Transmission electron microscopy of initial isolate (SaB1)-VSSA vs. after persistent bacteremia isolate (SaB2)-h-VISA. Comparison of the cell thickness among the pair of strains (SaB2 vs SaB1) and one derivative VISA (CIM 4 μg/ml) obtained on PAP (PAPd4). Quality control strains included S. aureus ATCC 29213 and Mu50, control, negative and positive for VISA, respectively. Magnification: × 60,000. Values given under each image are mean ± SD of the cell wall thickness in nanometers. Student's t test demonstrated that this augment in cell wall thickness was statistically significant (p < 0.001).