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Infection and Immunity, March 1999, p. 1213-1219, Vol. 67, No. 3
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Isolation and Chemical Characterization of a Capsular Polysaccharide Antigen Shared by Clinical Isolates of Enterococcus faecalis and Vancomycin-Resistant Enterococcus faecium

Johannes Huebner,1,2 Ying Wang,1 Wolfgang A. Krueger,1 Lawrence C. Madoff,1 Gayane Martirosian,1,dagger Saskia Boisot,1,Dagger Donald A. Goldmann,2 Dennis L. Kasper,1 Arthur O. Tzianabos,1 and Gerald B. Pier1,*

Channing Laboratory, Department of Medicine, Brigham and Women's Hospital,1 and Department of Medicine, Children's Hospital,2 Harvard Medical School, Boston, Massachusetts 02115-5899

Received 29 September 1998/Returned for modification 2 December 1998/Accepted 24 December 1998

Enterococci are a common cause of serious infections, especially in newborns, severely immunocompromised patients, and patients requiring intensive care. To characterize enterococcal surface antigens that are targets of opsonic antibodies, rabbits were immunized with various gentamicin-killed Enterococcus faecalis strains, and immune sera were tested in an opsonophagocytic assay against a selection of clinical isolates. Serum raised against one strain killed the homologous strain (12030) at a dilution of 1:5,120 and mediated opsonic killing of 33% of all strains tested. In addition, this serum killed two (28%) of seven vancomycin-resistant Enterococcus faecium strains. Adsorption of sera with the homologous strain eliminated killing activity. The adsorbing antigens were resistant to treatment with proteinase K and to boiling for 1 h, but were susceptible to treatment with sodium periodate, indicating that the antigen inducing opsonic activity is a polysaccharide. Antibodies in immune rabbit sera reacted with a capsule-like structure visualized by electron microscopy both on the homologous E. faecalis strain and on a vancomycin-resistant E. faecium strain. The capsular polysaccharides from E. faecalis 12030 and E. faecium 838970 were purified, and chemical and structural analyses indicated they were identical glycerol teichoic acid-like molecules with a carbohydrate backbone structure of 6-alpha -D-glucose-1-2 glycerol-3-PO4 with substitution on carbon 2 of the glucose with an alpha -2-1-D-glucose residue. The purified antigen adsorbed opsonic killing activity from immune rabbit sera and elicited high titers of antibodies (when used to immunize rabbits) that both mediated opsonic killing of bacteria and bound to a capsule-like structure visualized by electron microscopy. These results indicate that approximately one-third of a sample of 15 E. faecalis strains and 7 vancomycin-resistant E. faecium strains possess shared capsular polysaccharides that are targets of opsonophagocytic antibodies and therefore are potential vaccine candidates.

* Corresponding author. Mailing address: Channing Laboratory, Brigham and Women's Hospital, 181 Longwood Ave., Boston, MA 02115. Phone: (617) 525-2269. Fax: (617) 731-1541. E-mail: gpier{at}channing.harvard.edu.

dagger Present address: Department of Medical Microbiology, Institute of Biostructure, Warsaw University School of Medicine, 02-004 Warsaw, Poland.

Dagger Present address: Division of Infectious Diseases, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114.

Infection and Immunity, March 1999, p. 1213-1219, Vol. 67, No. 3
0019-9567/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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