The Ethanolic Leaf Extracts of Dissotis multiflora (Sm) Triana and Paullinia pinnata Linn Exert Inhibitory Effect on Escherichia coli Through Membrane Permeabilization, Loss of Intracellular Material, and DNA Fragmentation

Background: Dissotis multiflora (Sm) Triana and Paullinia pinnata Linn are widely used in Cameroonian traditional medicine to treat infectious diseases. These plants were found to be a reservoir of antioxidant and antimicrobial agents and have the potential to be used in clinic. Objective: To determine the mechanism of action of the ethanolic leaves extracts of Dissotis multiflora and Paullinia pinnata on Escherichia coli. Methodology: The microbroth dilution method was used to determine the minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) of D. multiflora and P. pinnata ethanolic leaves extracts. The above samples were tested for their rate of killing of E. coli cells at 1 MIC and 2 MICs. Sorbitol protection, outer membrane permeability, loss of 260-nm-absorbing material, fluorescence microscopy, and DNA degradation assay were used to examine the ultrastructural changes in bacteria induced by the extracts. Results: D. multiflora and P. pinnata extracts inhibited bacterial growth with MICs of 390.62 and 781.25 µg/mL respectively, while the MBCs values were found to be 781.25 and 1562.5 µg/mL respectively. Treatment with extracts had shorter kill-time in a time-dependent manner with effect most pronounced at 2 MICs than 1 MIC. The MIC of D. multiflora increased 4x from 390.62 µg/mL after 24 h of incubation to 1562.5 µg/mL after 7 days in the presence of an osmoprotectant indicating the inhibition of synthesis of cell wall constituents. P. pinnata had no effect on cell wall. Both extracts exhibited the greatest leakage and release of DNA materials at 30, 60, 90, and 120 min in concentration-dependent manner. Treated groups had higher values than control. At low concentrations (1/2 MIC and 1 MIC), these extracts effectively permeate the intact outer membrane of Gram-negative bacteria. Both extract were implicated in DNA fragmentation. Moreover, fluorescent cells observed further confirmed its inhibitory effect against the tested pathogen. The antibacterial action involved disruption of membrane potential, increase of membrane permeabilization, leakage of cellular material, and death suggesting them to be an alternative to antibiotics. Conclusion: These findings contribute to the understanding of the antibacterial inhibitory effect of D. multiflora and P. pinnata.