Light scatter (using spec)
Direct count is a straightforward way to figure out how many meningicocci Frank is harboring, but it is a bit labor intensive. Wouldn't it be nice to get a machine to do the counting for us?
One way we can do this is to use a photospectometer. A spec doesn't exactly count the cocci, but it does measure how much they interfere with a light beam, and based on that, we can use a calibration to decide how many cocci we've got. Then we can do the scaling up trick to get the total population size.
This is a great method if you already have a calibration curve -- perhaps you work in a lab that has been studying this critter for years... Otherwise, you may need to spend a couple of days doing the calibration (growing the cultures, taking the spec readings, comparing them to counts under the microscope... that sort of thing).
Here's an example of a calibration curve:
For example, if you prepared a sample and got a spec reading of 0.5, you would find 0.5 on the x-axis and read the bacterial count off the y-axis -- about 26 million
How about a spec reading of 0.9? (Be careful with the log scale for bacteria!!)
If your sample had about 12 million bacteria, what OD reading would you expect?
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