The agar well diffusion method is commonly employed to gauge the antimicrobial activity of plant extracts by determining the zone of inhibition, while the minimum inhibitory concentration (MIC) is used to evaluate the lowest effective concentration against microorganisms. These techniques play a crucial role in assessing the potential of plant extracts as natural antimicrobial agents.
Cold extraction using aqueous or non polar solvent or both (e.g. hydroethanolic) is a good method. Partitioning may be done. Thin layer chromatography may also be used for small-scale purification of the extracts. The antimicrobial effects can be determined using agar well diffusion method or microtube dilution methods. You can consider doing the MIC/MBC, time-kill kinetics, and others