
       • Melting temperature of DNA
       • not able to determine the arrangement of G/C
   • Comparison of amino acid sequences
     • if similar sequence of proteins with same function, both organisms are related
     • Disadvantage
       • Expensive
       • Slow
   • Nucleic Acid sequencing
     • Sequencing of rDNA
   • Genomic fingerprinting
     • MLSA
     • RFLP
       • If specific gene is the 16S rRNA, the technique is known as ribotyping
   • Nucleic acid hybridization
     • complete hybridization
       • Organism identical
     • Partial hybridization
       • Organism related
     • No hybridization
       • Organism unrelated
   • REP-PCR
     • The same sequence appear repetitively, therefore the bands appear in different size
   • Nucleic acid probes
     • positive hybridization will produce signal
     • negative hybridisation will not produce signal
   • Plasmid fingerprinting
     • provide the differential characteristics for strains