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10. Dynamics of Microbial Growth

1

concept

3m

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in this video, we're going to begin our lesson on measuring growth by direct cell counts. And so direct cell counting can be useful for determining the total number of cells in a culture. However, this method of direct cell counting and determining the total number of cells in a culture has a drawback because it does not distinguish between viable or living cells and dead cells. And so you will just get a total number of cells. Uh and it is going to include both viable and dead cells. And so in some cases this may be fine. However in other cases scientists are only interested in the viable cells. And so this may not be the best method if the scientist is interested only in the viable cells. And so we're going to talk about a very specific type of direct cell counting known as direct microscopic cell counts. And so um as its name implies it is going to be using a microscope. And so this is a very quick method for determining the number of cells in a culture by using this microscopic cell counting. And so what happens is a known volume of liquid uh culture is going to be added to a microscope slide and then a cover slip is going to be engraved with a grid. And this grid as you can see down below it can be used to facilitate cell counting and make the the direct cell counting a lot easier for the scientists. And so what happens is multiple areas of the grid are actually counted and you count the total number of cells within particular grids. And then what you do is you average all of those different uh grids that you had counted in order to determine the number of cells per volume. And that allows you to get the number of cells and count the number of cells. And so this is uh an image of direct microscopic sell counts. And so once again it is going to be using a microscope such as a compound light microscope here. And what you do is you put a little bit of a liquid broth onto a glass slide and you put a cover slip on it and the cover slip has a grid. And so that grid is going to be visible underneath of the microscope. And so what scientists can do is they can count different grids, say like this grid here and this grid here and this grid over here. They can count as many grids as they want and they will count the total number of cells in each grid and then they will do an average. And then by doing that, what they're able to do is determined the number of cells per volume and determine the total number of cells. And so this year concludes our introduction to measuring growth by direct cell counts, specifically by using direct microscopic cell counts. And we'll be able to get some practice applying these concepts and learn more about cell counting as we move forward in our course. So I'll see you all in our next video.

2

Problem

Direct microscopic cell counting is a method where the microbiologist counts the number of microbes in a fraction of the microbial culture to:

A

Determine the cell count for the entire microbial culture.

B

Determine the growth rate of the microbial culture.

C

Determine the death rate of the microbial culture.

D

Estimate how large the microbial culture will grow in 10 generations.

3

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in this video, we're going to talk about types of direct cell counting instruments. And so since counting cells manually using direct microscopic cell counting is really tedious and long and error prone lab instruments have been designed to directly count cells in a culture. And so a flow saitama Ter is a really fancy piece of equipment or instrument that counts cells moving through a really narrow channel and counts those cells that moved to the narrow channel and pass across a laser beam. And so cells will individually pass through that light from the laser beam, causing that light to scatter. And that scattered light uh can be detected by a cell counter. And so if we take a look at our image down below, we're showing you a little diagram here of a flow saitama Ter and so what you'll notice is that at the very top what we have is our cell sample. So we have a bunch of cells in here and uh these cells are going to be passed through a narrow channel where the cells are going to pass through this narrow channel in a single file line individually. And so these single cells are passing through this narrow channel and eventually they pass through a laser beam and the light from the laser beam is going to hit the cells as they pass through this narrow channel. And when it hits the cells it causes some of that light to scatter. And that scattered light represented here by this green arrow can be detected by a cell counter. And so the cell counter will keep track of how many cells have passed through. And so that is another way to directly count cells is by using a Flow Saitama Ter, now another instrument known as a culture counter, is very similar to a Flow Saitama Ter, but instead of counting cells by looking at scattered light from the laser beam, it's going to electronically detect the cells and it counts the cells moving through the channel as well. And so this year concludes our brief introduction to some types of direct cell counting instruments, and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.

4

Problem

Determining the number of cells within a culture is important. However, counting each and every cell with the human eye is tedious and extremely time consuming. Which of these is a method of cell counting that does not require a scientist to count each and every cell?

A

Flow cytometry.

B

Direct microscopic cell counting.

C

Coulter counting.

D

A and B.

E

A and C.

F

B and C.

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