1 / 12

Measures of Microbial Populations

Measures of Microbial Populations. Quantifying the unseen. Variety of Approaches. Direct Cell Count (DCC). Petroff-Hauser Counting chamber (Hemocytometer) and Phase Contrast Microscope Sensitvity down to 10 5 cells per ml Live cells and dead cells counted equally Motility?.

hillary-french
Download Presentation

Measures of Microbial Populations

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Measures of Microbial Populations Quantifying the unseen

  2. Variety of Approaches

  3. Direct Cell Count (DCC) • Petroff-Hauser Counting chamber (Hemocytometer) and Phase Contrast Microscope • Sensitvity down to 105 cells per ml • Live cells and dead cells counted equally • Motility?

  4. Viable Cell Count • Usually requires serial dilution of culture (sample) • Followed by plating technique • Sensitivity down to 300 cells per ml (or less) • Counts only “live” cell – Viable • Assumes each colony forms from a single cell

  5. Dilution and Dilution Factors • A small amount of liquid is dispersed evenly into a volume of diluent (e.g. PBS) • The new population density relative to the original is expressed as the dilution factor (DF) • DF is always less than 1, and a unit-less number (ratio)

  6. Serial Dilutions • To greatly reduce a population density, dilutions are made from dilutions! • This series of dilutions is referred to as a serial dilution • The serial dilution factor is just the product of the individual dilution factors

  7. Plating • Samples and their dilutions are applied to some solid media so that individual colonies will arise • Spread plate technique and pour plate technique

  8. Counting Spread Plates • Quebec Colony Counter • Each colony may arise from a single cell or a group of cells (chain, tetrad, etc.) • Colony Forming Unit – CFU • Accurate range 30-300 CFU • <30 sample size too small • >300 too close to individuate TNTC

  9. VCC

  10. Optical Density – A Bright Idea • Spectrophotometer is used to measure how much light is blocked out by bacteria in suspension • We will use OD units (absorbance) rather than Klett Units

  11. Correlation Between OD and VCC • Due to size and shape the amount of light blocked out is unique to each species • One must develop a correlation between Absorbance and CFU per ml (basically the slope of graph b)

  12. Today’s Exercise • Perform dilution and plating as per lab handout • Measure theOD600 of your culture • Divide CFU per ml (result 1) by the OD600 (result 2) to obtain CFU per ml per OD

More Related