BIMM 121 Lecture Notes - Lecture 6: Hemocytometer, Exponential Growth, Turbidity
26 Oct 2018
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BIMM121 Lecture 6 Notes 10/23/18
- Batch culture
o Want to use incubator that shakes to allow the cells to be distributed and have access to
enough oxygen
- Growth curve in a closed system
o Lag phase: following transfer to new media
▪ Adjustment period
▪ Very slow growth
▪ Must synthesize everything they need in the new environment
▪ Don’t see increase in number of viable cells
o Log phase: exponential growth phase
▪ Rapid growth
▪ Shortest generation time possible
o Stationary phase
▪ Nutrients are limited
▪ Cell growth slows down
▪ # living cells = # dying cells
▪ plateau, so no net increase in number
of viable cells
o death phase
▪ number of living cells decline
- Measuring microbial growth
o How can we measure and count microbes?
▪ Different methods exist, including:
• Direct counts
• Viable (living) cell counting
• Turbidity (cloudiness) measurements
o Direct counts: use hemocytometer
▪ Special slide with etched grid used
▪ Known volume is loaded onto the grid and cells are counted under a light
microscope
▪ Pros: cheap, fast, easy
▪ Cons: you can’t differentiate living vs. dead cells
▪ Called hemocytometer because most common method to count RBCs
▪ Count cells inside 2 of the 25 squares inside the big center square and average # cells
▪ Each of the squares contains 16 smaller squares
▪ Calculate # cells
o Standard plate count
▪ Count the viable (living) cell counting – serial dilutions and CFUs
• First, the culture is diluted in a series of tubes
• Dilutions are plated (spread plate method)
• After incubation, colonies are counted
