Research Summary: Serodiversity of Opsonic Antibodies against Enterococcus faecalis —Glycans of the Cell Wall Revisited

ABSTRACT

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.

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Publisher: Public Library of Science

Date Published: 18-March-2011

Author(s): Theilacker C., Kaczyński Z., Kropec A., Sava I., Ye L., Bychowska A., Holst O., Huebner J.

Link: https://doi.org/10.1371/journal.pone.0017839

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