Anti microbial activity of Essential Oils

Anti microbial activity of Essential Oils

Brief HistoryEssential oils have been present in many products for thousands of years. Perfumes, food (both unprocessed and processed), beverages are a common example.

For many years, it has been observed that Essential oils have antimicrobial properties such as - inhibition of microbial growth-destruction of Biofilms and microbial spores- preservative for both processed and unprocessed food-pharmaceuticals (eg. Lagundi extract)-alternative medicines and natural therapies

Applicationsin vitrodirect application to skin inhalationingestion.

In nature Essential oils play an important role as protection of plants. They are the secondary metabolites capable of inhibiting/slowing growth of microbes(yeast,bacteria mold). They have activities against the membrane and cytoplasm and membranes, and in some cases even completely change morphology of cells.However, it is not yet fully understood how essential oils work as a whole

Chemical composition

Rosemary (Rosmarinus officinalis L.)

Carnosol Carnosic Acid Rosmanol

Components of an Essential OilTerpenes inhibit toxin accumulation and discharge them from liver and kidneysEsters anti-fungal, calming, anti-inflammatory, anti-bacterial, anti-viralOxides expectorant, antiseptic, anaestheticAlcohols antiseptic, anti-viral, anti-bacterial, stimulate immunes systemPhenols fragrance, antiseptic, anti-bacterial, possibly anti-cancerousKetones stimulate cell regeneration, loosen mucousAldehydes anti-infectious, sedative, topical irritants, calming when inhaled

ActivitiesYeast and MoldsBacteriaGram (+) BacteriaGram(-) BacteriaGram Positive Bacteriamore susceptible to EO- Peptidoglycan cell wall structure (90-95%) allows hydrophobic molecules to easily penetrate cells on both cell wall and cytoplasm.

Gram Positive Bacteria

Gram Negative BacteriaComposed of double layer of phospholipids linked to inner membrane by lypopolysacharidesVery thin layer of peptidoglycanVery resistant to EO

In general, The antimicrobial activity of EOs is dependent on the chemical composition and amount of single compounds.The location and orientation of functional groups on the EO affects the microbial activityEffects of Functional groups Integrity and destruction of cell membrane -lypopolysaccahrides (fatty acids)Action on ProteinsATP and ATPasesMetabolomeCell MorphologyAnti-Quorum Sensing activity Chemical reactionsAlcohol - may dehydrate the cell thus affecting the integrity of the cell membrane of bacteria causing it to burst.

Esters with amides- lipopeptides promotes Membrane depolarization of cells

Terpenes-Showed very low or no antimicrobial activity against 25 genera of bacteria when used as a singular compound.

Terpenoids-Terpenes with added oxygen molecules-Microbial activity is related to their functional groups, the hydroxyl groups of phenolic terpenoids and presence of delocalised electrons-Affects membrane permeability -may also decrease the enthalpy any melting temperatue of membrane-may change the fatty acid composition of cell membranes

Phenols-At low concn: can interfere with enzymes, at high concn, can denature proteins.-Phenylpropenes-antimicrobial activity conferred by free hydroxyl groups-also effective on yeasts and moulds-acts against bacterial enzymes, mainly ATP and transport of ions

Other molecules-naturally present in the EOS, may or may not be in active form subjected to particular a/biotic stress affect microbial activity.-amount affects antimicrobial activity

Possible mechanisms of action-affects both external envelope and cytoplasm-hydrophobicity disrupts bacterial structures, leads to increased permeability-destruction of cell membrane, metabolic regulation, turgor pressure disruption, cytoplasm coagulationdamaging membrane proteins, leakage of cell proteinsreducing proton motive force, reduing intracellular ATP, etc.-The overall reaction on the disruption of cell membrane and the lysis of cell due to cytoplasm coagulation cannot be regarded as separate events, rather these may be a consequence of other activities and their concentration.Integrity and destruction of cell membrane

Action on ProteinsDenaturation of proteins affect Cell Division-Inhibition of splitting of cellsInhibition of GTP HydrolysisAnalysis showed that many proteins can either be upregulated or downregulated by presence of thymol, with significant changes in proteins belonging to different fxnl. classThymol can also affect the expression of proteins involved in energy metabolism, DNA and ribosomal proteImpairment of citrate and acetate pathwaysEffect on ATP and ATPases-disruption of the cell membrane alter the intra and extracellular ATP balance such that ATP is lost through the disturbed membrane.Inorganic phosphates may be lost or the proton motive force and changes of some essential ions (K+, H+) may be disruptedEffect on the MetabolomeGlucose tend to accumulate when microbial cells are treated with cavacrol- the inability to metabolise glucose leads to lose in viability.Organic acids (except formate) showed a significant decrease in concn. Inversely proportional to dose of cavacrol.Increase in formate may indicate a possible metabolic shift to fermentationEffects on Cell Morphology-Effects of EOs and components differ depending on the shape of bacteria-rod shaped the most sensitiveEffects on EOs includeMembrane expansionIncreased membrane fluidityInhibition of membrane embedded enzymeCoagulation of cytoplasmic contentsAlteration of composition of fatty acidsCell lysis (leakage of cytoplasmic contents) Anti-Quorum Sensing ActivityQS behaviours occur only when a bacteria reach a specific cell density-these behaviours may be undertaken by a singular bacterium bu become more effective when action is simultaneously performed by a group of bacteriaEOs are Potential as Novel therapies as non-toxic inhibitors of QSN-Acyl Homoserine Lactones (AHL)- signalling molecules for QS.Different mechanisms for QS inhibitionA. Inhibition of AHL SynthesisB. Inhibition of AHL trasport/secretionC. Sequestration of AHLD. Antagonistic ActionE. Inhibition of Targets downstream of AHL receptor bindingOther considerations- The EOS and their components on bacteria still remain a focal are for future research-these can be utilized to make the best use out of their antimicrobial activity to reduce their concentrations to achieve particular effect for food safety and health purposes.Reference:Nazzaro, Filomena et al. Effect of Essential Oils on Pathogenic Bacteria.Pharmaceuticals6.12 (2013): 14511474.PMC. Web. 25 Apr. 2015.