Synergistic effect of light, pH and Artemisia annua extract on Enterococcus faecalis in aquatic microcosms

International audience; Synergistic effect of abiotic and biotic factors is not completely established in the process of disinfecting water by plant extracts. The present study aims to evaluate the synergistic effect of different pH values (4, 5, 6, 7, 8 and 9) and different infusion concentrations (10, 20 and 30%) of Artemisia annua on Enterococcus faecalis growth in aquatic microcosm under dark and lighting conditions. The results showed that under dark condition, there was a relative increase in abundance of E. faecalis cells in the presence of A. annua extract. Under lighting, there is a decrease in the abundance of E. faecalis at different infusion concentrations of A. annua. Extract of A. annua seems to favour the growth of E. faecalis cells in the dark, especially at slightly acidic pH. This growth was relatively significant at pH 6. In the presence of light, A. annua extract inhibited the growth of E. faecalis cells and this varied from one extract sample to another; and was significant at slightly basic pH. Under the lighting, different pH values do not appear to have significant influence on the inhibition of bacterial growth except for pH 8. Monoterpenes, sesquiterpenes and triterpenes molecules present in infusions could be involved in chemical reactions responsible for cellular inhibition under light condition. Research on photosensitizing compounds and a comparative study with conventional photosensitizers might attest for the involvement of photosensitivity reaction with the A. annua extracts.