1. BIO 411 – Medical Microbiology
Chapter 2
Bacterial Classification

2. Phenotypic Classification
Microscopic morphology
Gram stain reaction
Shape and arrangement
Macroscopic morphology
Blood hemolysis
Colony shape and size
Pigmentation
Odor

3. Phenotypic Classification
Streptococcus pyogenes example:
Gram +
Forms long chains of cocci
Shows complete blood hemolysis
Small, white colonies
But this usually isn’t enough info. to ID the organism
Additional info. must be obtained

4. Phenotypic Classification
Biochemical Tests
Carbohydrate fermentation
Carbon source utilization
Presence of specific enzymes (proteases, nucleases, lipases, etc.)
This usually gives enough info. to ID most human pathogens
Some species can even be broken into sup-categories using biochemical tests.
This technique is called biotyping

5. Phenotypic Classification
Many bacteria possess antigens that are unique and can be used for ID
This technique is called serotyping
E. coli O157
S. pyogenes

6. Genotypic Classification
Genotypic Classification Methods
G-C ratio
DNA hybridization (with species-specific probes)
Sequence analysis
PCR

7. Classification Schemes
Boxes 2-4 through 2-8