Measuring Growth by Direct Cell Counts - Online Tutor, Practice Problems & Exam Prep

Direct cell counting is essential for determining the total number of cells in a culture, but it does not differentiate between viable and dead cells. Direct microscopic cell counts utilize a microscope and a grid on a cover slip to facilitate counting. Instruments like flow cytometers and Coulter counters enhance accuracy by counting cells based on light scattering or electronic detection. Understanding these methods is crucial for accurate cell quantification in microbiology and related fields.

Direct Microscopic Cell Counts

In this video, we're going to begin our lesson on measuring growth by direct cell counts. 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. You will just get a total number of cells, which is going to include both viable and dead cells. In some cases, this may be fine. However, in other cases, scientists are only interested in the viable cells. This may not be the best method if the scientist is interested only in the viable cells. We're going to talk about a very specific type of direct cell counting known as direct microscopic cell counts.

As its name implies, it is going to be using a microscope. This is a very quick method for determining the number of cells in a culture by using microscopic cell counting. A known volume of liquid culture is added to a microscope slide, and then a cover slip is engraved with a grid. This grid can be used to facilitate cell counting and make the process easier for the scientists. Multiple areas of the grid are actually counted, and you count the total number of cells within particular grids. You then average all those different grids you had counted to determine the number of cells per volume.

This allows you to count the number of cells. This is an image of direct microscopic cell counts. Once again, it is going to be using a microscope such as a compound light microscope. You put a little bit of liquid broth onto a glass slide, and you put a cover slip on it, and the cover slip has a grid. The grid is going to be visible underneath the microscope. Scientists can count different grids – 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. They then do an average. By doing that, they are able to determine the number of cells per volume and the total number of cells.

This concludes our introduction to measuring growth by direct cell counts, specifically by using direct microscopic cell counts. We'll be able to get some practice applying these concepts and learn more about cell counting as we move forward in our course. I'll see you all in our next video.

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.

Types of Direct Cell Counting Instruments

In this video, we're going to talk about types of direct cell counting instruments. Since counting cells manually using direct microscopic cell counting is really tedious, long, and error-prone, lab instruments have been designed to directly count cells in a culture. A flow cytometer is a really fancy piece of equipment or instrument that counts cells moving through a really narrow channel, and counts those cells that move through the narrow channel and pass across a laser beam. Cells will individually pass through that light from the laser beam causing that light to scatter. That scattered light can be detected by a cell counter.

Take a look at our image down below, we're showing you a little diagram here of a flow cytometer. What you'll notice is that at the very top we have our cell sample. We have a bunch of cells in here. 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. These single cells are passing through this narrow channel and eventually they pass through a laser beam. The light from the laser beam is going to hit the cells as they pass through this narrow channel. When it hits the cells, it causes some of that light to scatter. That scattered light, represented here by this green arrow, can be detected by a cell counter. The cell counter will keep track of how many cells have passed through.

Another instrument known as a Coulter counter is very similar to a flow cytometer. But instead of counting cells by looking at scattered light from the laser beam, it electronically detects the cells. It counts the cells moving through the channel as well. This concludes our brief introduction to some types of direct cell counting instruments. 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.

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.

Here’s what students ask on this topic:

What is direct cell counting and why is it important in microbiology?

Direct cell counting is a method used to determine the total number of cells in a culture. It is important in microbiology because it provides a quick and straightforward way to quantify cell populations. This method, however, does not differentiate between viable (living) and dead cells, which can be a limitation depending on the experimental needs. Accurate cell quantification is crucial for various applications, including assessing microbial growth, evaluating the effectiveness of antimicrobial treatments, and conducting research in cell biology and related fields.

How does direct microscopic cell counting work?

Direct microscopic cell counting involves using a microscope and a grid-engraved cover slip to count cells in a known volume of liquid culture. A sample is placed on a microscope slide, and the cover slip with the grid is placed on top. Scientists count the cells within multiple grid areas under the microscope, then average these counts to determine the number of cells per volume. This method is quick but does not distinguish between viable and dead cells.

What are the advantages and disadvantages of using a flow cytometer for cell counting?

A flow cytometer offers several advantages for cell counting, including high accuracy, speed, and the ability to analyze multiple parameters simultaneously. It counts cells as they pass through a narrow channel and scatter light from a laser beam, which is detected and recorded. However, flow cytometers are expensive, require specialized training to operate, and may not be suitable for all types of cell cultures. Additionally, they do not differentiate between viable and dead cells unless combined with specific viability dyes.

What is the difference between a flow cytometer and a Coulter counter?

Both flow cytometers and Coulter counters are instruments used for direct cell counting, but they operate on different principles. A flow cytometer counts cells based on light scattering as cells pass through a laser beam, while a Coulter counter detects cells electronically as they move through a channel. Flow cytometers can provide more detailed information about cell characteristics, such as size and complexity, whereas Coulter counters are generally simpler and less expensive but still effective for basic cell counting.

Why might a scientist choose direct microscopic cell counting over automated methods?

A scientist might choose direct microscopic cell counting over automated methods for several reasons. It is a cost-effective and straightforward technique that does not require expensive equipment. It is also useful for small-scale experiments or when working with limited resources. Additionally, direct microscopic cell counting allows for visual inspection of cells, which can be beneficial for identifying cell morphology and detecting contaminants. However, it is more labor-intensive and less accurate than automated methods like flow cytometry or Coulter counting.