Biochemical characteristics and antimicrobial potential of seed and nut oils against Staphylococcus aureus

Yangomodou, OD

Abstract

The antibacterial activities of oils and extracts from walnut, cashew and pumpkin were investigated on methicillin resistant and susceptible strain MRSA 252 and S. aureus ATCC 6538 using the disc agar diffusion technique. Results revealed that the tested bacteria were sensitive to the three oils. Walnut and pumpkin oil showed better activity with clear zones of inhibitions. A combinational study of oils with conventional antibiotics shows that MRSA 252 and ATCC 6538 exhibited different reactions such as synergy, resistant, potentiation and indifference effects when combined with the oils. Minimum inhibitory concentration (MIC) and minimum biofilm inhibition concentration (MBIC) tests show that inhibitory effect of walnut oil against MRSA 252 and S. aureus ATCC 6538 biofilm formation was stronger compared to cashew and pumpkin oils. In addition, minimum biofilm eradication concentration (MBEC) test revealed that walnut and pumpkin oils were able to eradicate preformed biofilms of MRSA 252 and ATCC 6538 within 48 h of growth with eradication from 12 h with reduced viable counts. Preliminary investigation of the pathogenicity of the S. aureus strains showed that MRSA 252 biofilms were more virulent against Galleria mellonella than S. aureus ATCC 6538 biofilms. A test to determine whether walnut oil could treat infections caused by both strains shows that G. mellonella previously infected with MRSA 252 and S. aureus ATCC 6538 biofilms were able to survive in a 5-day study even though they developed brownish pellicles. Scanning electron microscopy (SEM) of S. aureus biofilms shows that MRSA 252 and ATCC 6538 biofilms produced different morphological structures and slime confirming the complexity of the biofilms. Using molecular methods, polymerase chain reaction (PCR) confirms the presence of numerous virulence genes such as adhesion, biofilm and antibiotic resistance genes in MRSA 252 and ATCC 6538, gene expression analysis results indicates that intercellular adhesion (icaADBC) genes were down-regulated between 6-12 h and only upregulated at 24 h, the biofilm formation genes were up-regulated at 12, 24 and 48 h while the accessory regulatory gene (agrA) and methicillin resistant (mecA) gene were up-regulated at 12 and 24 h but down-regulated at 48 h in the strains. Preliminary chemical investigation of walnut oil indicates the presence of different compounds that could be responsible for its antimicrobial activity. Using gas chromatography–mass spectrometry (GC-MS), major and minor fatty acids were identified in walnut oil. Structural elucidation of the fractionated walnut oil sample conducted using hydrogen proton NMR ( 1H NMR), 13C NMR, attached proton test (APT), confirmed linolenic acid and glyceric acid as the probable compounds responsible for its activity against MRSA 252 and S. aureus ATCC 6538 biofilms.

Citation

Yangomodou, O. (in press). Biochemical characteristics and antimicrobial potential of seed and nut oils against Staphylococcus aureus. (Thesis). University of Salford

• Thesis Type: Thesis
• Acceptance Date: Apr 30, 2019
• Deposit Date: May 8, 2019
• Publicly Available Date: May 8, 2019
• Additional Information: Funders : Olabisi Onabanjo University (TeTFund); Projects : Biochemical Characteristics and Antimicrobial Potential of Seed and Nut Oils Against Staphylococcus aureus