Quantitative Measurement of Bacterial Growth

Quantitative Measurement of Bacterial Growth involves measuring either the total cell counts or the viable cell count.

Total Cell Count Methods

Counter Chamber Method (Hemocytometer)

• Description: A manual counting method using a specialized slide with a grid.

• Procedure:

  1. A known volume of bacterial suspension is placed on the hemocytometer grid.
  2. The grid is viewed under a microscope.
  3. Cells within the grid areas are counted.
  4. The total cell concentration is calculated based on the grid volume and dilution factor.
• Advantages: Simple, inexpensive, provides immediate results.
• Disadvantages: Cannot differentiate between live and dead cells, time-consuming, subject to human error.

Electron Counter Method (Coulter Counter)

• Description: An automated device that counts cells by measuring changes in electrical resistance.

• Procedure:

  1. The bacterial suspension is passed through a small aperture.
  2. As cells pass through the aperture, they disrupt an electrical current, causing changes in resistance.
  3. Each disruption is counted as a cell.
• Advantages: Rapid, automated, and precise.
• Disadvantages: Expensive equipment, cannot differentiate between live and dead cells, requires maintenance.

Viable Cell Count Methods

Plate Count Method (Colony Forming Units – CFUs)

• Description: A method to count viable bacteria by growing colonies on agar plates.

• Procedure:

  1. A known volume of a diluted bacterial suspension is spread on an agar plate.
  2. The plate is incubated to allow colony formation.
  3. Colonies are counted, and the number of viable cells is calculated based on the dilution factor.
• Advantages: Only counts viable cells capable of forming colonies, widely used, relatively simple.
• Disadvantages: Time-consuming (requires incubation), may underestimate cell count if cells clump together or are non-culturable under the given conditions.

Membrane Filter Count Method

• Description: A method to count viable bacteria in liquid samples by filtration.

• Procedure:

  1. A known volume of liquid sample is filtered through a membrane with a pore size small enough to retain bacteria.
  2. The membrane is placed on an agar plate or absorbent pad soaked with nutrient medium.
  3. The plate is incubated to allow colony formation.
  4. Colonies on the membrane are counted to calculate the viable cell concentration.
• Advantages: Useful for low bacterial concentrations, suitable for large volumes, allows for concentration of bacteria.
• Disadvantages: Time-consuming, requires filtration apparatus, may not capture all viable cells if they pass through the membrane or do not grow on the selected medium.

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