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

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

^* To whom correspondence should be addressed. Email: jclee{at}rics.bwh.harvard.edu.

	Abstract

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 (cap_ShABCDEFG) showed 57% similarity with the S. aureus cap5(8) locus. However, the cap_ShHIJKLM genes are unique to S. haemolyticus and include genes encoding a putative flippase, an aminotransferase, two glycosyl transferases, and a transcriptional regulator. Capsule-like material was readily apparent by immmunoelectron microscopy on bacteria harvested in the post-exponential 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 poly-glutamic 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 showed that the acapsular mutant strain showed greater biofilm formation but was more susceptible to complement-mediated opsonophagocytic killing compared to 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--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.