Cultivability of Escherichia coli and Staphylococcus aureus in the presence of hydroethanolic extracts of Lantana camara stems and leaves: Importance of bioactive compounds in the cellular inhibition process

The presence of pathogenic micro-organisms in drinking water is responsible for certain public health diseases. The use of plant extracts is an alternative to commonly used chemical and physical treatments. The aim of this study is to evaluate the hydroethanolic extracts of Lantana camara stems and leaves on the cultivability of planktonic bacteria Escherichia coli and Staphylococcus aureus in an aquatic microcosm, to determine the effect of extract concentration (0,5 g/L, 1 g/L, 1,5 g/L and 2 g /L), incubation temperature (7 and 37 °C) and incubation time (3, 6 and 9 hours) on the cultivability of bacterial cells and also to evaluate the effect of some bioactive compounds isolated from these bacteria. The bioactive compounds identified are Stigmasterol (sterol), lantanilic acid and lantic acid (triterpenes) isolated in the leaf extract of L. camara and β-sistosterol (sterol) and oleanolic acid (triterpenes) isolated in the stem extract of L. camara . The cultivability of two bacterial strains studied is influenced by the presence of Lantana camara extract solution. A reduction in cell density was observed in the presence of the plant extract in question. With Lantana camara leaf extract, at an incubation temperature of 37 °C, the percentage of inhibition ranged from 3–100% for E. coli with the highest value observed after 6 hours at extract concentrations of 1.5 g/L and 2 g/L. In general, the extract has both a bactericidal and bacteriostatic effect on each bacterium, depending on the type of organ, whereas the effect of the bleach is specific to each bacterium. It should be noted that in the presence of E. coli , the MICs were 0.00048 mg/mL with the leaf extract and 0.0078 mg/mL with the stem extract. For this bacterium, the MBCs were 0.0039 mg/mL and 0.0312 mg/mL with the leaf and stem extracts respectively. For S. aureus , the MICs were 0.0156 mg/mL with the leaf extract and 0.0078 mg/mL with the stem extract and the MBCs were 0.0019 mg/mL and 0.0156 mg/mL (leaf and stem, respectively). The CMB/MIC ratio shows a bactericidal effect at the level of β-sistosterol in E. coli . On the other hand, in S. aureus , this report shows a bacteriostatic effect and tolerance with the two isolated chemical compounds. The Kruskal-Wallis test shows that the abundance of cultivable cells of each bacterial species differed significantly from one incubation temperature to another at each extract concentration and at each incubation temperature for each part of the plant (P<0.05). The data obtained from this exploratory study makes it possible to consider the use of Lantana camara hydroethanolic extract as an alternative method in water disinfection.