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 monospecific 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.

The rate of isolation of Enterococcus faecalis as the causative bacterium of complicated urinary tract infections has been increasing. However, the pathogenicity of this bacterium in the urinary tract has not been clarified. Thus, the authors investigated how E. faecalis is pathogenic to the urinary tract, using mice with experimental urinary tract infection. The investigation revealed that this bacterium when sufficiently numerous can be directly pathogenic. The bacterium can be pathogenic indirectly when present with other typical urinary bacteria such as E. coli.

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Using a mouse experimental UTI (urinary tract infection) model , a study was conducted to find the pathogenicity of various serovars of E. faecalis. On the basis of studies employing serovar-specific factor sera prepared with E. faecalis type strains, serovar 2, 3, 4 and 10 strains showed a high incidence of involvement in pyelonephritis: 90 .3%, 85.7%, 85% and 73.3%. Serovar 1, 6 and 7 strains each showed a 63.6% incidence of involvement in pyelonephritis , indicating that they have a moderate pathogenicity. The pathogenicity of the other serovar strains was not very strong, with a low incidence of 40-59 .1%. These results were thus in good agreement with the findings of the study using the mouse experimental UTI model infected with clinical isolates. Serotyping was performed of E. faecalis clinical isolates obtained from patients with pyelonephritis or urosepsis. Serovars 2 and 4 comprised 75.1% of those isolates. It was surmised that E. faecalis serovars 2 and 4 tend to have strong pathogenicity. Thus, there were quite a few differences in pathogenicity of E. faecalis according to each kind of serovar.