Impact of solar irradiation on cholera toxin secretion by different strains of Vibrio cholerae

Abstract

Cholera toxin is the aetiological agent of cholera – a deadly waterborne disease acquired through the consumption of untreated water contaminated with CTXФ bacteriophage harbouring strains of V. cholerae. Solar disinfection is a re-emerging technique that relies on the ultraviolet component of sunlight to inactivate the growth of Vibrio cholerae in water, rendering the water microbiologically safe for consumption. However, studies have shown that DNA damaging agents, such as ultraviolet light, induce the replication of the CTXФ bacteriophage with subsequent expression of the cholera toxin. In this study we investigated the impact of solar irradiation on the secretion of cholera toxin by toxigenic strains of V. cholerae in water. The cholera toxin ELISA assay, qualitative and quantitative real-time PCR as well as growth on solid media were used to determine cholera toxin secretion, DNA integrity and growth of the bacteria after 7 h and 31 h of solar irradiation. Solar irradiation in water reduced the integrity of DNA, inactivated the growth of V. cholerae and, most importantly, prevented the secretion of detectable levels of cholera toxin. This finding is encouraging for resource-poor communities that may rely on solar disinfection to alleviate the burden of cholera-related fatalities.