Characterization of essential oil from Ocimum gratissimum leaves: Antibacterial and mode of action against selected gastroenteritis pathogens -

Characterization of essential oil from Ocimum gratissimum leaves: Antibacterial and mode of action against selected gastroenteritis pathogens

Abstract: The research paper analyzed the essential oil of Ocimum gratissimum leaves and identified 37 compounds, with eugenol as the major component. The antimicrobial activity of the essential oil was tested against four gastroenteritis pathogens, showing antibacterial effects with minimal inhibitory concentrations (MICs) of 1-2 mg ml-1 and rapid killing effects within 5 s at four times the MIC against Escherichia coli and Salmonella Typhimurium. Various assays indicated that the essential oil increased the permeability of microbial cell membranes, leading to membrane disruption. The findings suggest that the antibacterial property of the essential oil could be due to its disruptive action on the cytoplasmic membrane of the tested microorganisms.

Introduction: The paper discusses gastroenteritis, its symptoms, and its causes, mainly by viruses, bacteria, and parasites. Diarrhea is a significant cause of death in children under 5 years old. With the decreased efficiency of antibiotic drugs due to resistant pathogens and their unwanted side effects, the need for novel antibacterial agents, especially plant-derived natural products, is emphasized. Essential oils, particularly rosemary oil, clove oil, and thyme oil, have been found to exhibit strong antibacterial and anticandidal activities. The antibacterial mechanism of essential oils is related to their ability to disrupt bacterial cell membrane and mitochondria, leading to membrane integrity breakdown. The study focuses on Ocimum gratissimum essential oil (OGEO) and its chemical compositions, antibacterial activity against four gastroenteritis pathogens, and mechanism of action against selected bacteria. The antibacterial activity and mechanism of action of OGEO were investigated through various assays, including protein leakage assay, SDS-PAGE, penetration of propidium iodide into the cells, alteration of cell membrane by SEM, and time kill assay.

Materials and methods: The methods involved harvesting O. gratissimum leaves in Thailand and extracting the essential oil through steam distillation. The chemical composition of the oil was analyzed using a gas chromatography-mass spectrometry system. The antimicrobial activity of the oil was evaluated against various bacterial strains using MIC and MBC determination, time-kill assays, and membrane damage assays. These included LIVE/DEAD BacLight assay, 260 nm absorbing material leakage assay, protein leakage assay, SDS-PAGE analysis, and SEM analysis. The essential oil showed significant antimicrobial activity and induced membrane damage in the tested bacterial strains, suggesting its potential as a natural antimicrobial agent. These findings provide valuable insights into the potential applications of O. gratissimum essential oil as an antimicrobial agent.

Results: The study extracted oil from O. gratissimum leaves and identified 37 compounds, with eugenol being the major one. The oil demonstrated antibacterial activity against tested pathogens, particularly S. flexneri, and exhibited bactericidal properties. Time-kill experiments showed significant bacterial reduction, with complete removal of pathogens at high doses within 2 hours. Fluorescence dye and UV-absorbing material release assays indicated membrane damage and cell lysis in treated bacteria, supported by protein leakage and intracellular protein release assays. Gel electrophoresis confirmed the release of intracellular proteins by treated cells. Furthermore, scanning electron microscopy showed alterations in bacterial membrane morphology, especially in gram-negative bacteria. These findings indicate the potential of O. gratissimum essential oil as an antibacterial agent, particularly against gram-negative pathogens.

Discussion: The study identified major chemical components in the essential oil of O. gratissimum, with eugenol, cis-ocimene, and sesquiterpenes being the main components. The antimiocrobial properties of O. gratissimum essential oil were explored, demonstrating efficacy against various bacteria, with eugenol being a significant contributor to this activity. Synergistic effects of essential oil components were also observed. However, some pathogenic bacteria exhibited high resistance to essential oils. Time-kill assays showed rapid bactericidal activity of O. gratissimum essential oil. The mode of action of the oil against bacteria involved membrane disruption, leading to increased membrane permeability, leakage of intracellular materials, and eventual cell death. SEM analysis further confirmed the structural changes and damage to bacterial cells caused by the essential oil. These findings provide insights into the potential use of O. gratissimum essential oil as an antimicrobial agent, particularly in the context of combating bacterial resistance and rapid bactericidal activity.

Conclusion: The research investigated the chemical composition of essential oil derived from O. gratissimum in Thailand, identifying eugenol, Z-ocimene, and γ-muurolene as main components. The essential oil demonstrated strong antimicrobial activity against four gastroenteritis pathogens, with rapid bactericidal action and a primary mode of action involving disruption of the bacterial cell membrane, increasing its non-specific permeability. This action led to leakage of intracellular constituents and ultimately cell death. The study suggests that essential oil of O. gratissimum may be an attractive antibacterial agent against gastroenteritis bacteria, as agents targeting bacterial membrane disruption may be less likely to induce drug resistance compared to antibiotics targeting other bacterial systems.

Reference:-

CHIMNOI, N., REUK-NGAM, N., CHUYSINUAN, P., KHLAYCHAN, P., KHUNNAWUTMANOTHAM, N., CHOKCHAICHAMNANKIT, D., THAMNIYOM, W., KLAYRAUNG, S., MAHIDOL, C. AND TECHASAKUL, S., 2018. Characterization of essential oil from Ocimum gratissimum leaves: Antibacterial and mode of action against selected gastroenteritis pathogens. Microbial Pathogenesis, 118, pp.290-300.