In a typing system based on opsonic antibodies against carbohydrate antigens of the cell envelope, 60% of Enterococcus faecalis strains can be assigned to one of four serotypes (CPS-A to CPS-D). The structural basis for enterococcal serotypes, however, is still incompletely understood. Here we demonstrate that antibodies raised against lipoteichoic acid (LTA) from a CPS-A strain are opsonic to both CPS-A and CPS-B strains. LTA-specific antibodies also bind to LTA of CPS-C and CPS-D strains, but fail to opsonize them. From CPS-C and CPS-D strains resistant to opsonization by anti-LTA, we purified a novel diheteroglycan with a repeating unit of →6)-β-Galf-(1→3)-β-D-Glcp-(1→ with O-acetylation in position 5 and lactic acid substitution at position 3 of the Galf residue. The purified diheteroglycan, but not LTA absorbed opsonic antibodies from whole cell antiserum against E. faecalis type 2 (a CPS-C strain) and type 5 (CPS-D). Rabbit antiserum raised against purified diheteroglycan opsonized CPS-C and CPS-D strains and passive protection with diheteroglycan-specific antiserum reduced bacterial counts by 1.4-3.4 logs in mice infected with E. faecalis strains of the CPS-C and CPS-D serotype. Diheteroglycan-specific opsonic antibodies were absorbed by whole bacterial cells of E. faecalis FA2-2 (CPS-C) but not by its isogenic acapsular cpsI-mutant and on native PAGE purified diheteroglycan co-migrated with the gene product of the cps-locus, suggesting that it is synthesized by this locus. In summary, two polysaccharide antigens, LTA and a novel diheteroglycan, are targets of opsonic antibodies against typeable E. faecalis strains. These cell-wall associated polymers are promising candidates for active and passive vaccination and add to our armamentarium to fight this important nosocomial pathogen.

antibodies, antibody specificity, teichoic acids, Serotypes, typing, vaccination, whole cell, Enterococcus faecalis, Structural Homology

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3	l?Lac	181.29	77.72	19.21
3	bDGalf	109.26	80.26	84.96	82.41	70.55	71.90
	bDGlcp	103.22	74.05	82.44	68.8	76.26	61.26


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3	l?Lac	-	4.038	1.361
3	bDGalf	5.315	4.346	3.932	4.225	4.040	3.768-4.019
	bDGlcp	4.542	3.460	3.663	3.465	3.500	3.742-3.930


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3	l?Lac		77.72/4.038	19.21/1.361
3	bDGalf	109.26/5.315	80.26/4.346	84.96/3.932	82.41/4.225	70.55/4.040	71.90/3.768-4.019
	bDGlcp	103.22/4.542	74.05/3.460	82.44/3.663	68.8/3.465	76.26/3.500	61.26/3.742-3.930

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*OC[C@@H](O)[C@@H]1O[C@@H](O[C@@H]2[C@@H](O)[C@H](*)O[C@H](CO)[C@H]2O)[C@H](O)[C@H]1OC(C)C(=O)O

396.345 g/mol (C₁₅H₂₄R₂O₁₂, R = next and previous repeats, not counted in mol weight)