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Bacterial Identification & Classification (Bacterial Identification…
Bacterial Identification & Classification
Bacterial Identification Methods
Physiological/Biochemical Characteristics
Analysis of the enzymes & other biological properties
Examples of tests:
Fermentation of sugats
Capacity to digest/metabolize complex polymers
Production of gas
Presence of enzymes
Sensitivity to antimicrobic drugs
Chemical Analysis
Analysis of the types of specific structural substances contained in the bacteria. Such as:
Peptides in the Cell Wall
Lipids in the Membranes
Macroscopic Morphology
Analysis of the appearance of colonies, including:
Texture
Size
Shape
Pigment
Speed & Patterns of Growth (In broth & gelatin media)
Serological Analysis
Analysis of the reaction of the immune system to the antigens present on the bacterial surface
Response facilitates identification of bacteria in specimens & cultures
Microscopic Morphology
Analysis of:
Combinations of cell shape & size
Gram-Stain reaction
Acid-fast reaction
Special structures (Ex. Endospores, granules & capsules)
Genetic & Molecular Analysis
G + C Base Composition
Analysis of the overall percentage of guanine & cytosine
Indicator of relatedness since the pair does not change rapidly
Significant differences = Genetic distinction
Ex. Escherichia (48-52% G+C) and Pseudonomas (58-70% G+C) are not closely related
DNA Analysis w/ Genetic Probes
Analysis of the exact order & arrangement of the DNA code
Hybridization allows identification of bacterial species by analyzing segments of its DNA
Probes = Small DNA/RNA fragments complementary to specific DNA squences
Test Sequence
1) Unknown test DNA are extracted & bound to special blotter paper
2) Probes are added to the blotter paper
3) After several probes are added, they are observed for visible signs of fixing
4) Binding of probes to several areas of test DNA = close correspondence
Nucleic Acid Sequencing & rRNA Analysis
Comparison in the sequence of nitrogen bases in ribosomal RNA (rRNA)
Ribosomes have the same function in all cells & are more or less stable
Any major differences in the sequence/signature of the rRNA likely indicates some distance in ancestry
Effective for differentiating general group differences & identifying differences between species
Bergey's Manual
Firmicutes
Gram-Positive thick-skinned cells
Class 1. Firmibacteria
Gram-Positive Rods or Cocci
Class 2. Thallobacteria
Gram-Positive Branching cells (Actinomycetes)
Tenericutes
-Class 1. Mollicutes:
Bacteria that lack a cell wall (Mycoplasmas)
Gracilicutes
Gram-Negative thin-skinned cells
Class 2. Anoxyphotobacteria
Gram-Negative Photosynthetic bacteria that do not produce oxygen (Purple & Green Bacteria)
Class 3. Oxyphotobacteria
Gram-Negative Photosynthetic bacteria that evolve oxygen (Cyanobacteria)
Class 1. Scotobacteria
Gram-Negative Non-photosynthetic bacteria
Mendosicutes
-Class 1. Archaebacteria:
Bacteria w/ atypical compounds in the cell wall & membranes