**3.** *Artemisia annua* **extracts**

#### **3.1 Bioactive** *Artemisia* **compounds**

Phytochemical analysis reveals the presence of alkaloids, free flavonoids, tannins, triterpenes and sterols, anthocyanins, reducing compounds, mucilages and coumarins in the extracts of *A. annua* [24, 25].

#### **3.2 Effect of** *Artemisia annua* **leaves extract on** *Escherichia coli*

The rates of change of bacterial concentrations varied in the presence and absence of light in the different media. In the dark, the rates of change of *E. coli* cell concentrations ranged from −12 to 50 cells/h. Minimum rates were obtained in pH 4 solutions. Maximum rates were recorded in pH 9 media. Negative values were noted in the pH 4 and pH 5 solutions. These negative rates indicate a relative inhibition of cell metabolisms in the presence of the plant extracts. In the control solutions, the rates of change in cell concentrations sometimes reached −19 cells/h (**Table 2**).

In the presence of light, the evolutionary rates of cell concentrations fluctuated between −14 and − 12 cells/h. Minimum rates were obtained in solutions containing *A. annua* extract at pH 4. Maximum rates were recorded at pH 8. In the control solutions, the rates of change in cell concentrations often reached −8 cells/h (**Table 2**).

The growth of *E. coli* was favored by slightly alkaline pH in the *Artemesia annua* extract solution, when grown in dark. The secondary metabolites present in the *Artemesia annua* extract are potentially involved in the physico-chemical modifications of the medium, promoting the observed cell growth. These results suggest that the *A. annua* extract does not present a bactericidal activity in water treatment in the absence of light. The study of the impact of light on *E. coli* bacteria in the presence of *A. annua* extract leads to a significant reduction in cell densities in comparison with the evolution of cell abundances in the dark. Leaves


#### **Table 2.**

*Evolution rates of* E. coli *cell concentrations (and regression coefficient) at each pH value and experimental condition [24, 25].*

of *A. annua* contain organic and inorganic substances and bioactive compounds. Molecules from extracts of *A. annua* can be a source of nutrients in the experimental conditions and allow the growth of different species. The study of the impact of light on *E. coli* bacteria in the presence of *Artemisia annua* extract leads to a significant reduction in cell densities in comparison with the evolution of cell abundances in the dark. This inhibition is explained by the effect of photosensitive compounds originating from the extract of *A. annua*. These compounds can induce a photosensitization reaction capable of inhibiting the metabolism of *E. coli* bacterial cells, since in the absence of light, no significant inhibition is observed.
