Susceptibility to desferrioxamine: a new test for the identification of Staphylococcus epidermidis

The ability to identify Staphylococcus epidermidis quickly and accurately has become increasingly important in clinical microbiology. Susceptibility to desferrioxamine, an iron-chelating agent, was investigated as a new test for the identification of S. epidermidis. All strains of S. epidermidis and S. hominis tested were susceptible to a 1000-micrograms disk of desferrioxamine when grown on brain heart infusion agar. All other strains of coagulase-negative staphylococci, S. aureus and micrococci were resistant. As a single test, susceptibility to desferrioxamine was 96.4% efficient in identifying S. epidermidis; when combined with additional tests such as alkaline phosphatase production and fermentation of trehalose, the efficiency improved to 100%. Desferrioxamine disks were easy to prepare, stable and inexpensive. The test was simple to perform and interpret and should readily find application in clinical microbiology laboratories.