Vancomycin-Intermediate Staphylococcus epidermidis: Curio or Omen?

In this issue, Garrett and colleagues report a case of bloodstream infection caused by a strain of Staphylococcus epidermidis that exhibited reduced susceptibility to vancomycin. 1 Two isolates, collected on different days, were tested against vancomycin in three different laboratories.In disk-diffusion assays, both isolates appeared to be susceptible to vancomycin.However, tests using the Microscan Walk-Away System (MicroScan, West Sacramento, CA) yielded minimum inhibitory concentrations (MICs) of 16 ug/mL.E-tests and broth microdilution assays yielded MICs of 8 ug/mL.Both values fall within the intermediate range for vancomycin.Strains of S epidermidis with MICs =£4 ug/mL are considered susceptible, and strains with MICs 3=32 ug/mL are considered resistant. 2Strains with values in the intermediate range are variably said to have decreased susceptibility, intermediate resistance, or increased resistance.The term vancomycin-intermediate S epidermidis, or VISE, is appealing because of its consistency with the terminology used for the original isolates of Staphylococcus aureus with similar MICs. 3 -4 Regardless of the terminology, the basic phenomenon is new to the clinical microbiology laboratory.