Evaluation of MicroScan for identification of Enterococcus species

Emerging drug resistance of the enterococci necessitates differentiation from group D streptococci and accurate species identification. MicroScan (Baxter Healthcare Corp., West Sacramento, Calif.) has recently developed a microdilution system for identification and antibiotic susceptibility testing of gram-positive cocci. To evaluate the ability of this system to identify Enterococcus species, 100 isolate identified as enterococci by MicroScan were tested by conventional media and 60 isolates of streptococci were tested by MicroScan. Incubation times for conventional and MicroScan methods were 96 and 18 to 24 h, respectively. For 94 strains of enterococci (77 Enterococcus faecalis, 14 Enterococcus faecium, and 3 Enterococcus durans), identification by conventional media and MicroScan agreed. Of the remaining six isolates, four were identified as E. faecalis and two were identified as E. durans by MicroScan, whereas by conventional media the four E. faecalis isolates were identified as Enterococcus solitarius and the two E. durans isolates were identified as Enterococcus hirae. None of the 60 streptococci were identified as enterococci. MicroScan is a reliable method for identification of the commonly encountered enterococcal species E. faecalis and E. faecium; however, modifications of the system are necessary for identification of other Enterococcus species.