Microscale assay to evaluate the minimum inhibitory concentration of purified compounds with limited sample volume

The minimum inhibitory concentration (MIC) is a standard measure for describing the lowest effective dose concentration of an antimicrobial compound in clinical practice; yet, conventional assays often require a substantial amount of antimicrobial compound, limiting their use with scarce, purified agents. Here, we describe a simple and reproducible technique to evaluate the MIC for purified compounds with a limited sample size. The protocol describes the MIC steps against a bacterial strain while minimizing the use of reagents and materials. It is helpful for screening purified natural products as antimicrobial agents and in early-stage drug discovery. The protocol adapts standard microplate-based assays for two-fold dilution of the compound, ensuring their applicability in microbiological studies. The MIC value of the standard antibiotic kanamycin against Staphylococcus aureus, Vibrio fischeri, Klebsiella pneumoniae, and Escherichia coli was determined using our method, and was found to be consistent with the conventional broth microdilution method, validating its reliability. Therefore, this method offers a practical and viable solution for antimicrobial drug discovery, addressing the disparity between limited compound availability and comprehensive microbiological assessment of MIC.