Dental caries remains a major health issue and the Gram-positive bacterium Streptococcus mutans is considered as the major pathogen causing caries. More recently, S. mutans has been recognised as a cause of endocarditis, ulcerative colitis and fatty acid liver disease along with the likelihood of increased cerebral hemorrhage following a stroke if S. mutans is present systemically. We initiated this study to examine the vaccine candidacy of the serotype specific polysaccharides elaborated by S. mutans. We have confirmed the carbohydrate structures for the serotype specific rhamnan containing polysaccharides from serotypes c, f and k. We have prepared glycoconjugate vaccines using the rhamnan containing polymers from serotypes f and k and immunised mice and rabbits. We consistently obtained a robust immune response to the glycoconjugates with cross-reactivity consistent with the structural similarities of the polymers from the different serotypes. We developed an opsonophagocytic assay which illustrated the ability of the post-immune sera to facilitate opsonophagocytic killing of the homologous and heterologous serotypes at titers consistent with the structural homologies. We conclude that glycoconjugates of the rhamnan polymers of S. mutans are a potential vaccine candidate to target dental caries and other sequelae following the escape of S. mutans from the oral cavity.

conjugate vaccine, rhamnan, Serotype polysaccharide, Streptococcus mutans

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
2	aLRhap	102.6	70.9	78.5	72.7	70.3	17.7
3	aDGalp	96.8	69.0	70.3	70.2	71.7	61.9
	aLRhap	101.9	74.7	76.0	71.7	70.4	18.0


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
2	aLRhap	5.12	4.17	3.88	3.57	3.76	1.29
3	aDGalp	5.13	3.89	3.92	4.02	4.20	3.74-3.74
	aLRhap	5.21	4.30	4.01	3.65	3.88	1.36


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
2	aLRhap	102.6/5.12	70.9/4.17	78.5/3.88	72.7/3.57	70.3/3.76	17.7/1.29
3	aDGalp	96.8/5.13	69.0/3.89	70.3/3.92	70.2/4.02	71.7/4.20	61.9/3.74-3.74
	aLRhap	101.9/5.21	74.7/4.30	76.0/4.01	71.7/3.65	70.4/3.88	18.0/1.36

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

454.425 g/mol (C₁₈H₃₀R₂O₁₃, R = next and previous repeats, not counted in mol weight)