The aim of this study was to determine the cultivability of E. faecalis and enteropathogenic E. coli (EPEC) under different light intensities in the presence of different concentrations of mercury chloride (HgCl2) and biodegradable organic compound (BOC). Studied light intensities were 0, 500, 1000, 1500 and 2000 lux while studied HgCl2 concentrations were 0.001, 0.01, 0.1 and 1μg/L. The BOC used was glucose at concentrations of 0.001, 0.01, 0.1 and 1mg/L and at pH 7. The BOC used was glucose at concentrations of 0.001, 0.01, 0.1 and 1mg/L and at pH 7. The duration of incubation under light was 6 h. Results showed that E. faecalis and EPEC bacteria are inactivated by HgCl2 irrespective of studied concentration. The cells inhibition percentage (CIP) of E. faecalis varied from 94.46% to 99.53% at 0.001μg/L, from 94.77% to 99.55% at 0.01μg/L, from 94.92% to 99.57% at 0.1μg/L and from 96.97% to 99.77% at 1μg/L of HgCl2. For EPEC cells, the CIP fluctuated between 89.87% and 98.99%, between 90.67% and 99.14%, between 92.05% and 99.14% and 93.50% and 99.25% respectively in solutions containing 0.001, 0.01, 0.1 and 1µg/L of HgCl2. The highest abundance was observed under 1500 lux for E. faecalis and 500 lux for EPEC. Exposure to light seemed to intensify the toxic action of HgCl2 in the medium. Cells metabolism reactivations under 2000 lux for E. faecalis and 1000 lux for EPEC were nevertheless observed. The level of this photo-reactivation varies from one organism species to another. The oligotrophic nature of the medium could not allow studied the microorganisms to set up specific protection mechanism against HgCl2 and light.