[Factors influencing the capacity of cellular substrate adherence of vibrio cholerae O1 and non O1 strains]

Abstract

Bacterial adherence to eukariotic cells represents an important step of tissue colonization and is mediated by specific molecules called adhesins. Bacterial adherence to cellular substrate is a very complex process consisting in specific interactions between the surface of host cell and bacterial cell surface respectively. Adherence to cellular substrate confers selective advantages to bacterial cells, as: rapid growth rate by shorter lag period and protection against antibodies and lysozime. Adherence and colonization of small bowel represent the early steps of cholera infection (1, 2). The purposes of this study were to characterize the adherence ability of 46 Vibrio cholerae O1 and non O1 strains with different sources of isolation (acute diarrhea, water sources) to HEp-2 cell; to determine the influence of different factors (culture media, bacterial culture growth phase, proteolytic enzymes, carbohydrates and polyvalent agglutinant anti V. cholerae O1 serum) on the bacterial adherence capacity. Adherence capacity was assayed using the qualitative Cravioto's method. The adherence ability was appreciated by semi quantitative ("+", "++" and "+++") and quantitative assays. The adherence pattern of the tested strains was predominantly a diffuse one. The agar medium proved to be the most appropriate for the early and maximal expression of adhesion molecules, by comparison with nutritive broth and alkaline peptone water. Manose in different concentrations (1% and 3%) inhibited the adherence ability, demonstrating the role of manose-sensitive haemagglutinating fimbriae (MSHA) in mediating the adherence of V. cholerae strains to cellular substrate. Trypsine has no notable effect on the adherence ability, suggesting that the major V. cholerae adhesion molecules are not essentially of protein nature, so that the afimbrial adhesins could also play an important role in bacterial adhesion to eukariotic cells. The agglutinant polyvalent anti-V. cholerae O1 serum had the most significant inhibitory effect on the adherence ability, which was completely abolished in the presence of sub-agglutinant dilutions of serum titer (1/60-1/120) and partially reduced at titers ranging from 1/240 to 1/920. This inhibitory effect could be explained by bacterial agglutination, but also by the specific blocking of some surface structure implicated in the adherence process (i.e. lipopolysaccharides, as demonstrated by the inhibitory effect of sub-agglutinant serum titers). The inhibitory effect of polyvalent anti-V. cholerae O1 serum was limited to O1, but was not evident for the non O1 serogroups, demonstrating that the serum antibodies are acting on serogroup specific antigenic fractions.