Immunochemical characterization of polysaccharide antigens from six clinical strains of Enterococci.
BACKGROUND
Enterococci have become major nosocomial pathogens due to their intrinsic and acquired resistance to a broad spectrum of antibiotics. Their increasing drug resistance prompts us to search for prominent antigens to develop vaccines against enterococci. Given the success of polysaccharide-based vaccines against various bacterial pathogens, we isolated and characterized the immunochemical properties of polysaccharide antigens from five strains of Enterococcus faecalis and one strain of vancomycin-resistant E. faecium.


RESULTS
We cultured large batches of each strain, isolated sufficient quantities of polysaccharides, analyzed their chemical structures, and compared their antigenic specificity. Three classes of polysaccharides were isolated from each strain, including a polyglucan, a teichoic acid, and a heteroglycan composed of rhamnose, glucose, galactose, mannosamine, and glucosamine. The polyglucans from all six strains are identical and appear to be dextran. Yields of the teichoic acids were generally low. The most abundant polysaccharides are the heteroglycans. The six heteroglycans are structurally different as evidenced by NMR spectroscopy. They also differ in their antigenic specificities as revealed by competitive ELISA. The heteroglycans are not immunogenic by themselves but conjugation to protein carriers significantly enhanced their ability to induce antibodies.


CONCLUSIONS
The six clinical strains of enterococci express abundant, strain-specific cell-surface heteroglycans. These polysaccharides may provide a molecular basis for serological typing of enterococcal strains and antigens for the development of vaccines against multi-drug resistant enterococci.
Hsu
Carolyn T
CT
Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA. hsutlc@gmail.com
Ganong
Amanda L
AL
Reinap
Barbara
B
Mourelatos
Zafiria
Z
Huebner
Johannes
J
Wang
Julia Y
JY
D000942:Antigens, Bacterial / Q000737:chemistry* / Q000276:immunology*; D013293:Enterococcus faecalis / Q000737:chemistry / Q000145:classification / Q000276:immunology*; D016984:Enterococcus faecium / Q000737:chemistry / Q000145:classification / Q000276:immunology*; D007120:Immunochemistry; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000276:immunology*; D011485:Protein Binding
D000942:Antigens, Bacterial; D011135:Polysaccharides, Bacterial