Figure 1.

Deletion of stp1 results in reduced vancomycin susceptibility in Staphylococcus aureus. (A) Vancomycin minimum inhibitory concentrations (MICs) were determined by Etest for A5937, A5937Δstp1, the complemented strain A5937Δstp1-C, and the vancomycin nonsusceptible isolate A5940. Values in parentheses represent MICs based on broth dilution. (B) Determination of vancomycin heteroresistance was performed using population analysis profiling. The stp1 deletion mutant had subpopulations that grew in the nonsusceptible range (>2 µg/mL); this was not seen in the parent strain (A5937) but was more pronounced in the clinical vancomycin-intermediate S. aureus daughter strain (A5940). CFU, colony-forming unit. (C) Transmission electron microscopy was performed to determine cell wall thickness. Three representative cells from each strain are shown, and values represent mean cell wall thickness (95% confidence interval). A5940 had the thickest cell wall, followed by the A5937Δstp1 and finally A5937.