Bacterial Identification & Classification
Bacterial Identification Methods
Bergey's Manual
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
Firmicutes Gram-Positive thick-skinned cells
Tenericutes
-Class 1. Mollicutes: Bacteria that lack a cell wall (Mycoplasmas)
Gracilicutes Gram-Negative thin-skinned cells
Mendosicutes
-Class 1. Archaebacteria: Bacteria w/ atypical compounds in the cell wall & membranes
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
Class 1. Firmibacteria Gram-Positive Rods or Cocci
Class 2. Thallobacteria Gram-Positive Branching cells (Actinomycetes)
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