The antimicrobial and immunomodulatory effects of Cotyledon Orbiculata extracts

Abstract

The challenge of antimicrobial resistance has increased drastically over the years as more microorganisms are becoming resistant to the available conventional treatments. The burden of antimicrobial resistant infections is intensified by the increase in immunocompromising conditions such as HIV/AIDS and cancer. Due to this challenge, pharmaceutical companies, health sectors and researches are in search of new antimicrobial agents that can solve the problem at hand. Medicinal plants are a reliable source for drug discovery as it is estimated that 25% of modern medicine originated from plants. They have also been used traditionally as sources of medicine in the treatment of many human ailments. Plants can also be applied in the field of nanotechnology. Nanotechnology is a promising field in medicine as it has the potential to offer improved methods for disease diagnostics and therapeutics. The use of plants in nanotechnology brings about biologically friendly nanomaterials. Cotyledon orbiculata is one of the well-known and common plants of South Africa that is used in traditional medicinal practices. The nanotechnology applications as well as the antimicrobial and immunomodulatory effects of this plant were evaluated. The ability of C. orbiculata to synthesize silver nanoparticles was determined. Optimisation of silver nanoparticle synthesis using water extract of C. orbiculata was done at different conditions. The conditions evaluated include, reaction temperature (25 and 70°C), silver nitrate concentration (1 and 3mM), plant extract concentration (1.5, 3 and 6mg/ml) and reaction time. The synthesis of silver nanoparticles using this plant was successful. The optimal conditions for the synthesis of silver nanoparticles using C. orbiculata were 3mg/ml of the C. orbiculata extract, 3mM silver nitrate at a reaction temperature of 70°C for 2 hours. Under these conditions, spherical, crystalline nanoparticles with sizes of 20-40nm were produced. The antimicrobial and immunomodulatory properties of C. orbiculata extracts and silver nanoparticles were evaluated. Antimicrobial activity was evaluated against Staphylococcus aureus, Staphylococcus epidermidis, Methicillin resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa and Candida albicans, using the micro-dilution assay to determine the minimum inhibitory concentration (MIC). The results obtained revealed that all extracts of C. orbiculata have antimicrobial properties against all the microorganisms tested. The MICs of the extracts ranged from 3.13 to 50mg/ml and the MBC/MFC from 6.25 to >100mg/ml. The methanol extract exhibited better antimicrobial activity in comparison to the others extracts whereas the water extract had better antifungal properties. The chloroform extract showed the lowest activity in both antibacterial and antifungal studies. Silver nanoparticles also exhibited antimicrobial activity against all the microorganisms tested. It’s MICs against these microorganisms ranged from 5–80μg/ml and MBC/MFC from 20-160μg/ml. The silver nanoparticles were highly active than the water extract against both the bacteria and the fungi. Immunomodulatory effects of the plant extracts and silver nanoparticles were determined by evaluating cytokine production using the enzyme linked immunoassay (ELISA) assay. All the extracts and silver nanoparticles of C. orbiculata were found to have anti-inflammatory properties. The water extracts showed more anti-inflammatory activity against the cytokines than the other extracts. However the silver nanoparticles were more active than the water extract. The findings from this study confirmed that C. orbiculata have antimicrobial and immunomodulatory effects. This provided scientific evidence of the traditional use of this plant in the treatment of skin infections and inflammatory conditions.