Demonstration of polysaccharide capsule in Campylobacter jejuni using electron microscopy

Recently, we reported that Campylobacter jejuni, an important gastrointesti nal pathogen, has the genetic determinants to produce a capsular polysaccha ride (Karlyshev et al., Mol. Microbiol. 35:529-541, 2000). Despite these da ta, the presence of a capsule in these bacteria has remained controversial. In this study we stain C. jejuni cells with the cationic dye Alcian blue a nd demonstrate for the first time by electron microscopy that C. jejuni cel ls produce a polysaccharide capsule that is retained in the coccoid form bu t is absent in a kpsM mutant.