I'm doing mic and mbc following the disc diffusion assay. I want to calculate the cfu value for the microbial growth in the plate. Can you please share any relevant article or the exact calculation?
Make serial dilution to your sample then plating on agar calculate number of colonies present on agar plate multiplied by dilution factor
The following p can help you
This depends on from which dilution you are plating and what volume you are plating. Say, you get 30 colonies from 10⁶
after plating 100 micro litre ( 1 ml), then your CFU/ml will be: 30 x 10⁷ = 3 x 10⁸ = 8.477 ( log 3= 0.477 plus log 10⁸ = 8, total 8.447). You can express either 3 x 10⁸ or log value as 8.447.
Certainly! The CFU (colony-forming unit) calculation is used to estimate the viable microbial count in a sample. Here is a step-by-step guide to calculating CFU values in the context of antimicrobial MIC (minimum inhibitory concentration) and MBC (minimum bactericidal concentration) determination using the disc diffusion assay:
1. Prepare dilutions: Dilute your microbial culture to obtain a suitable concentration for plating. The dilution factor will depend on the expected microbial count and the ability to obtain countable colonies on the agar plate.
2. Plate the diluted culture: Using a sterile spreader or a pipette, spread a known volume (e.g., 0.1 mL) of the diluted culture onto agar plates. Ensure the spread is even and covers the entire plate surface.
3. Incubate the plates: Place the agar plates in an incubator under appropriate conditions for the growth of the specific microorganism (e.g., temperature, atmosphere, duration).
4. Count the colonies: After incubation, examine the plates and count the visible colonies. It's important to select plates with colonies within the countable range (typically 30-300 colonies) to ensure statistical accuracy.
5. Calculate CFU: Multiply the colony count by the dilution factor used in step 1 to obtain the CFU per mL or per gram of the original sample.
For example, if you plated 0.1 mL of a 1:100 dilution and counted 100 colonies, the CFU/mL would be 100 × 100 = 10,000 CFU/mL.
Regarding relevant articles, I don't have direct access to specific research papers, but you can search scientific databases such as PubMed or Google Scholar using keywords like "CFU calculation," "colony-forming unit calculation," or "microbial count calculation" to find articles that provide more detailed information and examples.
good luck,
Your enumeration of microbes as Colony Forming Unit ( CFU), you should be very perfect what type of microbes you are dealing with. Accordingly you should proceed serial dilution pour plate or spread plate technique. For instance, if you are dealing with bacteria, your accurate dilution will be 10‐⁴, 10-⁵ and 10-⁶ . Suppose you get 30 colonies in 10-⁵ by inoculating 0.1 ml, Then your CFU will be average count x dilution factor and find out as CFU per ml or per gram as follows: 30 x 10⁵= 3x 10⁶ for 0.1 ml So CFU per ml will be 3 x 10⁷. It is better to express as log value. Your answer is 7. 477. Why log value? Because exponential growth of bacteria is always in log phase. If you deal with Actinobacteria , go one step lower dilution I.e., your sampling will be 19³, 19⁴ and 10⁵ ( because Actinobacterial population is less than bacteria in normal soil). Similarly, when you deal with fungi, choose the dilution 19², 19³ and 10⁴. Hope, I could clear your doubt.
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