Please needs to explain: The relationship between the great inhibitory zone (in antibacterial activity) and the lowest or greatest MIC, Why? Thanks
This may be an incomplete answer. As far as I understand, when doing MIC, due to the liquid environment, bacteria are directly exposed to a uniform concentration of drugs, which leads to rapid and comprehensive growth inhibition. However, in doing diffusion experiments, the concentration gradient of the drug decreases with distance, and the concentration at the junction will be lower than what we actually use. At the same time, bacteria in the area without drug concentration can grow normally, which can generate a continuous supply of new cells, possibly leading to bacteria that can tolerate higher drug concentrations(It may be understood that the relative concentration of the drug per cell is low due to more bacteria than used in MIC). The above is actually my guess, I did not carry out further experiments to verify.
An additional issue with the diffusion measurements is that different compounds may diffuse at different rates both due to size, surface charge etc depending upon the external substrate, which usually is agar or agarose.
The agar well diffusion test is used for screening the antibacterial properties of drugs or plant extracts. There are some limitations on using agar well diffusion tests which concentration of drugs, the thickness of agar, diffusion of drugs through the agar and pH agar. While MIC or broth microdilution method is a confirmation method where the test microorganism will interfere directly with the plant extract. MIC is to determine the lowest inhibitory activity, of course, it is different from the agar diffusion test. Thank you.
Diffusion capabilities can be vary among different extracts, so after doing agar well diffusion, for knowing the proper result MIC is performed.
I wish to approach this question from a different angle:
The occurrence of dissimilarity between the extracts that exhibit the most substantial inhibitory zones through the well diffusion method and those possessing the lowest Minimum Inhibitory Concentration (MIC) can be attributed to several factors. The inhibitory zones observed in the well diffusion method primarily indicate the extract's potential to inhibit microbial growth in a qualitative manner. This method encompasses a broader spectrum of compounds present in the extract, which might collectively contribute to the inhibition.
Conversely, the MIC quantitatively identifies the lowest concentration of an extract that effectively inhibits microbial growth. This determination considers the potency of specific bioactive components within the extract, which may not necessarily align with the overall inhibitory zone size. Variability in compound solubility, diffusion rates, and target microorganism susceptibility further contributes to this disparity.
In summary, while inhibitory zones from the well diffusion method showcase overall inhibitory potential, the MIC reflects the concentration of specific bioactive compounds. This distinction, coupled with variations in compound behavior and microbial response, leads to the observed inconsistency between the two measures.
There are two different techniques used in microbiology to assess the antimicrobial activity of substances. While they are related, they measure different aspects of antimicrobial effectiveness, which can lead to variations in results between the two methods.
The well diffusion method involves creating wells or indentations in an agar plate inoculated with bacteria. Substances with antimicrobial properties, such as antibiotics or plant extracts, are placed in the wells. If the substance inhibits bacterial growth, it will create a zone of inhibition around the well, indicating the effectiveness of the substance against the bacteria.
On the other hand, MIC is a quantitative measure that determines the lowest concentration of an antimicrobial agent that completely inhibits the visible growth of bacteria. It is usually determined using serial dilutions of the antimicrobial agent in a liquid growth medium containing the bacteria. The lowest concentration that prevents bacterial growth is considered the MIC.
Now, it's important to understand that the well diffusion method and MIC determination may not always correlate perfectly due to several reasons:
1. Diffusion: In the well diffusion method, the antimicrobial substance diffuses through the agar from the well into the surrounding area, creating a concentration gradient. The size of the zone of inhibition depends on the diffusion rate, solubility, and concentration of the substance. However, the concentration of the substance at the edge of the inhibition zone may not be equivalent to the concentration used in the MIC determination. Thus, substances with larger inhibition zones may not necessarily have the lowest MIC.
2. Time of exposure: The well diffusion method is typically performed over a shorter period, often 24 hours, whereas MIC determination involves longer incubation times, usually 18-24 hours or more. Some substances may have a delayed or prolonged inhibitory effect, meaning they may require more time to completely inhibit bacterial growth even at lower concentrations.
3. Mechanism of action: Different antimicrobial substances have varied mechanisms of action. Some substances may exhibit a bacteriostatic effect, inhibiting bacterial growth but not necessarily killing the bacteria. Others may be bactericidal, killing the bacteria outright. MIC determination takes into account the complete inhibition of bacterial growth, whereas the well diffusion method primarily assesses the ability to inhibit visible growth within a specific timeframe.
Hope it helps:credit AI
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