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Understanding Bacterial Growth Calculations and Measurement Techniques

Learn about the different phases of bacterial growth, calculations for cell numbers and generations, and methods for measuring growth including biomass, viable counts, and total counts. Explore examples and formulas for precise calculations.

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Understanding Bacterial Growth Calculations and Measurement Techniques

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  1. Bacterial Growth • Introduction • Population vs. Cellular Growth • Exponential vs. Arithmetic Growth • Bacterial Growth - Binary Fission

  2. Bacterial Growth

  3. Bacterial Growth • Bacterial Growth Curve • Lag Phase • Log Phase • Stationary Phase • Death Phase

  4. Bacterial Growth Lag Stationary Death Log

  5. Bacterial Growth • Calculations - Number of cells • Example: Initial Cells = Number x 2 number of generations of cells

  6. Bacterial Growth Sample calculation: How many cells would be in a culture if the starting number were 100,000 and the culture was allowed to divide 5 times?

  7. Bacterial Growth • Calculations - Number of Generations • Example: Generations = log n2 – log n1/log 2 Generations = log n2 – log n1/0.301 where n = number of cells at a given time

  8. Bacterial Growth Sample calculation: How many generations have elapsed if the cell count in a culture went from 3 x 108 to 8 x 1010 in 1.5 hours?

  9. Bacterial Growth • Calculations - Generation Time • Time for single cell to double • Example: Elapsed time Generation Time = Number of Generations between n1 and n2

  10. Bacterial Growth • Calculations - Generation Time • Time for single cell to double • Example: 5 hours Generation Time = (Log 1,720,320 – log 100)/.301 = 5/((6.23 – 2)/.301) = .356 hrs or 21 min

  11. Bacterial Growth • Measurement of Growth • Biomass • Viable Counts • Total Counts • Most Probable Number (MPN)

  12. Bacterial Growth • Biomass • Dry weight • Turbidity • Metabolic Activity

  13. Bacterial Growth • Dry Weight • Mass increases in proportion to growth • Filter onto pre-weighed paper • Dry under vacuum • Time consuming but usually accurate

  14. Bacterial Growth • Metabolic Activity • Dissolved oxygen • Decrease in oxygen as cells increase • pH • Use indicator change or pH meter • Monitor a metabolite • Glucose use or ethanol production or carbon dioxide

  15. Bacterial Growth • Viable Counts • Plate counts • Membrane filters

  16. Bacterial Growth • Total Counts • Direct Microscopic Count • Most Probable Number • Electronic Counter

  17. Bacterial Growth • Most Probable Number • 5 tubes at 10 mL, 1 mL and 0.1 mL sized inoculum • Use combinations with table to calculate the most probable number • Confidence limits set range

  18. Bacterial Growth • Electronic counter • Cells move past light source in very narrow tube • Each cell passing is counted • Counts both live and dead cells so must be used before culture gets to stationary phase

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