Evaluation of D-xylose and 1% methyl-alpha-D-glucopyranoside fermentation tests for distinguishing Enterococcus gallinarum from Enterococcus faecium

To determine the validity of the rapid xylose and methyl-alpha-D-glucopyran oside (MDG) fermentation tests in distinguishing Enterococcus gallinarum fr om Enterococcus faecium, 156 well-characterized clinical isolates of entero cocci (55 E. gallinarum, 91 E. faecium, and 10 Enterococcus faecalis isolat es) known to be of different clones were examined in a blinded fashion. Spe cies identification was confirmed by PCR of the ddl ligase genes of E. faec ium and E. faecalis and the vanC1 gene of E. gallinarum. Xylose tests were performed with D-xylose tablets by using a heavy bacterial suspension and w ere interpreted after 2 h of incubation. Standard MDG fermentation tests we re read after 24 h of incubation. The xylose fermentation test had a sensit ivity of 98% (54 of 55) and a specificity of 99% (100 of 101) in distinguis hing E. gallinarum from E. faecium and E. faecalis. The standard MDG test h ad a sensitivity of 100% (55 of 55) and a specificity of 95% (96 of 101) af ter 24 h. The xylose fermentation test is a simple method, easily incorpora ted into laboratory protocols, that distinguishes E. gallinarum from E. fae cium with high sensitivity and specificity in 2 h. The standard MDG test ha s high sensitivity and can be useful in ruling out the presence of E. galli narum but requires overnight incubation.