Feasible identification of Staphylococcus epidermidis using desferrioxamine and fosfomycin disks

Abstract

Coagulase-negative Staphylococcus spp. (CoNS) have emerged as predominant pathogens in hospital-acquired infections, as well as reservoirs of antimicrobial resistance, increasing the necessity of developing reliable methods for identification of the most frequent species. The aim of this study was to propose a simplified method for identification of Staphylococcus epidermidis. A total of 490 isolates of CoNS were identified by Bannerman's method. Taking into account distinct approaches for identification of S. epidermidis, among CoNS, we proposed the use of only two disks: desferrioxamine for the initial trial, and fosfomycin to match the final identification. Of the 320 isolates susceptible to desferrioxamine, Bannerman's method identified 238 S. epidermidis and 73 S. hominis, while we achieved identification of 239 S. epidermidis and 76 S. hominis. Compared to Bannerman's method, the method proposed here obtained a sensitivity of 99.5%, and had a positive predictor value of 99.2%. We also used a genotypic method for identification of S. epidermidis by polymerase chain reaction (PCR) targeting the tuf gene. In conclusion, the method proposed here has proved to be useful for the identification of S. epidermidis, the most frequent species of CoNS isolated from blood cultures in clinical microbiology laboratories.