The key difference between agar well and disc diffusion method is that in agar well diffusion method, the extract solution is filled into a hole or a well created on the agar medium while in agar disc diffusion method, a filter paper disc containing the test solution is placed on the agar surface.
Microorganisms are the agents of many diseases. There are different antimicrobial agents that kill microorganisms and inhibit or arrest their growth. Various screening and evaluating methods are available for the detection of antimicrobial activity. Among them, agar well diffusion method and agar disc diffusion methods are commonly used methods in in vitro analysis, which are agar diffusion methods. These methods are widely used since they do not require specified equipment and further evaluation for reproducibility and standardization. Both methods depend on the diffusion of the antimicrobial agent through the agar medium.
CONTENTS
1. Overview and Key Difference
2. What is Agar Well Diffusion Method
3. What is Agar Disc Diffusion Method
4. Similarities Between Agar Well and Disc Diffusion Method
5. Side by Side Comparison – Agar Well vs Disc Diffusion Method in Tabular Form
6. Summary
What is Agar Well Diffusion Method?
Agar well diffusion method is one of the cheapest and easiest in vitro antimicrobial activity tests. Using this method, plant extracts and microbial extracts can be screened for antimicrobial activity against pathogenic microbial species. In this method, an agar plate is v inoculated by a pathogenic bacterial species using the spread plate technique. This is done by spreading a known volume of the microbial solution over the surface of the agar using a glass spreader. Then a hole or a well (diameter of 6 to 8 mm) is created aseptically with a sterile cork borer. Next, the well should be filled with the extract solution (test solution), and then the plates should be incubated at a suitable temperature and suitable conditions. When incubated, the antimicrobial extract solution gradually diffuses through the agar medium and inhibits the growth of the bacterial species tested. Finally, the inhibition zone can be observed, and the diameter of the zone is taken as a measurement.
What is Agar Disc Diffusion Method?
Similar to the agar well diffusion method, the agar disc diffusion method is also a routinely used antimicrobial susceptibility testing method in laboratories. In this method, a filter paper disc which contains the test solution is kept on the agar medium. Prior to that, the agar plate should be inoculated with the test microorganism. Then the filter paper disc, which contains a known concentration of the extract solution, is placed on the agar medium. Then the plates are incubated under suitable conditions.
Figure 02: Agar Disc Diffusion Method
When incubated, the extract solution diffuses through the agar medium and inhibit the microbial growth. After incubation, the diameter of the inhibition zone is measured and compared.
What are the Similarities Between Agar Well and Disc Diffusion Method?
- Agar well and disc diffusion methods are two types of antimicrobial susceptibility testing methods which are agar diffusion methods.
- Both methods are easy to perform and cost-effective.
- They are routinely done in the laboratories.
- Therefore, they are in vitro
- It is possible to test several microbes or several extracts easily with both these methods.
- The result interpretation is also easy in both methods.
- Furthermore, they do not require specific types of equipment.
- But both methods are unable to distinguish bactericidal and bacteriostatic effects.
- Moreover, both methods are not appropriate to determine the minimum inhibitory concentration.
What is the Difference Between Agar Well and Disc Diffusion Method?
Agar well diffusion method is the antimicrobial activity test in which a hole is created in the agar medium, and the extract solution is added to it. Meanwhile, the agar disc diffusion method is an antimicrobial activity test in which a filter paper disc containing the known concentration of the extract solution is placed on the agar medium. So, this is the key difference between agar well and disc diffusion method. Therefore, extract solution is added to the agar well or hole in agar well diffusion method while the extract solution is added to the filter paper disc in the agar disc diffusion method. Hence, agar well diffusion method does not use filter paper disc while the agar disc diffusion method does not create agar holes in the agar medium.
Before is a side by side comparison of the difference between agar well and disc diffusion method.
Summary – Agar Well vs Disc Diffusion Method
Agar well and disc diffusion methods are two types of antimicrobial susceptibility testing methods. Both methods are simple and low cost in vitro methods. In agar, well diffusion method, a hole or well is created on the medium, and then the extract solution is added to the well in order to assess the antimicrobial activity. In contrast, in the agar disc diffusion method, the extract solution is added to a filter paper disc and then placed on the agar surface. So, this is the key difference between agar well and disc diffusion method.
Reference:
1. Balouiri, Mounyr, et al. “Methods for in Vitro Evaluating Antimicrobial Activity: A Review.” Journal of Pharmaceutical Analysis, Elsevier, 2 Dec. 2015, Available here.
Image Courtesy:
1. “Agar Diffusion Method 1” By Sommer36 – Own work (CC BY-SA 4.0) via Commons Wikimedia