Interactive efficacies between fever-reducing plants and silver nanoparticles

Abstract

Fever is a common symptom in infectious disease and one of the compelling factors for seeking healthcare. Traditional healthcare in South Africa is still widely relied on by developing communities. A literature review reveals that numerous medicinal plants are frequently used in the treatment of fever. Additionally, nanotechnology has received widespread attention in the 21st century in various fields of research. Of particular interest in this research is their antimicrobial properties. This study is aimed to investigate the antimicrobial properties of fever- reducing medicinal plants and whether these properties may be enhanced by the formation of Silver Nanoparticles (AgNPs) capped with compounds from these extracts. A total of 80 medicinal plants (40 aqueous and 40 organic extracts) related to fever treatment were screened for their antimicrobial properties. The microdilution minimum inhibitory concentration (MIC) assay was applied and nine test pathogens were selected for further study based on their ability to cause fever through bloodstream infections (septicaemia). The lowest MIC value was displayed by the organic extracts of Eucalyptus globulus Labill. (MIC of 4.00 μg/mL) against Clostridium perfringens (ATCC 13124). High antimicrobial activity was also demonstrated by the organic extracts of Helichrysum odoratissimum (L.) Sweet against C. perfringens (MIC of 0.01 mg/mL) and Listeria monocytogenes (ATCC19111) (MIC of 0.13 mg/mL). With regards to the aqueous extracts, Gunnera perpensa L. proved to be the most active medicinal plant, displaying noteworthy activity against Klebsiella pneumoniae (ATCC 13883) (MIC of 0.5 mg/mL), Staphylococcus aureus (ATCC 25723) (MIC of 0.5 mg/mL) and against Serratia marcescens (ATCC 13880) (MIC of 0.13 mg/mL). Ten well-known medicinal plant species (aqueous extracts) were selected for the synthesis of AgNPs. The AgNPs were synthesised using a one-pot green synthesis approach. Characterisation was done using the UV-Vis spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Zeta sizer, and Transmission electron microscope (TEM). The antimicrobial properties of the AgNPs were tested using the MIC assay, against two Gram-positive and two Gram-negative pathogens. A general increase in antimicrobial properties was observed. The AgNPs of three medicinal plants demonstrated noteworthy activity against all the four pathogens tested. Gunnera perpensa demonstrated MIC values of 0.63 mg/mL against Enterococcus faecalis (ATCC 29212) and L. monocytogenes, and MIC values of 0.16 mg/mL against Acinetobacter baumannii (ATCC 19606) and K. pneumoniae. Sclerocarya birrea demonstrated MIC values of 0.31 mg/mL against E. faecalis and L. monocytogenes, MIC values of 0.16 mg/mL against A. baumannii, and 0.69 mg/mL against K. pneumoniae. Eucomis autumnalis demonstrated MIC values of 0.63 mg/mL against L. monocytogenes, A. baumannii and K. pneumoniae, and MIC values of 0.16 mg/mL against E. faecalis. The highest increase in antimicrobial activity was noted for the AgNPs of T. violacea and P. sidoides where > 100 fold increase was observed against E. faecalis and > 78.14 fold increase was observed against A. baumannii respectively. Medicinal plants that were found to have noteworthy antimicrobial activity from MIC assays, together with the synthesised AgNPs, were further screened for toxicity using the Brine Shrimp Lethality Assay (BSLA). Only 28% of the organic medicinal plants were found to be toxic to the brine shrimp, and 21% of the aqueous extracts were toxic. With regards to AgNPs toxicity screening, only the AgNPs of G. perpensa were toxic, with a percentage mortality of 56.5%. The remaining AgNPs displayed a percentage mortality less than 50%. The outcomes obtained from this study suggest that the potential of fever medicinal plants in antimicrobial studies should not be overlooked. Furthermore, it was evident that the incorporation of nanotechnology to enhance antimicrobial efficacy is a feasible avenue to explore in potentiating these extracts against bacterial infections.