How would you determine the minimum bactericidal concentration of a given microbial agent?
I assume you are referring to the MBC of an anti-microbial agent.
Generally it is determined by subculturing on agar plates, and much of the time, by counting colonies.
MBC is the minimum concentration to kill ≥99.9% of a given bacterium. Do not confuse with MIC (minimum inhibitory concentration) which inhibits growth.
The detailed laboratory procedures may be found, for example, in scholastic journals such as:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC184632/pdf/aac00202-0158.pdf
or
http://s3.amazonaws.com/academia.edu.documents/34265897/Determination_of_MICs.pdf?AWSAccessKeyId=AKIAIWOWYYGZ2Y53UL3A&Expires=1496576641&Signature=BvkOPLAnYFEeV1kepufARpnMOMA%3D&response-content-disposition=inline%3B%20filename%3DJAC_Determination_of_minimum_inhibitory.pdf
To determine the minimum bactericidal concentration (MBC) of a microbial agent, the following steps can be followed:
1. Prepare a series of test tubes or wells containing a growth medium: Use a suitable medium that supports the growth of the target microorganism. The number of tubes/wells depends on the number of concentrations you want to test.
2. Add different concentrations of the microbial agent: Prepare a range of concentrations of the microbial agent, starting from a high concentration and diluting it serially. Each tube/well should have a different concentration.
3. Inoculate the test tubes/wells: Add a standardized amount of the target microorganism to each tube or well containing the different concentrations of the microbial agent.
4. Incubate the tubes/wells: Place the tubes/wells in an incubator at the optimal temperature for the growth of the microorganism. Incubate for a suitable time period to allow the microorganism to grow and exhibit sensitivity to the microbial agent.
5. Observe the growth: After incubation, visually inspect each tube or well for visible growth of the microorganism. Growth may appear as turbidity or colony formation.
6. Determine the MBC: The MBC is the lowest concentration of the microbial agent that shows no visible growth of the microorganism. The tube or well with this lowest concentration is the MBC.
It is worth mentioning that in some cases, the MBC cannot be determined by visual observation alone. Additional tests, such as subculturing, may be needed to confirm the absence of viable microorganisms.