Synthesis, Characterization and Evaluation of Novel Treatment against Resistant Pathogenic Bacteria

Abstract

BACKGROUND: Antibiotic resistance amongst microbial pathogens has become a challenge over past decades, bringing about genuine and frequently deadly contaminations that can't be dealt with by ordinary means. This has led to a search on developing solutions to this problem by searching for new source of antimicrobial agents or chemically altering the existing ones. Traditional medicinal plants and nanoparticles are highly targeted as promising agents to address the challenge. Pyrenacantha grandiflora Baill from Icacenaceae family possess pharmaceutical activities and is used by Vhavenda people to cure gastrointestinal related infections, diarrhea and tooth pain. OBJECTIVES: The present study aimed to synthesize, characterize and evaluate the efficacy of Pyranacantha grandiflora extracts alone and when conjugated with selected nanoparticles against pathogenic microorganisms. Furthermore, this study investigated the efficacy of selected antibiotics when conjugated with nanoparticles against selected pathogenic microbes. METHODS: Pyrenacantha grandiflora Baill (tubers) were collected from Masisi area. Bioactive compounds were extracted using different solvents such as methanol, acetone, hot water, dichloromethane and chloroform. Preliminary phytochemical screening was done to identify different phytochemicals in the extracts and their functional groups were identified by Fourier Transform Infrared spectroscopy (FTIR). Extracts were further assessed for their total phenolic and flavonoids content. Thin layer chromatography was used to separate the compounds from the plant extracts and active compounds/group of compounds were identified by bioautography. The antioxidant ability of the extracts to scavenge free radical DPPH was also determined. Silver and gold nanoparticles were synthesized using chemical and biological methods, characterized by Ultraviolet-Visible Spectrophotometry (UV-VIS), Transmission Electron Microscopy (TEM) and Energy dispersive X-ray analysis (EDX). Plant extracts, nanoparticles and antibiotics were xix conjugated differently, and conjugates were analyzed by FTIR and their antimicrobial activities were evaluated against different bacteria and fungi. The conjugates were tested for antimicrobial activity against extended beta-lactamase producing Escherichia coli (ATCC 35218), Escherichia coli (ATCC 25922), methicillin-resistant Staphylococcus aureus (ATCC 25923), methicillin-susceptible Staphylococcus aureus (ATCC 33591) and beta-lactamase producing Klebsiella pneumonia (ATCC 700603) using agar diffusion assay and the minimum inhibitory concentrations (MIC) were determined using the microdilution method. The minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC) were determined by sub-culturing from the MIC plates on Mueller-Hinton Agar. RESULTS: Pyrenacantha grandiflora was found to contain phenolics, saponins, alkaloids, tannin, steroids, terpenoids and flavonoids. FTIR spectroscopic studies revealed different characteristic peak values with various functional compounds similar in most extracts but differed with transmittance values. The total phenolic contents in the examined extracts ranged from 14.167 to 19.02 mg GA/g. The total flavonoid content in the examined extracts ranged from 26.603 to 34.621 mg QE/g. Thin-layer chromatography revealed various Rf values and when analyzed with bioautography, well-defined inhibition zones within the Rf value of 0.236 was identified against E. coli and K. pneumonia. The MICs of the extracts were determined, and all the extracts showed some antimicrobial activity against all tested strains ranging from 0.06-7.5 mg ml/g. Some extracts appeared to be fungicidal and hot water extracts were more active against Cryptococcus neoformans with the MFC value of 0.06 mg/ml. The methanol extract was also active against most tested strains including Candida tropicalis with the minimum fungicidal concentration value of 3.75 mg/ml. Pyrenacantha grandiflora tuber extracts conjugated with silver or gold nanoparticles exhibited a good antibacterial activity against all bacterial strain used and very few were able to exhibit bactericidal activity. Penicillin showed improvement of antibacterial activity xx when conjugated with compounds from the acetone extracts and vancomycin was found to be more effective when conjugated with silver nanoparticles and water extracts. CONCLUSION: The present study validated the efficacy of conjugated P. grandiflora tuber extracts which is used in traditional medicine. The results revealed that water extracts which are generally used by the traditional healers are active against most microorganisms tested as well as methanol and acetone extracts and the synergistic effect was observed when they were conjugated to gold and silver nanoparticles. The results of the present investigation clearly indicate that antimicrobial activity of Pyrenacantha grandiflora Baill tuber when conjugated with selected nanoparticles and antibiotics vary with test strain and the type of solvent used during extraction, thus giving hope for future development of drug leads.