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Chapter 28 : Campylobacter jejuni Capsular Polysaccharide
Category: Bacterial Pathogenesis
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This chapter provides a review of the biochemistry, genetics, and biological roles of Campylobacter capsular polysaccharides (CPSs). The chapter is limited to consideration of PS capsules that have been detected in Campylobacter jejuni and other closely related species such as Campylobacter coli. Differentiation between groups is not based on antigenic or structural differences of the polysaccharide (PS) chains, but on such features as the mechanisms of biosynthesis, assembly, genetic regulation, and sequence similarity. The first indirect evidence of CPS produced by C. jejuni was reported. The first one to be studied was the kpsM mutant of strain NCTC 11168. Importantly, the absence or presence of these modifying groups affects the stainability of the PSs with silver and/or its interaction with homologous antiserum, which may in part explain their previous lack of detection in some serotypes. Differentiation of CPS-producing strains could be based on the probes corresponding to the genes involved in particular biosynthetic pathways. It would also be interesting to study a role of phosphoramidate modification of CPS in colonization and interaction with the host immune system. Initial attempts to develop a vaccine against C. jejuni infection, particularly in chickens, have not been very successful. Initial studies in the development of a human vaccine have focused on the use of heat- and formalin-attenuated whole-cell vaccines. In another study, a live attenuated Salmonella strain vectoring the PEB1 antigen of C. jejuni, which is implicated in colonization ability was evaluated as a vaccine against Campylobacter infection, but no protection was observed.
Organization of gene clusters involved in the biosynthesis of enterobacterial groups II and III and Campylobacter jejuni CPSs. Open block arrows, kpsM/T genes encoding ABC transporter; solid block arrows, other genes involved in CPS transport and assembly; thin arrow, direction of transcription of the genes in the internal biosynthetic region (region 2 genes according to Whitfield, 2006 ).
Gene cassettes involved in Hep biosynthesis and correlation between gene dmhA (open arrows) and the presence of a deoxy form of Hep in the C. jejuni CPS repeating unit. Strains RM1221 (HS:53) ( Gilbert et al., 2007 ; Parker et al., 2006 ), 81-176 (HS:23/36) ( Karlyshev et al., 2005 ), and CG8486 (HS:4) ( Poly et al., 2007 ). Solid arrows, other Hep-related genes; white arrows, other genes.
CPS structures of C. jejuni. HS:1 ( McNally et al., 2005 ), HS:2, ( Karlyshev et al., 2005 ; McNally et al., 2007 ), HS: 3 ( Aspinall et al., 1995 ), HS:6, ( Muldoon et al., 2002 ), HS:19 ( McNally et al., 2006 ), HS:23/36 ( Aspinall et al., 1992 ), and HS:53 ( Gilbert et al., 2007 ). Some side chain groups may be absent as a result of structural variation. Fru, fructose, Hep, heptose, Gal, galactose; Glc, glucose; GlcA, glucuronic acid; Gro, glycerol; Man, mannose; Rib, ribose; NGro, aminoglycerol; NEtn, ethanolamine; MeOPN, O-methyl phosphoramidate. Furanose and pyranose configurations of sugars are denoted by letters f and p, respectively.
(A) Structure of Alcian blue dye (http://en.wikipedia.org/wiki/Image:AlcianBlue.png#file). (B) Electrophoretic detection of a lipid-free form of CPS from strain G1(HS:2) released after hydrolysis with a mixture of phospholipases D and A2 ( Karlyshev and Wren, 2001 ); lane 1, native CPS; lane 2, lipid-free form of CPS; lane 3, LPS of S. enterica serovar Typhimurium; lane 4, protein size markers. CPS, capsular polysaccharide; CPS-PL, lipid-free form of CPS; LOS, lipooligosaccharide.
Mechanism of release of a lipid-free form of CPS by phospholipases. The structure of the CPS lipid anchor determined for strain 81-176 ( Corcoran et al., 2006 ) with predicted cleavage sites by phospholipases A2 and D (according to Ghannoum et al., 2000 ). X, polysaccharide moiety.
Detection of capsule from C. jejuni G1 (HS:2) by electron microscopy ( Karlyshev et al., 2001 ).