Antibacterial activity of Vatica diospyroides fruit extracts were screened against both Gram-positive and Gram-negative bacteria using disc diffusion method. Minimum Inhibitory Concentrations (MICs) were performed using a macro broth dilution assay. Bacteria were treated with the extracts at various dose levels (0.5, 1, and 2 MIC) and incubation times (3 and 6 h), and their responses were monitored by FACS analysis. The response patterns were analyzed in the counts of 4 subpopulations: viable cells (PI-, SSC-), membrane-damaged cells (PI+, SSC-), injured cells (PI-, SSC+), and dead cells (PI+, SSC+). The fraction of Bacillus subtilis responders to fruit cotyledon and pericarp extracts increased in a dose dependent manner, whereas Staphylococcus aureus treated with pericarp extract increased in a time dependent manner. Cells initially lost granularity (PI-, SSC+) and membrane integrity (PI+, SSC+). These results demonstrate that the FACS method can reveal the stages of bacterial responses to chemotherapeutic agents.