Efeito da radiação solar e da salinidade sobre o crescimento de Escherichia coli

Abstract

Marine waters have a toxic effect over enteric bacteria, including Escherichia coli which is widely recognized as a microbiological indicator for fecal pollution. Several factors, such as solar radiation, salinity, pH, temperature and nutrients shortage, affect the survival of this bacterium in the marine environment. This work is aimed to study the effect of solar radiation and salinity on the survival of E. coli. An E.coli strain was isolated from a water sample taken from the outfall of a pluvial gallery, in front of the Mucuripe beach, and biochemically identified. Ten sterile transparent flasks and ten sterile amber flasks, each one containing 9 mL of marine water with salinity between 33 and 35‰ and pH between 7.23 and 7.56, were inoculated with 1 mL of the TSA-grown culture, and diluted with sterile saline until the tube reached a turbidity of 0.5 in the McFarland scale. The flasks were then subjected to 10 days of exposure to solar light, running simultaneously a control experiment following the same treatment conditions in the dark. 10 repetitions of the experiment were performed. The bacterial survival was evaluated by the Standard Plate Count assay (SPC), starting with t = 0 (the initial inoculation) and until t = 216 hours. The results showed a plate count every cloudy or rainy day of solar exposure, while in days of strong solar irradiation a significant decrease of the bacterial population was observed. During the same periods, the controls showed no significant decrease. The variance analysis (ANOVA) used to process the obtained data showed a correlation between the time of exposure to solar radiation and the decrease of E. coli cells.