BIO 411 – Medical Microbiology Chapter 2 Bacterial Classification

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

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

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

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

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

Classification Schemes Boxes 2-4 through 2-8