The effect of solar ultraviolet radiation and ambient temperature on the culturability of toxigenic and non-toxigenic Vibrio cholerae in Pretoria, South Africa

Abstract

Although solar disinfection (SODIS) is known to be one way of controlling waterborne diseases like cholera, the potential impact that this technology can have in resource poor areas is increasingly being considered as a potential component in water treatment for poor and rural communities and as a means to alleviate the burden of disease. In this study, comparative growth analysis was conducted on three Vibrio cholerae strains, two toxigenic and one non-toxigenic, to test the effect of solar ultraviolet radiation (SUVR) and ambient temperature. Culturability on solid media was used in addition to flow-cytometry to evaluate the survival and integrity of the cell membrane of these bacteria after exposure to SUVR. The season of the year played an important role in the complete inactivation of the three V. cholerae strains with autumn and summer being the most significant, requiring only 7 h of exposure to render the bacteria unculturable, due to higher SUVR levels and temperature observed in these seasons. However, the results also indicated that in winter where the levels of SUVR were comparable to those in spring the extreme variation in the daily recorded ambient temperatures [± 3°C – ± 30°C] may have contributed to the observed disinfection. Key words: Solar disinfection, solar ultraviolet radiation, Vibrio cholerae, cholera.