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Article Title

Effects of salinity and pH on the adherence and virulence of Vibrio cholerae O139

Abstract

Vibrio cholerae must first adhere to and colonize the human small intestine in order to cause cholera and this adherence can be affected by several physicochemical factors. The purpose of this study was to examine the adherence and virulence of V. cholerae O139 that was grown in experimental broth media with different salinities and pH values. After the bacterial cells were incubated separately in these media, the adherence of V. cholerae O139 to HeLa cells was examined. By comparison with bacteria grown in a control medium with 0.5% NaCl and pH 7.0, the percentages of adhesion of bacteria grown in media with 0% and 5% NaCl were found to decline significantly by 56% (P = 0.0007) and 69% (P = 0.0008) respectively, and those in media with pH 6 and 5.5 decreased to 91% (P = 0.016) and 82% (P = 0.006) respectively. After the bacterial cells were sub-cultured in the experimental media serially, no difference in adherence was observed between the first, the fifth and the tenth generations (P = 0.182). However, after the tenth generation, when the treated bacterial cells were re-incubated in a control medium, the level of adherence was found to become similar to that of the control bacteria. In order to determine the effect of adherence on the pathogenicity of V. cholerae O139, mice were challenged with a double dose of the LD50 of the test strains incubated in 0% NaCl, 5% NaCl, and pH 5.5, and the survival of rates were at 50%, 60% and 20%, respectively. These results suggest that changes of salinity can cause a reversible inhibition effect on either adhesion or virulence of V. cholerae O139, and those effects resulting from changes in salinity are stronger than those of different pH values.

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