Title : Exploring the impact of Plectranthus amboinicus L. extracts on antioxidant system and cell membrane integrity of P. aeruginosa PA01 and S. aureus NCTC8325
Background: Medicinal plants have drawn attention due to their antibacterial properties against several disease-causing bacteria. Plectranthus amboinicus has been studied to possess various biological properties that can be explored to attain new therapeutics to combat such diseases. This study investigated the effect of Plectranthus amboinicus leaf extracts on catalase activity, reactive oxygen species and lipid peroxidation activity, cytoplasmic membrane permeability and efflux pump mechanisms in S. aureus and P. aeruginosa.
Materials and methods: The effect of P. amboinicus extracts on the catalase activity of P. aeruginosa and S. aureus was screened using 30% hydrogen peroxide. The impact of extracts on the concentration of lipid peroxidation product (malondialdehyde) was spectrophotometrically determined. The total intracellular ROS concentration after exposure to the extracts was evaluated using 2′,7′-dichlorodihydrofluorescein diacetate (H2DCFDA, which is oxidized to 2′,7′-dichlorofluorescein (DCF) by ROS. The influence of extracts on the cytoplasmic membrane permeability was spectrophotometrically determined using diSC3-5 dye. Similarly, using the Rhodamine-6-G uptake assay was used to study the effect of extracts on the efflux pumps.
Results: The catalase activity in P. aeruginosa and S. aureus decreased by 60% and 20% respectively after exposure to the extracts. The generation of ROS can cause reaction with the polyunsaturated fatty acids of lipid membranes and induce lipid peroxidation. Demonstrating this phenomenon, there was an increase in ROS activity in P. aeruginosa and S. aureus after exposure to P. amboinicus extracts. Additionally, the concentration of lipid peroxidation product (malondialdehyde) increased by 42.38% and 42.5% in P. aeruginosa and S. aureus respectively. Both P. aeruginosa and S. aureus cells showed alteration in cytoplasmic permeability after treatment with P. amboinicus extracts. The extracts altered the permeability of P. aeruginosa by 58% and S. aureus by 83%. The efflux pump mechanisms were investigated using Rhodamine-6-uptake assay and displayed decrease in efflux by 25.5% in P. aeruginosa and 24.2% in S. aureus after treatment with extracts.
Conclusion: The combination of different techniques in association with the bacterial virulence factors offers additional value in understanding the influence of P. amboinicus extracts on P. aeruginosa and S. aureus.