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Characteristics of Colonies
Size, color, texture, elevation, form, and margin are used to describe colonies on a plate.
CFU/mL Determination
CFU/mL = (# colonies/mL plate) * dilution factor; choose plates with 30-200 colonies; mL plated = 0.1mL; dilution factors:10^-5, 10^-6, 10^-7, 10^-8.
Selective and Differential Media
Chromagar selects for gram + bacteria (pink colonies) and differentiates them from gram - bacteria (colorless/blue colonies).
Hemolysins
Enzymes that break down cell membranes; types include beta-hemolysis (complete), alpha-hemolysis (partial), and gamma (none).
Gram Staining
Differentiates bacteria based on cell wall structure; uses crystal violet (gram + purple, gram - red/pink) and safranin.
Staphaurex Test
Detects clumping factor in Staph A; positive for Staph A, negative for Streptococcus pneumoniae and E. coli.
Catalase Test
Detects catalase enzyme; positive for Staph A and E. coli, negative for Streptococcus pneumoniae.
Kirby-Bauer Method
Disk diffusion test to determine bacterial sensitivity to drugs; "Zone of Inhibition" is the area where bacteria do not grow.
MacFarland Standard
Standardized inoculum density for Kirby-Bauer Method to ensure consistency in bacterial distribution on agar.
Antibiotic Targets
Penicillin targets peptidoglycan cell wall, cefoxitin targets peptidoglycan cell wall, erythromycin targets ribosome for protein synthesis.
Note
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