Evaluation of a Modified Scheme for the Species Identification of Enterococci

Kim, Myungsook; Kim, Sunhee; Kang, Giyeon; Yong, Dongeun; Lee, Kyungwon; Chong, Yunsop; Kim, Shin Moo

Abstract

BACKGROUND: Rapid species identification of enterococci is necessary for optimal treatment of infected patients as they are frequently resistant to various antimicrobial agents. Minimal identification scheme is necessary to cut the laboratory cost. In this study, a minimal identification system was modified to expand the identifiable species.
METHODS
Performance of MGP test was compared to that of MIO motility test. Colonies on blood agar were used to inoculate primary identification media: SFA, BEAA, mannitol agar, tellurite agar, sorbose agar and MGP agar, which were prepared in biplates. Pigment production was tested when necessary using colonies on a blood agar. Isolates, which were not identifiable by the primary test, were inoculated to secondary test media: ADH, and arabinose-, raffinose- and sucrose-containing CTA. Vitek GPI cards were used to test isolates with a doubtful identification or no identification.
RESULTS
MGP test was selected for the modified scheme, as it was more rapid and accurate than motility test. Among the 879 clinical isolates of enterococci, 462 (52.6%) and 3 (0.3%) were identified as E. faecalis and E. casseliflavus, respectively, by the primary test only. With the additional secondary tests, 379 (43.1%) isolates were identified as E. faecium. Vitek test showed the identification of 4 isolates with atypical test results and 5 isolates of rare species by modified scheme were correct. Nine isolates (1.0 %) were not identifiable by the modified scheme.
CONCLUSIONS
The modified minimal identification scheme which included MGP test identified most E. faecalis isolates rapidly and accurately. Most of E. faecium isolates were identified with the additional secondary tests. In conclusion, the system is useful for the identification of commonly isolated species of enterococci.