Correlation between Reduced Daptomycin Susceptibility and Vancomycin Resistance in Vancomycin-Intermediate Staphylococcus aureus

Abstract

We present here findings of a strong positive correlation between reduced daptomycin susceptibility and vancomycin resistance in vancomycin-intermediate Staphylococcus aureus (VISA). This correlation is related to cell wall thickening, suggesting that, similar to the case with vancomycin resistance in VISA, the physical barrier of a thickened cell wall may contribute to daptomycin resistance in S. aureus.

FIG. 1.

Comparison of vancomycin and daptomycin susceptibilities for a variety of S. aureus strains with different cell wall thicknesses. (A) Vancomycin and daptomycin susceptibilities were determined using an antibiotic gradient gel assay with BHI agar that contained top concentrations of vancomycin (5 mg/liter) and daptomycin (2 mg/liter). (B) Representative transmission electron microscopy and cell wall thickness of tested strains. Magnification, ×20,700. The values given under each panel are the means and standard deviations of cell wall thickness calculated from 30 cells for each strain. The photos and data are from our previous study (9).

FIG. 2.

Regression analysis of correlation between vancomycin and daptomycin susceptibilities and between cell wall thickness and daptomycin susceptibility. A significant correlation was seen in both between vancomycin and daptomycin susceptibilities (A) and cell wall thickness and daptomycin susceptibility (B).