Effect of Essential Oils on Pathogenic Bacteria

In the paper

“The treatment of E. coli 0157:H7 strain EDL 933 and Salmonella enterica subsp enterica serovar typhi strain ATCC 19430 with mustard EO resulted in the loss of intracellular ATP in S. aureus [94].”

What the sources say

• Not checked yetcites [94] Caillet, 2009, Effect of gamma radiation and oregano essential oil on murein and ATP concentration of Staphylococcus aureus, J. Food Sci. source

In the paper

“The treatment of some pathogens, such as E. coli and L. monocytogenes, with eugenol, cinnamaldehyde and carvacrol inhibited the generation of adenosine triphosphate from dextrose and disrupted the cell membrane.”

What the sources say

• Not checked yetcites [45] Gill, 2004, Mechanisms of bactericidal action of cinnamaldehyde against Listeria monocytogenes and of eugenol against L. monocytogenes and Lactobacillus sakei, Appl. Environ. Microbiol. source

In the paper

“It also can perturb the Z-ring morphology in vivo and reduce the frequency of the Z-ring per unit of cell length of E. coli.”

What the sources say

• Not checked yetcites [79] Domadia, 2007, Inhibition of bacterial cell division protein FtsZ by cinnamaldehyde, Biochem. Pharmacol. source

In the paper

“Due to their hydrophobic nature, EOs and/or their components can affect the percentage of unsaturated fatty acids (UFAs) and alter their structure [4].”

What the sources say

• Not checked yetcites [4] Burt, 2003, Antibacterial activity of selected plant essential oils against Escherichia coli O157:H7, Lett. Appl. Microbiol. source

In the paper

“Other proteins, such as the DNA-binding protein H-NS and the 50S ribosomal proteins L7/L12, are down-regulated by thymol.”

What the sources say

• Not checked yetcites [82] Mauriello, 2013, Expression of DnaK, HtpG, GroEL and Tf chaperones and the corresponding encoding genes during growth of Salmonella Thompson in presence of thymol alone or in combination with salt and cold stress, Food Res. Int. source

In the paper

“However, although similar concentrations of eugenol or carvacrol (5 to 10 mM) may have a bactericidal effect on E. coli and L. monocytogenes, there are large differences in response between the three organisms to cinnamaldehyde, which has bactericidal activity against E. coli and L. monocytogenes, at 10 mM and 30 mM concentrations [45].”

What the sources say

• Not checked yetcites [45] Gill, 2004, Mechanisms of bactericidal action of cinnamaldehyde against Listeria monocytogenes and of eugenol against L. monocytogenes and Lactobacillus sakei, Appl. Environ. Microbiol. source

In the paper

“Thymol up-regulates the OM channel protein TolC that is involved in the formation of an efflux system that represents [83] an important mechanism of resistance to detergents and bile salts in Salmonella and may also be involved in resistance to thymol.”

What the sources say

• Not checked yetcites [83] Baucheron, 2005, TolC but not AcrB is essential for multidrugresistant Salmonella enterica serotype Typhimurium colonization of chicks, J. Antimicrob. Chem. source

In the paper

“Thymol can also affect the expression of proteins involved in energy metabolism, such as enolase, which is more than 10-fold up-regulated in thymol-treated cells, the 2,3-bisphosphoglycerate-dependent phosphoglycerate mutase dPGM and the glyceraldehyde-3-phosphate dehydrogenase A, which are down-regulated [82].”

What the sources say

• Not checked yetcites [82] Mauriello, 2013, Expression of DnaK, HtpG, GroEL and Tf chaperones and the corresponding encoding genes during growth of Salmonella Thompson in presence of thymol alone or in combination with salt and cold stress, Food Res. Int. source

In the paper

“Treatment with thymol causes the up-regulation of some proteins and can trigger bacterial envelope stress due to the accumulation of mis-folded OM proteins.”

What the sources say

• Not checked yetcites [82] Mauriello, 2013, Expression of DnaK, HtpG, GroEL and Tf chaperones and the corresponding encoding genes during growth of Salmonella Thompson in presence of thymol alone or in combination with salt and cold stress, Food Res. Int. source

In the paper

“Cinnamaldehyde can also inhibit the rate of GTP hydrolysis and binds to FtsZ with favourable enthalpic interactions.”

What the sources say

• Not checked yetcites [79] Domadia, 2007, Inhibition of bacterial cell division protein FtsZ by cinnamaldehyde, Biochem. Pharmacol. source

In the paper

“YidC depletion leads to a decrease in the functional assembly of cytochrome o oxidase and F1Fo ATPase and a strong reduction in the proton motive force in E. coli [90].”

What the sources say

• Not checked yetcites [90] Urbanus, 2003, A conserved function of YidC in the biogenesis of respiratory chain complexes, Proc. Nat. Acad. Sci. USA source

In the paper

“Treatment with thymol, carvacrol and eugenol, which are all phenolic compounds, may increase the amount of saturated C16 (and shorter length) fatty acids, increase the amount of saturated C18 and decrease the amount of unsaturated C18 fatty acids in the bacterial membrane.”

In the paper

“In some cases, cells defective in the production of UFAs can continue to grow and synthesise phospholipids, but they eventually begin to lose metabolites and subsequently lyse.”

In the paper

“The concentration of aromatic amino acids remained stable at the lowest level of carvacrol but increased at higher doses.”

What the sources say

• Not checked yetcites [107] Picone, 2013, Evaluation of the effect of carvacrol on the Escherichia coli 555 metabolome by using 1H-NMR spectroscopy, Food Chem. source

In the paper

“Indeed, the S. typhimurium cell membrane was altered by carvacrol and thymol, and some of the cells showed swelling after treatment with thymol.”

In the paper

“The septa were present between the filamentous cells, but its formation was incomplete.”

What the sources say

• Not checked yetcites [98] Kwon, 2003, Bactericidal effects and inhibition of cell separation of cinnamic aldehyde on Bacillus cereus, Lett. Appl. Microbiol. source

In the paper

“Formate increased until a certain dose of carvacrol and then drastically decreased to nearly zero; the increase in formate (one of the main sugar molecules produced by E. coli during fermentation) may indicate a possible metabolic shift toward fermentation.”

What the sources say

• Not checked yetcites [107] Picone, 2013, Evaluation of the effect of carvacrol on the Escherichia coli 555 metabolome by using 1H-NMR spectroscopy, Food Chem. source

In the paper

“Cells treated with cinnamaldehyde for 1 h showed a strong inhibition of cell separation and appeared as filamentous cells.”

What the sources say

• Not checked yetcites [98] Kwon, 2003, Bactericidal effects and inhibition of cell separation of cinnamic aldehyde on Bacillus cereus, Lett. Appl. Microbiol. source

In the paper

“They found that glucose tends to accumulate when microbial cells are treated with carvacrol, and the inability of the cells to metabolise the glucose leads to a loss of viability.”

What the sources say

• Not checked yetcites [107] Picone, 2013, Evaluation of the effect of carvacrol on the Escherichia coli 555 metabolome by using 1H-NMR spectroscopy, Food Chem. source

In the paper

“S. typhimurium and Pseudomonas spp. cells treated with cinnamaldehyde and limonene presented external modifications, suggesting that these compounds penetrated the cell envelope and altered its structure.”

In the paper

“B. thermosphacta exhibited evident alterations after treatment with cinnamaldehyde, limonene and eugenol; eugenol often induced swelling and occasionally disrupted the external envelope.”

In the paper

“After 24 h of treatment with the EO of mint, cellular damage of rod bacteria was observed by Hafedh et al. [110], whereas the damage was less evident in coccoid bacteria.”

What the sources say

• Not checked yetcites [110] Hafedh, 2009, Biological activities of the essential oils and methanol extract of two cultivated mint species (Mentha longifolia and Mentha pulegium) used in the Tunisian folkloric medicine, World J. Biotec. Microbiol. source

In the paper

“The activity of EOs and/or their components differs depending on the shape of the bacteria studied, and rod shaped bacterial cells have been reported to be more sensitive to EOs than coccoid cells.”

What the sources say

• Not checked yetcites [110] Hafedh, 2009, Biological activities of the essential oils and methanol extract of two cultivated mint species (Mentha longifolia and Mentha pulegium) used in the Tunisian folkloric medicine, World J. Biotec. Microbiol. source

In the paper

“Volatile organic compounds, such as those produced by the rhizospheric bacteria Pseudomonas fluorescens B-4117 and Serratia plymuthica IC1270, may inhibit the cell-cell communication QS network mediated by AHL signalling molecules produced by various bacteria, such as Agrobacterium, Chromobacterium, Pectobacterium and Pseudomonas.”

In the paper

“The EOs of lavender, roses, geraniums, cloves and rosemary are also able to inhibit QS, whereas orange and juniper EOs appear to have no anti-QS properties [126,127,128,129,130,131].”

What the sources say

• Not checked yetcites [126] Méndez-Vilas, A. (2011). Science Against Microbial Pathogens: Communicating Current Research and Technological Advances, Brown Walker Press.
• Not checked yetcites [127] Cox, 2005, Effects of a topical essential oil-containing formulation on bio-film-forming coagulase-negative staphylococci, Lett. Appl. Microbiol. source
• Not checked yetcites [128] Khan, 2009, Inhibition of quorum sensing regulated bacterial functions by plant essential oils with special reference to clove oil, Lett. Appl. Microbiol. source
• Not checked yetcites [129] Zaki, 2013, Assessment of anti-quorum sensing activity for some ornamental and medicinal plants native to Egypt, Sci. Pharm. source
• Not checked yetcites [130] Varga, 2010, Inhibition of quorum-sensing signals by essential oils, Phytother. Res. source
• Not checked yetcites [131] Chernin, 1998, Chitinolytic activity in Chromobacterium violaceum: Substrate analysis and regulation by quorum sensing, J. Bacteriol. source

In the paper

“The exchange between the hydroxyl group and a methyl ether in carvacrol can affect its hydrophobicity and antimicrobial activity.”

In the paper

“For instance, trans-cinnamaldehyde can inhibit the growth of E. coli and S. typhimirium without disintegrating the OM or depleting intracellular ATP.”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source
• Not checked yetcites [14] Helander, 1997, Polyethyleneimine is an effective permeabilizer of Gram negative bacteria, Microbiology source

In the paper

“For instance, thymol and carvacrol have similar antimicrobial effects but have different mechanisms of action against Gram-positive and Gram-negative bacteria.”

In the paper

“The antimicrobial activity of most terpenoids is related to their functional groups, and the hydroxyl group of the phenolic terpenoids and the presence of delocalised electrons are important elements for their antimicrobial action.”

In the paper

“Carvone is also ineffective against the OM and does not affect the cellular ATP pool [13,14].”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source
• Not checked yetcites [14] Helander, 1997, Polyethyleneimine is an effective permeabilizer of Gram negative bacteria, Microbiology source

In the paper

“Their effect depends on the amount of the compound present; at low concentrations, they can interfere with enzymes involved in the production of energy, and at higher concentrations, they can denature proteins [7].”

What the sources say

• Not checked yetcites [7] Tiwari, 2009, Application of natural antimicrobials for food preservation, J. Agric. Food Chem. source

In the paper

“The antimicrobial activity of other molecules, such as limonene and p-cymene, depends on the alkyl group. Thus, in some cases, limonene can be considered to be more effective than p-cymene [12].”

What the sources say

• Not checked yetcites [12] Dorman, 2000, Antimicrobial agents from plants: Antibacterial activity of plant volatile oils, J. Appl. Microbiol. source

In the paper

“The OM is, however, almost but not totally impermeable to hydrophobic molecules, some of which can slowly traverse through porins [10,11].”

What the sources say

• Not checked yetcites [10] Plesiat, 1992, Outer membranes of Gram-negative bacteria are permeable to steroid probes, Mol. Microbiol. source
• Not checked yetcites [11] Neidhardt, F.C. (1996). Escherichia coli and Salmonella: Cellular and Molecular biology, ASM Press.

In the paper

“Small hydrophilic solutes are able to pass through the OM via abundant porin proteins that serve as hydrophilic transmembrane channels, and this is one reason that Gram-negative bacteria are relatively resistant to hydrophobic antibiotics and toxic drugs [8,9].”

What the sources say

• Not checked yetcites [8] Nikaido, 1994, Prevention of drug access to bacterial targets: Permeability barriers and active efflux, Science source
• Not checked yetcites [9] Vaara, 1992, Agents that increase the permeability of the outer membrane, Microbiol. Rev. source

In the paper

“The EOs and their components have a variety of targets, particularly the membrane and cytoplasm, and in certain situations, they completely alter the morphology of the cells.”

In the paper

“p-Cymene does not affect the membrane permeability but may decrease the enthalpy and melting temperature of membrane [24]; these properties strengthen the notion that this compound may act as a substitutional impurity in the membrane.”

What the sources say

• Not checked yetcites [24] Cristani, 2007, Interaction of four monoterpenes contained in essential oils with model membranes:implications for their antibacterialactivity, J. Agric. Food Chem. source

In the paper

“Fitzgerald et al. [49] observed that vanillin’s primary target is the membrane but reported that other targets may be present within the microbial cell.”

What the sources say

• Not checked yetcites [49] Fitzgerald, 2005, Structure-function analysis of the vanillin molecule and its antifungal properties, J. Agric. Food Chem. source

In the paper

“Isoeugenol is more active against bacteria than eugenol and is also effective against yeasts and moulds [39,42,43].”

What the sources say

• Not checked yetcites [39] Laekeman, 1990, Eugenol a valuable compound for in vitro experimental research and worthwhile for further in vivo investigation, Phytother. Res. source
• Not checked yetcites [42] Zemek, 1979, Antibiotic properties of lignin components, Folia Microbiol. source
• Not checked yetcites [43] Zemek, 1987, Antimicrobial properties of aromatic compounds of plant origin, Folia Microbiol. source

In the paper

“The antimicrobial activity of the phenylpropenes also depends on the type and number of substitutions on the aromatic ring and similar to most other EOs, on the microbial strain and conditions in which the EO is tested [41].”

What the sources say

• Not checked yetcites [41] Pauli, 2010, Antimicrobial properties of volatile phenylpropanes, Nat. Prod. Commun.

In the paper

“The activity of carvacrol seems to be linked to the presence of a hydroxyl group that may function as a trans-membrane carrier of monovalent cations by carrying H+ into the cell cytoplasm and transporting K+ back out [18,19].”

What the sources say

• Not checked yetcites [18] Ultee, 2002, The phenolic hydroxyl group of carvacrol is essential for action against the food-borne pathogen Bacillus cereus, Appl. Environ. Microbiol. source
• Not checked yetcites [19] Combes, 2006, Antimicrobial activity of carvacrol related to its chemical structure, Lett. Appl. Microbiol. source

In the paper

“Burt et al. [25] demonstrated that although the compound did not affect protein synthesis in E. coli, it did affect the membrane potential.”

What the sources say

• Not checked yetcites [25] Burt, 2007, Carvacrol induces heat shock protein and inhibits synthesis of flagellin in Escherichia coli O157:H7, Appl. Environ. Microbiol. source

In the paper

“It causes the release of LPS [13] and also acts on cytoplasmic membrane to alter the transport of ions.”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source

In the paper

“However, even cells with flagella exhibited decreased motility that was depended upon the amount of carvacrol, indicating that the compound also diminished the proton motive force needed to drive flagellar movement [38].”

What the sources say

• Not checked yetcites [38] Gabel, 2003, The speed of the flagellar rotary motor of Escherichia coli varies linearly with proton motive force, Proc. Natl. Acad. Sci. USA source

In the paper

“p-Cymene shows a high affinity for microbial membranes and can perturb the membranes, causing them to expand and affecting the membrane potential of intact cells [18].”

What the sources say

• Not checked yetcites [18] Ultee, 2002, The phenolic hydroxyl group of carvacrol is essential for action against the food-borne pathogen Bacillus cereus, Appl. Environ. Microbiol. source

In the paper

“There is also limited evidence that carvacrol affects periplasmic enzymes and membrane proteins [30], and it may also have intracellular targets [37].”

What the sources say

• Not checked yetcites [30] Juven, 1994, Factors that Interact with the antibacterial action of thyme essential oil and its active constituents, J. Appl. Bacteriol. source
• Not checked yetcites [37] Kocsis, 2009, Effect of thyme (Thymus vulgaris L.) essential oil and its main constituents on the outer membrane protein composition of Erwinia strains studied with microfluid chip technology, Chromatographia source

In the paper

“Cinnamaldehyde is generally less powerful than eugenol [45], but when it is used against E. coli and S. typhimurium, its activity is similar to thymol and carvacrol, the most potent EOs [13].”

What the sources say

• Not checked yetcites [45] Gill, 2004, Mechanisms of bactericidal action of cinnamaldehyde against Listeria monocytogenes and of eugenol against L. monocytogenes and Lactobacillus sakei, Appl. Environ. Microbiol. source
• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source

In the paper

“For example, a sub-lethal concentration of the molecule does not affect the integrity of the membrane in E. coli but can inhibit the growth and bioluminescence of the microorganism Photobacterium leiognathi; this suggests that cinnamaldheyde gains access to the periplasm and perhaps also to the cytoplasm [13].”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source

In the paper

“Carvacrol also inhibited the synthesis of another microbial protein, flagellin, and gave rise to cells without flagella that subsequently exhibited decreased motility.”

What the sources say

• Not checked yetcites [25] Burt, 2007, Carvacrol induces heat shock protein and inhibits synthesis of flagellin in Escherichia coli O157:H7, Appl. Environ. Microbiol. source

In the paper

“However, some studies have shown that it inhibits the respiration pathway in E. coli and L. innocua and that it has activity against some lactic acid bacteria, such as L. plantarum, by disrupting K+ and pH homeostasis [48].”

What the sources say

• Not checked yetcites [48] Fitzgerald, 2004, Mode of antimicrobial of vanillin against Escherichia coli, Lactobacillus plantarum and Listeria innocua, J. Appl. Microbiol. source

In the paper

“In some cases, thymol can induce the release of lipopolysaccharides, but it does not affect chelating cations [13].”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source

In the paper

“Cinnamaldehyde has at least three mechanisms of action against bacteria. At low concentrations, it inhibits enzymes involved in cytokine interactions or other less important cell functions, and at higher concentrations, it acts as an ATPase inhibitor. At a lethal concentration, cinnamaldheyde perturbs the membrane.”

In the paper

“The interaction of thymol with the membrane affects membrane permeability and results in the release of K+ ions and ATP [20,27,28].”

What the sources say

• Not checked yetcites [20] Lambert, 2001, A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol, J. Appl. Microbiol. source
• Not checked yetcites [27] Walsh, 2003, Activity and mechanisms of action of selected biocidal agents on Gram-positive and-negative bacteria, J. Appl. Microbiol. source
• Not checked yetcites [28] Xu, 2008, The antibacterial mechanism of carvacrol and thymol against Escherichia coli, Lett. Appl. Microbiol. source

In the paper

“Eugenol alters the membrane, affects the transport of ions and ATP and changes the fatty acid profile of different bacteria.”

In the paper

“Burt et al. [25] showed that E. coli cells grown in the presence of a sub-lethal concentration of carvacrol produced significantly more GroEL, indicating that carvacrol affected protein folding.”

What the sources say

• Not checked yetcites [25] Burt, 2007, Carvacrol induces heat shock protein and inhibits synthesis of flagellin in Escherichia coli O157:H7, Appl. Environ. Microbiol. source

In the paper

“Similar to carvacrol, thymol antimicrobial activity results in structural and functional alterations in the cytoplasmic membrane [26] that can damage the outer and inner membranes; it can also interact with membrane proteins and intracellular targets.”

What the sources say

• Not checked yetcites [26] Sikkema, 1995, Mechanisms of membrane toxicity of hydrocarbons, Microbiol. Rev. source

In the paper

“Thymol integrates within the polar head-groups of the lipid bilayer, inducing alterations of the cell membrane.”

In the paper

“Treatment with p-cymene resulted in decreased cellular motility because the proton motive force is required for flagellar movement.”

What the sources say

• Not checked yetcites [25] Burt, 2007, Carvacrol induces heat shock protein and inhibits synthesis of flagellin in Escherichia coli O157:H7, Appl. Environ. Microbiol. source

In the paper

“These mechanisms include chemical modifications of the cell membrane, cytoplasm, enzymes and proteins, and they can completely change the conformation of the microbial cell.”

What the sources say

• Not checked yetcites [70] Carson, 2002, Mechanism of action of Melaleuca alternifolia (tea tree) oil on Staphylococcus aureus determined by time-kill, lysis, leakage, and salt tolerance assays and electron microscopy, Antimicrob. Agents Chemother. source

In the paper

“In contrast, another study [13] found that carvone was ineffective against the OM of E. coli and S. typhimurium and did not affect their intracellular ATP pool.”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source

In the paper

“The effects of EOs usually lead to the destabilisation of the phospholipid bilayer, the destruction of the plasma membrane function and composition, the loss of vital intracellular components and the inactivation of enzymatic mechanisms.”

In the paper

“In fact, the mechanisms of action of the EOs include the degradation of the cell wall [13,64], damaging the cytoplasmic membrane, cytoplasm coagulation [18,33,65], damaging the membrane proteins, increased permeability leading to leakage of the cell contents [20,30]”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source
• Not checked yetcites [64] Gill, 2006, Disruption of E. coli, Listeria monocytogenes and Lactobacillus sakei cellular membranes by plant oil aromatics, Int. J. Food Microbiol. source
• Not checked yetcites [18] Ultee, 2002, The phenolic hydroxyl group of carvacrol is essential for action against the food-borne pathogen Bacillus cereus, Appl. Environ. Microbiol. source
• Not checked yetcites [33] Ultee, 2000, Adaptation of the food-borne pathogen Bacillus cereus to carvacrol, Arch. Microbiol. source
• Not checked yetcites [65] Gustafson, 1998, Effects of tea tree oil on Escherichia coli, Lett. Appl. Microbiol. source
• Not checked yetcites [20] Lambert, 2001, A study of the minimum inhibitory concentration and mode of action of oregano essential oil, thymol and carvacrol, J. Appl. Microbiol. source
• Not checked yetcites [30] Juven, 1994, Factors that Interact with the antibacterial action of thyme essential oil and its active constituents, J. Appl. Bacteriol. source

In the paper

“In general, EOs act to inhibit the growth of bacterial cells and also inhibit the production of toxic bacterial metabolites.”

In the paper

“The EOs can alter both the permeability and function of membrane proteins.”

In the paper

“Some EOs, such as those found in basil, sage, hyssop, rosemary, oregano and marjoram, are active against E. coli, S. aureus, B. cereus and Salmonella spp. but are less effective against Pseudomonas spp. due to the formation of exopolysaccharides that increase resistance to EOs [5,57].”

What the sources say

• Not checked yetcites [5] Nazzaro, 2009, Chemical composition and in vitro antimicrobial and mutagenic activities of seven lamiaceae essential oils, Molecules source
• Not checked yetcites [57] Burt, 2004, Essential oils: their antibacterial properties and potential applications in foods—A review, Int. J. Food Microbiol. source

In the paper

“Tea tree oil induced damage to the cell membrane structures that was accompanied by decreased viability for all three microorganisms included in their study, and the membrane damage was confirmed as the most likely cause of cell death.”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source

In the paper

“With increasing amount of carvone, Oosterhaven et al. [50] observed a decrease in the growth rate of E. coli, Streptococcus thermophilus and L. lactis and hypothesised that the compound might act by disturbing the metabolic energy status of cells.”

What the sources say

• Not checked yetcites [50] Oosterhaven, 1995, S-carvone as a natural potato sprout inhibiting, fungistatic and bacteristatic compound, Ind. Crops Prod. source

In the paper

“The alteration of membrane permeability and the defects in the transport of molecules and ions result in a “disbalance” within the microbial cell. This subsequently leads to cytoplasm coagulation, the denaturation of several enzymes and of cellular proteins and the loss of metabolites and ions [4].”

What the sources say

• Not checked yetcites [4] Burt, 2003, Antibacterial activity of selected plant essential oils against Escherichia coli O157:H7, Lett. Appl. Microbiol. source

In the paper

“Many of the antimicrobial compounds are constitutively expressed by the plants, and others can be synthesised as mechanism of self-defence in response to pathogens.”

In the paper

“γ-Terpinene does not affect the growth of S. typhimurium [30], whereas α-terpinene inhibited 11 of the 25 bacterial species screened by Dorman and Deans [12].”

What the sources say

• Not checked yetcites [30] Juven, 1994, Factors that Interact with the antibacterial action of thyme essential oil and its active constituents, J. Appl. Bacteriol. source
• Not checked yetcites [12] Dorman, 2000, Antimicrobial agents from plants: Antibacterial activity of plant volatile oils, J. Appl. Microbiol. source

In the paper

“The Gram-negative cell wall does not allow for the entrance of hydrophobic molecules as readily as Gram-positive bacteria; thus, EOs are less able to affect the cell growth of the Gram-negative bacteria [4].”

What the sources say

• Not checked yetcites [4] Burt, 2003, Antibacterial activity of selected plant essential oils against Escherichia coli O157:H7, Lett. Appl. Microbiol. source

In the paper

“Most EOs have a more powerful effect on Gram-positive bacteria than Gram-negative species, and this effect is most likely due to differences in the cell membrane compositions (Figure 1) [3,56,58].”

What the sources say

• Not checked yetcites [3] Chorianopoulos, 2008, Disinfectant test against monoculture and mixed-culture biofilms composed of technological, spoilage and pathogenic bacteria: Bactericidal effect of essential oil and hydrosol of Satureja thymbra and comparison with standard acid-base sanitizers, J. Appl. Microbiol. source
• Not checked yetcites [56] Gutierrez, 2008, The anti-microbial efficacy of plant essential oil combinations and interactions with food ingredients, Int. J. Food Microbiol. source
• Not checked yetcites [58] Marino, 2001, Antimicrobial activity of the essential oils of Thymus vulgaris L. measured using a bioimpedimetric method, Int. J. Food Microbiol. source

In the paper

“Different components of EOs can act on proteins present in bacteria and may affect cell division.”

In the paper

“This increases bacterial DNA stability and inhibits the transcription as further mechanism of protection.”

In the paper

“YidC represents an evolutionarily conserved protein that is required for the growth of E. coli [88,89].”

What the sources say

• Not checked yetcites [88] Serek, 2004, Escherichia coli YidC is a membrane insertase for Sec-independent proteins, EMBO J. source
• Not checked yetcites [89] Samuelson, 2000, YidC mediates membrane protein insertion in bacteria, Nature source

In the paper

“This results in the dispersion of the desaturase enzymes and allows them to act on the membrane fatty acids.”

In the paper

“The adaptation of the cells to the presence of these compounds at a concentration lower than the MIC could result in an increase in the percentage of UFAs responsible for the fluidity of the membrane [35,71], which may indicate a certain mechanism of action against the outer cell envelope that could cause membrane structural alterations observable by SEM.”

What the sources say

• Not checked yetcites [35] Betts, 2007, Membrane toxicity of antimicrobial compounds from essential oils, J. Agric. Food Chem. source
• Not checked yetcites [71] Heath, 2004, Fatty acid biosynthesis as a target for novel antibacterials, Curr. Opin. Invest. Drugs

In the paper

“Other intracellular events may contribute to the intracellular ATP decrease; for example, inorganic phosphate may have been lost by passing through the compromised permeable membrane [93,94,95,96,97], or the proton motive force and changes in the balance of some essential ions, such as K+ and H+, may have been disrupted [36].”

What the sources say

• Not checked yetcites [93] Turgis, 2009, Antimicrobial activity of mustard essential oil against Escherichia coli O157:H7 and Salmonella typhi, Food Control. source
• Not checked yetcites [94] Caillet, 2009, Effect of gamma radiation and oregano essential oil on murein and ATP concentration of Staphylococcus aureus, J. Food Sci. source
• Not checked yetcites [95] Caillet, 2006, Effect of gamma radiation and oregano essential oil on murein and ATP concentration of Listeria monocytogenes, J. Food Prot. source
• Not checked yetcites [96] Abee, 1994, Kinetic studies of the action of lactacin F, a bacteriocin produced by Lactobacillus johnsonii that forms poration complexes in the cytoplasmic membrane, Appl. Env. Microbiol. source
• Not checked yetcites [97] Shabala, 2002, Responses of Listeria monocytogenes to acid stress and glucose availability revealed by a novel combination of fluorescence microscopy and microelectrode ion-selective techniques, Appl. Env. Microbiol. source
• Not checked yetcites [36] Ultee, 1999, Mechanisms of action of carvacrol on the food-borne pathogen, Appl. Environ. Microbiol. source

In the paper

“Again, the activity of the EOs and/or their components is not attributable to a single event; most of the components of the EOs [13,18,48] act on the OM and increase its permeability.”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source
• Not checked yetcites [18] Ultee, 2002, The phenolic hydroxyl group of carvacrol is essential for action against the food-borne pathogen Bacillus cereus, Appl. Environ. Microbiol. source
• Not checked yetcites [48] Fitzgerald, 2004, Mode of antimicrobial of vanillin against Escherichia coli, Lactobacillus plantarum and Listeria innocua, J. Appl. Microbiol. source

In the paper

“This results in membrane expansion, increased membrane fluidity and the inhibition of a membrane-embedded enzyme.”

What the sources say

• Not checked yetcites [26] Sikkema, 1995, Mechanisms of membrane toxicity of hydrocarbons, Microbiol. Rev. source
• Not checked yetcites [114] Sikkema, 1994, Cellular toxicity of lipophilic compounds: Mechanisms, implications, and adaptations, Biocatalysis source

In the paper

“The morphology of the Gram-negative cells was much more affected by carvacrol than the Gram-positive cells due to the presence of an OM in the Gram-negative bacteria and the fact that biological membranes are among the possible targets of carvacrol.”

What the sources say

• Not checked yetcites [120] Alakomi, 2006, Weakening effect of cell permeabilizer on gram-negative bacteria causing biodeterioration, Appl. Environ. Microbiol. source

In the paper

“This suggests that eugenol may be capable of disrupting the membrane and allowing the leakage of intracellular constituents, while the other compounds may only cause structural alterations of the outer envelope.”

What the sources say

• Not checked yetcites [35] Betts, 2007, Membrane toxicity of antimicrobial compounds from essential oils, J. Agric. Food Chem. source

In the paper

“This mechanism may cause the inhibition of ATPase activity, as well as the inhibition of other enzymes and altered bacterial growth [13,27,47,96,98].”

What the sources say

• Not checked yetcites [13] Helander, 1998, Characterization of the action of selected essential oil components on Gram-negative bacteria, J. Agric. Food Chem. source
• Not checked yetcites [27] Walsh, 2003, Activity and mechanisms of action of selected biocidal agents on Gram-positive and-negative bacteria, J. Appl. Microbiol. source
• Not checked yetcites [47] Wendakoon, 1995, Inhibition of amino acid decarboxylase activity of Enterobacter aerogenes by active components in spices, J. Food Prot. source
• Not checked yetcites [96] Abee, 1994, Kinetic studies of the action of lactacin F, a bacteriocin produced by Lactobacillus johnsonii that forms poration complexes in the cytoplasmic membrane, Appl. Env. Microbiol. source
• Not checked yetcites [98] Kwon, 2003, Bactericidal effects and inhibition of cell separation of cinnamic aldehyde on Bacillus cereus, Lett. Appl. Microbiol. source

In the paper

“When E. coli cells were treated with carvacrol, the glycolytic pathway modified the amounts of formate and succinate, two organic acids that are normally present in the Krebs cycle, which together with citrate, indicates a shift from respiration to fermentation and K+ leakage [108].”

What the sources say

• Not checked yetcites [108] Cox, 1998, Tea tree oil causes K+ leakage and inhibits respiration in Escherichia coli, Lett. Appl. Microbiol. source

In the paper

“A possible explanation for the difference in the behaviour of the three bacterial species in response to cinnamaldehyde is that there may be differences in the ability of this small hydrophobic molecule to interact with the outer surface of the cells and thus gain access to the cell membrane.”

In the paper

“Bacteria coordinate both bacterium-bacterium interactions and associations with higher organisms through intercellular communication systems known as quorum sensing (QS) systems.”

In the paper

“Bacterial QS may be inhibited through different mechanisms, including (1) the inhibition of AHL synthesis, (2) the inhibition of AHL transport and/or secretion, (3) the sequestration of AHLs, (4) the antagonistic action and (5) the inhibition of targets downstream of AHL receptor binding [125].”

What the sources say

• Not checked yetcites [125] Nazzaro, 2013, Quorum sensing and phytochemicals, Int. J. Mol. Sci. source

In the paper

“The expression of the QS genes results in the production of chemical signalling molecules that are known as autoinducers or bacterial pheromones.”

In the paper

“The accumulation of a stimulatory amount of the QS molecules can occur only when a specific number of cells, referred to as a quorum, are present [121].”

What the sources say

• Not checked yetcites [121] Bassler, 2002, Small talk: Cell-to-cell communication in bacteria, Cell source

In the paper

“again demonstrating that the activity of plant extracts can be strain-specific and may depend on the QS molecule involved.”

What the sources say

• Not checked yetcites [132] Niu, 2006, Subinhibitory concentrations of cinnamaldehyde interfere with quorum sensing, Lett. Appl. Microbiol. source

In the paper

“These molecules are produced as the bacterial population grows until a threshold concentration perceived by the bacteria is reached, resulting in the activation or repression of specific genes.”

In the paper

“The modified structure of the Gram-negative cell surface could also be interpreted as an adaptive response to stress; in fact, nearly all of the Gram-negative bacteria examined demonstrated greater increase of roughness after carvacrol treatment compared with Gram-positive bacteria.”

What the sources say

• Not checked yetcites [120] Alakomi, 2006, Weakening effect of cell permeabilizer on gram-negative bacteria causing biodeterioration, Appl. Environ. Microbiol. source

In the paper

“QS-controlled behaviours occur only when bacteria reach a specific cell density.”

In the paper

“These behaviours are unproductive if undertaken by a singular bacterium but become effective when the action is simultaneously performed by a group of bacteria.”

In the paper

“QS can regulate a number of activities, such as virulence factor expression, bioluminescence, sporulation, biofilm formation and mating.”

In the paper

“EOs may represent the richest available reservoir of novel therapeutics [122,123,124].”

What the sources say

• Not checked yetcites [122] Hentzer, 2003, Pharmacological inhibition of quorum sensing for the treatment of chronic bacterial infections, J. Clin. Invest. source
• Not checked yetcites [123] Lewis, 2006, Prospects of plant derived antibacterials, Nat. Biotechnol. source
• Not checked yetcites [124] Kumar, 2006, Search for antibacterial and antifungal agents from selected Indian medicinal plants, J. Ethnopharmacol. source