Abstract
Capnocytophaga canimorsus is a dog’s and cat’s oral commensal which can cause fatal human infections upon bites or scratches. Infections mainly start with flu-like symptoms but can rapidly evolve in fatal septicaemia with a mortality as high as 40%. Here we present the discovery of a polysaccharide capsule (CPS) at the surface of C. canimorsus 5 (Cc5), a strain isolated from a fulminant septicaemia. We provide genetic and chemical data showing that this capsule is related to the lipooligosaccharide (LOS) and probably composed of the same polysaccharide units. A CPS was also found in nine out of nine other strains of C. canimorsus. In addition, the genomes of three of these strains, sequenced previously, contain genes similar to those encoding CPS biosynthesis in Cc5. Thus, the presence of a CPS is likely to be a common property of C. canimorsus. The CPS and not the LOS confers protection against the bactericidal effect of human serum and phagocytosis by macrophages. An antiserum raised against the capsule increased the killing of C. canimorsus by human serum thus showing that anti-capsule antibodies have a protective role. These findings provide a new major element in the understanding of the pathogenesis of C. canimorsus.
Highlights
Capnocytophaga canimorsus are capnophilic Gram-negative bacteria that belong to the family of Flavobacteriaceae in the phylum Bacteroidetes
Most of the work was done with strain C. canimorsus 5 (Cc5), we show that the presence of a capsule is most likely a commonality in C. canimorsus
We provide genetic and analytical data showing that the capsular polysaccharides (CPS) and LOS O-antigen repeating units share similar monosaccharides and epitopes
Summary
Capnocytophaga canimorsus (formerly Centers for Disease Control group DF-2) are capnophilic Gram-negative bacteria that belong to the family of Flavobacteriaceae in the phylum Bacteroidetes. We show that C. canimorsus 5 possesses a lipooligosaccharide (LOS) rather than a LPS and a capsular polysaccharide (CPS) likely made of the same O-antigen repeating units.
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