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Structural and Biological Characterization of a Capsular Polysaccharide Produced by Staphylococcus haemolyticus

Sigrid Flahaut,^1, Evgeny Vinogradov,² Kathryn A. Kelley,¹ Shannon Brennan,¹ Keiichi Hiramatsu,³ and Jean C. Lee^1*

Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115,¹ Institute for Biological Sciences, National Research Council, Ottawa, Ontario, Canada K1A 0R6,² Department of Microbiology and Infection Control Science, Juntendo University, Tokyo 113-8421, Japan³

Received 11 October 2007/ Accepted 17 December 2007

The DNA sequence of the genome of Staphylococcus haemolyticus JCSC1435 revealed a putative capsule operon composed of 13 genes in tandem. The first seven genes (capABCDEFG_Sh) showed 57% similarity with the Staphylococcus aureus cap5 or cap8 locus. However, the capHIJKLM_Sh genes are unique to S. haemolyticus and include genes encoding a putative flippase, an aminotransferase, two glycosyltransferases, and a transcriptional regulator. Capsule-like material was readily apparent by immunoelectron microscopy on bacteria harvested in the postexponential phase of growth. Electron micrographs of a JCSC1435 mutant with a deleted cap region lacked the capsule-like material. Both strains produced small amounts of surface-associated material that reacted with antibodies to polyglutamic acid. S. haemolyticus cap genes were amplified from four of seven clinical isolates of S. haemolyticus from humans, and three of these strains produced a serologically cross-reactive capsular polysaccharide. In vitro assays demonstrated that the acapsular mutant strain showed greater biofilm formation but was more susceptible to complement-mediated opsonophagocytic killing than the parent strain. Structural characterization of capsule purified from S. haemolyticus strain JCSC1435 showed a trisaccharide repeating unit: –3--L-FucNAc-3-(2-NAc-4-N-Asp-2,4,6-trideoxy-β-D-Glc)-4--D-GlcNAc-. This structure is unique among staphylococcal polysaccharides in that its composition includes a trideoxy sugar residue with aspartic acid as an N-acyl substituent.

Published ahead of print on 28 December 2007.

Present address: LBCM/LR2B, Université du Littoral-Côte d'Opale, BP120, 62 327 Boulogne/mer cedex, France.