Lab 11: Carbohydrate Metabolism

Lab 11: Carbohydrate Metabolism Notes

Introduction to Bacterial Identification

Streak Plate
Purpose: Isolate bacteria for single colony growth.

Colony Definition: Mass of identical bacteria.

Colony Morphology: Color, size, shape, texture.

Gram Staining
Purpose: Determine cell wall type (Gram-positive or Gram-negative).

Cell Shape: Cocci (spherical), bacilli (rod-shaped), spiral.

Importance: Narrows identification.

Understanding Gram Stains

Gram-positive: Excludes Gram-negative.

Shape: Coccus excludes bacillus/spiral.

Results narrow, don't confirm identity.

Biochemical Profiling

Biochemical Profile: Enzyme reactions bacteria perform.

Compares unknown profile to known bacteria.

Metabolism: All cell reactions, including:
Anabolic Reactions: Synthesis.
Catabolic Reactions: Breakdown for energy.

Focus: Carbohydrate Metabolism

Process: Converts carbs to ATP.

Waste Product: Acidic (vs. alkaline protein metabolism).

Aim: Test bacteria's ability to degrade carbs for ATP.

Indicators for Carbohydrate Utilization

Phenol Red: pH indicator for glucose, lactose, sucrose, mannitol.

Color Change: Red (pH 7.4), Yellow (acidic), Pink (alkaline).

Observations: Yellow = sugar utilization.

Glucose test: Durham tube for gas.

Examples:

Positive + gas: bubble.
Positive - gas: yellow, no bubble.
Negative: red medium.

Additional Tests

Starch Hydrolysis: Tests starch breakdown.

Indicator: Iodine.
Appearance: Brown, Black (with starch).

Observations: Light brown around growth = starch breakdown.

Methyl Red - Voges-Proskauer (MR-VP):
Indicators: Methyl Red