Lab Quiz 2 Review

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.