Single dye fluorescent staining and the combination of differences in both intensity and spectral emission permit determination of the minimum concentration of an antibiotic needed to inactivate bacteria (Minimum Inhibitory Concentration (MIC)), thereby providing a means for rapid Antibiotic Susceptibility Testing (AST). This allows for a quick and easy means for clinicians to determine a suitable treatment regimen for patients suffering from bacterial infections and those that eventually lead to sepsis.