Measuring Growth by Membrane Filtration - Online Tutor, Practice Problems & Exam Prep

Membrane filtration is a technique used to measure microbial growth by trapping viable cells from liquid cultures through a filter with pores smaller than the cells. A known volume of culture is passed through the filter, capturing the cells, which are then incubated on an agar plate to form colonies. Counting these colonies, or colony-forming units (CFUs), provides an estimate of the original viable cell count. This method is essential for quantifying microorganisms in various applications, including environmental monitoring and clinical diagnostics.

Measuring Growth by Membrane Filtration

In this video, we're going to begin our lesson on measuring microbial growth by membrane filtration. Membrane filtration is a process that's used to count the number of viable cells or living cells in liquid cultures with only a few cells, and so a small number of cells are required. Now, in this process of membrane filtration, a known volume of liquid culture is going to be passed through a membrane filter. This membrane filter has really, really small pores in it, even smaller than cells themselves. As a result, the cells will actually get trapped in the membrane filter. Colonies will begin to form after the membrane filter with the trapped cells is transferred to an agar plate and incubated, and counting the colonies that form gives the total number of viable cells or living cells in the original liquid culture.

Let's take a look at this image down below to get a better understanding of membrane filtration of microbes. On the left-hand side over here, what we're showing you is this filter here, and this red sheet that you hear is the membrane filter paper, which has all of those tiny pores in them, which can be used to trap cells. What you do is pour the liquid culture right into the top of this filter here, and the vacuum that's created down below will filter all of the liquid through. However, the cells remain trapped in the membrane filter. You can remove the membrane filter and place it into a petri dish with solid growth media, which will allow for microbial growth to occur. What you'll see here are the actual colonies forming, and these colonies once again represent colony-forming units, and so they represent individual viable cells.

This concludes our brief lesson on measuring growth by membrane filtration. 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.

Microbial cell colonies can be grown on a solid growth medium or within a liquid growth medium. If you wanted to count the number of bacteria cells in a small colony found in a liquid broth, which counting technique would you use?

• A. Flow cytometry.
• B. Coulter counting.
• C. Membrane filtration.
• D. Direct microscopic cell counting.
• E. None of the above.

Many forms of technology have been invented to prevent microbiologists from having to count each and every individual bacterial cell they are studying. Which form of technology is able to count the number of cells in a bacterial population using a laser beam?

• A. Flow Cytometer.
• B. Membrane Filtration.
• C. Coulter Counting.
• D. Plate Counting.

Here’s what students ask on this topic:

What is membrane filtration in microbiology?

Membrane filtration is a technique used in microbiology to measure microbial growth by trapping viable cells from liquid cultures. A known volume of the liquid culture is passed through a membrane filter with pores smaller than the cells. These cells get trapped in the filter, which is then transferred to an agar plate and incubated. The colonies that form on the agar plate represent colony-forming units (CFUs), which can be counted to estimate the number of viable cells in the original culture. This method is crucial for applications like environmental monitoring and clinical diagnostics.

How does membrane filtration work to measure microbial growth?

In membrane filtration, a known volume of liquid culture is passed through a membrane filter with very small pores. These pores are smaller than the microbial cells, causing the cells to get trapped on the filter. The filter is then placed on an agar plate and incubated, allowing the trapped cells to grow into colonies. By counting these colonies, or colony-forming units (CFUs), one can estimate the number of viable cells in the original liquid culture. This method is particularly useful for samples with low cell concentrations.

What are the applications of membrane filtration in microbiology?

Membrane filtration has several important applications in microbiology. It is widely used in environmental monitoring to detect and quantify microorganisms in water and air samples. In clinical diagnostics, it helps in identifying and counting pathogens in bodily fluids. The technique is also employed in the food and beverage industry to ensure microbial safety and quality. Additionally, it is used in pharmaceutical manufacturing to test for microbial contamination in products.

What are colony-forming units (CFUs) in the context of membrane filtration?

Colony-forming units (CFUs) are a measure used in microbiology to estimate the number of viable cells in a sample. In the context of membrane filtration, CFUs refer to the colonies that form on an agar plate after the membrane filter, with trapped cells, is incubated. Each colony originates from a single viable cell or a group of cells, making CFUs a reliable indicator of the number of living microorganisms in the original liquid culture.

Why is membrane filtration important for environmental monitoring?

Membrane filtration is crucial for environmental monitoring because it allows for the detection and quantification of microorganisms in water, air, and soil samples. This technique is sensitive enough to identify low concentrations of microbes, making it ideal for assessing water quality, detecting contamination, and monitoring microbial populations in various environments. By providing accurate counts of viable cells, membrane filtration helps in ensuring public health and environmental safety.