Comparison of Simple and Rapid Methods for Identifying Enterococci Intrinsically Resistant to Vancomycin

Abstract

ABSTRACT Three different methodologies, reduction of litmus milk (LM) and acidification of arabinose (ARA), acidification of methyl-α- d -glucopyranoside (MGP), and rapid motility (RM), for differentiating isolates of Enterococcus casseliflavus and Enterococcus gallinarum (intrinsically vancomycin-resistant enterococci [IVRE]) from Enterococcus faecalis and Enterococcus faecium were evaluated. All 33 isolates of E. faecalis tested reduced LM within 4 h and were negative in all other tests, while the 53 isolates of E. faecium were ARA positive only. In contrast, 45 of 46 (98%) IVRE isolates examined (26 E. casseliflavus and 20 E. gallinarum isolates) acidified MGP, 41 of 46 (89%) were LM and ARA positive, and 45 of 46 (98%) were RM positive. Acidification of MGP was therefore the single most useful test for differentiating IVRE from vancomycin-resistant E. faecium and E. faecalis ; however, a combination of LM-ARA and RM testing enabled the correct designation of organisms without the need for overnight incubation.