FIG. 1.

Population analysis of VRSA, VISA, hVISA, and VSSA. The population analysis shows how many cells in a fixed number of cells (usually about 10⁷ CFU) of each strain are resistant to various concentrations of vancomycin. VRSA is a highly resistant and homogeneously resistant strain with 100% of the population growing at each of the vancomycin concentrations tested. VISA is intermediately resistant with 100% of the population growing at 4 μg of vancomycin per ml and also with significant subpopulations growing at 8 μg/ml. hVISA demonstrates heterogeneous resistance, having subpopulations of cells with various levels of resistance to vancomycin and including small populations of vancomycin-intermediate resistant cells with growth at 8 μg of vancomycin per ml.