Differential Antimicrobial Effect of Essential Oils and Their Main Components: Insights Based on the Cell Membrane and External Structure

Abstract

The biological activity of essential oils and their major components is well documented. Essential oils such as oregano and cinnamon are known for their effect against bacteria, fungi, and even viruses. The mechanism of action is proposed to be related to membrane and external cell structures, including cell walls. This study aimed to evaluate the biological activity of seven essential oils and eight of their major components against Gram-negative and Gram-positive bacteria, filamentous fungi, and protozoans. The antimicrobial activity was evaluated by determination of the Minimal Inhibitory Concentration for Bacillus cereus, Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, Salmonella Typhimurium, Shigella sonnei, Aspergillus niger, Aspergillus ochraceus, Alternaria alternata, and Fusarium oxysporium, the half-maximal inhibitory concentration (IC50) for Trypanosoma cruzi and Leishmania mexicana, and the median lethal dose (LD50) for Giardia lamblia. Results showed that oregano essential oil showed the best antibacterial activity (66–100 µg/mL), while cinnamon essential oil had the best fungicidal activity (66–116 µg/mL), and both showed excellent antiprotozoal activity (22–108 µg/mL). Regarding the major components, thymol and carvacrol were also good antimicrobials (23–200 µg/mL), and cinnamaldehyde was an antifungal compound (41–75 µg/mL). The major components were grouped according to their chemical structure as phenylpropanoids, terpenoids, and terpinenes. The statistical analysis of the grouped data demonstrated that protozoans were more susceptible to the essential oils, followed by fungi, Gram-positive bacteria, and Gram-negative bacteria. The analysis for the major components showed that the most resistant microbial group was fungi, which was followed by bacteria, and protozoans were also more susceptible. Principal Component Analysis for the essential oils demonstrated the relationship between the biological activity and the microbial group tested, with the first three components explaining 94.3% of the data variability. The chemical structure of the major components was also related to the biological activity presented against the microbial groups tested, where the three first principal components accounted for 91.9% of the variability. The external structures and the characteristics of the cell membranes in the different microbial groups are determinant for their susceptibility to essential oils and their major components

Natural Occurring Phenolic Derivatives from Mauritia flexuosa (Buriti) Stems and Their Potential Antibacterial Activity against Methicillin‐Resistant Staphylococcus aureus (MRSA)

“…In addition to the finding that compounds 1 , 6 and 7 have antibacterial effect on S. aureus strains and have no activity against E. coli , these compounds show either no effect (on C. albicans ) or only weak effect (compound 1 on T. rubrum ) toward fungal species. The lack of effective antifungal activity can be understood in the same way as discussed for bacteria, i. e., the characteristics of both cell wall and cell membranes in the different microbial groups are determinant for their susceptibility to chemicals [36] . Indeed, the fungal cell wall shows an intermediate permeability between Gram‐positive and Gram‐negative bacteria [37] …”

Essential Oil Blends: The Potential of Combined Use for Respiratory Tract Infections

“…49 mg/mL). The antimicrobial effect of essential oils against fungal pathogens has been well studied against the test micro-organisms investigated here-in [ 34 , 35 ]. The genus of Cryptococcus is an important cause of opportunistic fungal infection in severely immunocompromised patients with the primary sites of infection including the lungs [ 36 ].…”

Bioactivity of Essential Oils for Mitigation of Listeria monocytogenes Isolated from Fresh Retail Chicken Meat

“…Seven EOs, namely, cinnamon bark oil (CBO), thyme (wild) oil (TWO), thyme (red) oil (TRO), thyme (geraniol) oil (TGO), coriander oil (CRO), lavender (true) oil (LTO), and rosemary oil (RO), were purchased from National Research Center (NRC Cairo, Egypt) based on their antilisterial activity in a literature survey and their use in traditional medicine [ 7 , 8 , 9 , 10 , 11 , 12 , 15 ] to evaluate their antilisterial activity against MDR L. monocytogenes . EOs were stored at 4 °C for further experiments.…”

“…Different preservation methods (chemical preservatives, refrigeration, and heating) have been commonly used throughout food production to control foodborne pathogens. On the other hand, incomplete inactivation of pathogenic agents was widely documented, and post-treatment contamination may reintroduce pathogenic agents into food products [ 7 , 8 , 9 ]. Furthermore, consumers’ fear is increasing concerning the use of chemical preservatives in the food industry due to their possible side effects and toxicity [ 10 ].…”

“…Plant essential oils (EOs) and extracts consider a natural antimicrobial source in the foods industry as preservation and flavoring agents [ 7 , 8 , 9 , 10 , 11 , 12 ]. Plant extracts are generally healthy according to the modern extensive toxicological studies and due to a lack of known adverse impact during historical use [ 10 ].…”