Survival of enteric bacteria in relation to simulated solar radiation and other environmental factors in marine waters

The survival rates of enteric bacteria (i.e. Escherichia coli and enterococci) exposed to a sunlight simulator were determined at two different depths of sea water in varying conditions of light intensity, turbidity, sewage content, degree of mixing and temperature under controlled laboratory conditions. The combined effect of these factors on bacterial die-off was evaluated by statistical analyses carried out on the experimental data obtained according to the central composite experimental design. The magnitude and the general character of the influence of the factors were determined. The variability of bacterial mortality due to the effect of light was shown to depend on the variability of the intensity of light and the other microenvironmental factors (i.e. turbidity, sewage content, and mixing) influencing the depth profile of the light intensity and bacterial concentration. All factors except temperature were found to exert a significant influence on bacterial die-off under light conditions. Higher rates of die-off were brought about by high levels of light intensity and mixing with low levels of turbidity and sewage content of the water. No appreciable difference was found between the survival capabilities of E. coli and enterococci on exposure to light.