Lecture Notes: Measuring Microbial Growth

Introduction

• Speaker: Dr. O
• Topic: Methods to measure the number of microbes in a sample.
• Objective: Discuss direct and indirect measurement techniques.

Spectrophotometry

• Purpose: Measure turbidity (cloudiness) to estimate microbial growth.
• Equipment: Spectrophotometer
  • Calibrate with sterile nutrient broth or tryptic soy broth.
  • Measure the cloudiness or turbidity of a sample.
• Process:
  • Calibrate spectrophotometer to zero.
  • Insert sample and measure light transmission.
  • Less light transmission indicates higher turbidity.
  • Turbidity correlates with microbial growth.

Direct Cell Count

• Simplest Method: Directly count bacteria.
• Comparison: Similar to counting blood cells using a hemocytometer.
• Equipment: Petroff-Hausser Chamber
  • Known sample quantity placed in chamber.
  • Count cells in a given area under a microscope.
  • Perform calculations to determine total cell count.
• Example Calculation:
  • Count 10 cells in 0.00008 mL.
  • Estimate 1.25 million cells per mL in the original sample.

Membrane Filtration Technique

• Use Case: When the sample is dilute (e.g., pond water).
• Purpose: Concentrate microorganisms for measurement.
• Process:
  • Use a membrane filter to capture microorganisms.
  • Run sample through the filter.
  • Cultivate microbes from filter paper.
  • Determine density by dividing cell count by the volume of original liquid.

Conclusion

• Discussed three methods to measure microbial contamination and growth.
• Additional methods will be covered in a separate session.

Closing

• Goodbye Message: "Have a wonderful day, be blessed."