Abstract

Cholera is a diarrhoeal disease caused by Vibrio cholerae O1 or O139, synonym Bengal. The main differences between V. cholerae O139 and O1 are that the former possesses a capsular polysaccharide and a different lipopolysaccharide. Transmission electron microscopy (TEM) observations of ultrathin sections of cells stained with polycationic ferritin have been used to reveal the presence of capsule on V. cholerae O139. Considering that V. cholerae O139 strain CRC266 is intended to be used as the initial progenitor for constructing an oral vaccine candidate against cholera, the main purposes of this work were: (1) evaluate the use of ruthenium red staining to visualize the capsular material of V. cholerae O139 strains, (2) compare the results with those of polycationic ferritin staining and (3) analyze relevant phenotypic characteristics, including the expression of capsular antigen in V. cholerae O139 CRC266 strain. Control strains (O1 and O139 serogroups) were exposed to polycationic ferritin and ruthenium red, and CRC266 strain was stained only with ruthenium red. TEM of ultrathin sections of ruthenium red-stained bacterial cells revealed the presence of a dense capsular material surrounding cells of V. cholerae O139 strains. However, no such material was seen in O1 strain (negative control). The results obtained with ruthenium red staining correlate with those of polycationic ferritin. TEM demonstrated the usefulness of ruthenium red staining to study the presence of capsule in V. cholerae O139 strains. Characterization of CRC266 showed that it is a rodshaped flagellated bacterium which produces both TCP and MSHA pili, as well as a thin capsule.