Evolution of staphylococcus aureus under vancomycin selective pressure: The role of the small-colony variant phenotype

Staphylococcus aureus small-colony variants (SCVs) often persist despite antibiotic therapy. Against a 10⁸-CFU/ml methicillinresistant S.aureus (MRSA) (strain COL) population of which 0%, 1%, 10%, 50%, or 100% was an isogenic hemB knockout (Ia48) subpopulation displaying the SCV phenotype, vancomycin achieved maximal reductions of 4.99, 5.39, 4.50, 3.28, and 1.66 log₁₀ CFU/ml over 48 h. Vancomycin at ≥16 mg/liter shifted a population from 50% SCV cells at 0 h to 100% SCV cells at 48 h, which was well characterized by a Hill-type model (R² > 0.90).