Proposal of a New Scheme for the Serological Typing of Enterococcus faecalis Strains

No systematic study on serotyping of Enterococcus faecalis has been reported since 1964 when M.E. Sharpe conducted serotyping of group D streptococcus in U.K. So, we attempted to re-evaluate serotyping of E. faecalis. For this purpose, we received 42 Sharpe's strains and first examined for their biochemical characteristics as E. faecalis. Only 9 of the 42 strains were identified as E. faecalis. We raised rabbit antisera against a large number of E. faecalis strains, including the 9 Sharpe's strains, 2 strains obtained from CDC in U.S.A. and 36 strains isolated from patients hospitalized in different cities of Japan. From the results of cross-agglutination tests and absorption tests performed on these antisera using a large number of E. faecalis strains, we were able to classify 21 distinct serotype strains and to prepare 21 mono-specific typing antisera by absorption of the antisera to the type strains with appropriate cross-agglutinating strains. When 832 E. faecalis strains were serotyped with the 21 typing antisera, 638 strains (76.7%) were typable. Thus, we propose a provisional scheme of 21 distinct serovars in E. faecalis.