**4.2 Effect of** *Moringa oleifera* **extract on** *Escherichia coli*

The abundances of *E. coli* in different extract concentrations ranged from 500 × 103 to 0.92 × 103 CFU/100 mL. At 4°C, it ranged from 224.48 × 103 to 3.58 × 103 CFU/100 mL. The lowest abundance was recorded at 10 g/L and the highest at 1 g/L (**Figure 2**).

At 23°C, it ranged from 129.7 × 103 to 0.92 × 103 CFU/100 mL, with the lowest abundance recorded at 30 g/L and the highest at 1 g/L. The cell concentrations in the control (solution without seed extract) were 500 × 103 CFU/100 mL at 23°C and 4°C, respectively (**Figure 2**).

The obtained inhibition percentages and temporal variation of *E. coli* cell abundances show that *Moringa oleifera* seed extract can be used as a natural alternative for efficient water treatment. The antibacterial activity of *M. oleifera* seed extract is believed to be due to the presence of a cationic protein molecule present in the seed. This protein, commonly known as *M. oleifera* cationic protein (MOCP), is responsible for the death of bacterial cells by rapid flocculation and fusion of their inner and outer membranes. This protein would inhibit the growth of bacteria at higher concentrations, thus facilitating the antibacterial inhibition of the latter. However, this activity is dependent on the bacterial load, and an increased bacterial concentration would require a higher dose or higher concentration of the seed extract. The inhibitory effect of *M. oleifera* seed extract against bacterial cells is thought to be related to phytochemicals such as alkaloids, flavonoids and tannins, among others steroids, saponins, phenols, terpenoids and finally coumarins and anthraquinones present in the different seed extracts.

Temperature appears to be an important factor involved in cell inhibition by the aqueous extract of *M. oleifera* seeds. Incubation temperature increases the efficacy of the aqueous extract of *M. oleifera* seeds, with considerable inhibition at psychrophilic temperature. The seeds have been reported to contain calcium, magnesium, phosphorus, copper, vitamins (A, B and E) and are also rich in organic elements. These different secondary metabolites, sometimes present in large quantities in the extracts, could accumulate in the cell wall of *E. coli* and become toxic. The inhibition of bacteria could also be due to the presence of the isothiocyanate molecules α-L-rhamnosyloxy benzyl which are found in the seeds and whose antibacterial and *Understanding of Cultivability of* Escherichia coli *in Aquatic Microcosm in the Presence... DOI: http://dx.doi.org/10.5772/intechopen.102861*

#### **Figure 2.**

*Enteropathogenic* E. coli *(EPEC) abundance depends on the concentration of* Moringa oleifera *seeds extracts [26].*

antifungal properties have been described. These molecules are soluble and positively charged. They can easily cross the bacterial membrane to bind to negatively charged cationic proteins on the cell membrane surface and support their inhibition. Water disinfection with Moringa seeds requires relatively high doses of 200 g/L of extract to have a germicidal effect. With a variation of extract concentrations from 1 g/L to 40 g/L, the bacterial inhibitions varied from 55.12% to 99.9% for enteropathogenic *E. coli*. This suggests that the environment, as well as the genetic characteristics of the bacteria or other abiotic properties of the water used, could affect the activity of the constituents of the seeds and other parts of the plant (root barks and stems).

### **5. Conclusion**

Drinking water is often subject to bacteriological contamination, causing serious health problems due to diarrhoeal diseases, gastroenteritis, cholera and typhoid fever. In recent years, water disinfection methods using plant extracts have been proposed as a new alternative for household water treatment. Information on the conditions of the use of plant extracts in the treatment of bacterio-contaminated water is often not available. The chapter aimed to summarize the known effects of some plant extracts on the cultivability of *E. coli* cells.

The results show that the presence and absence of light determine the action of the plant extracts on the survival of *E. coli* bacteria in aquatic environments. In the absence of light, *A. annua* extracts can sometimes promote bacterial cell activity. This activity is influenced by the pH of the solutions, the sensitivity of the bacterial cells under monospecific conditions being observed. The impact of the pH would be linked to a variation of the assimilation coefficient of nutritive substances.

In the presence of light, the plant extract inactivates bacterial metabolism to varying degrees. This variability depends on the concentration of the extract. The rate of photo-oxidation reactions that lead to bacterial inactivation is pH dependent, and varies from one bacterial species to another. The presence of light increases the inhibitory effect of plant extracts on *E. coli* cells.

The use of medicinal plants in water disinfection offers many opportunities in a world where access to safe drinking water remains a permanent concern for public authorities, therefore it should be considered to use plant extracts as an alternative process for water disinfection.
