How would you determine the minimum bactericidal concentration of a given microbial agent?

Answer 1

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