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. 2023 Dec 7;14:1306003. doi: 10.3389/fphar.2023.1306003

TABLE 1.

The antibacterial effectiveness of lavender essential oil against methicillin-resistant Staphylococcus aureus: A systematic review (included studies and their key findings).

Author; year; country Intervention Methodology Objective Key findings
Abers et al., 2021; United States of America Substances: Commercial LEO Strains MRSA and MSSA Modified zone of inhibition assay according to CLSI To evaluate the antimicrobial effectiveness of volatile substances emitted from EOs Vapourised components of lavender oil had low antibacterial activity against S aureus and MRSA. (10–20 mm zone of inhibition)
Adaszynska-Skwirzynska et al., 2020; Poland Substances: Commercial LEO (L. angustifolia) and gentamycin. 1. Chromatographic analysis on LEO. To evaluate whether lavender oil exhibited antibacterial effects alone and synergistically with gentamycin 1. LEO had a very strong synergistic effect with gentamycin against MRSA and MSSA.
Strains: S. aureus ATCC 25923 and clinically sourced MRSA 2. Microdilution checkerboard for MIC (CLSI). 2. LEO MICs: MSSA: 0.25% v/v, MRSA: 1.25% v/v
3. FIC calculated from MIC. 3. LEO and gentamycin MIC: MSSA: 0.125 μg/ml, MRSA: 32.0 μg/ml
4. Combination checkerboard for synergistic effects of LEO and gentamycin
Bekka-Hadji et al., 2016; Algeria Substances: LEO made by hydrodistillation (L. stoechas). 1. GC/MS analysis of LEO. To evaluate the antibacterial activity of five Algerian medicinal plants from Lamiaceae family against MRSA 1. T. fontanesii, O. glandulosum, and T. numidicus were all more active than lavender oil.
Strains. S. aureus ATCC 25923, MRSA ATCC 43300, MRSA S19 2. In vitro activity tested in aromatogram/disc diffusion assay. 2. Undiluted LEO: moderate activity against MSSA.
3. MIC by broth microdilution (CLSI). 3. LEO anti-MRSA activity: similar to Roller et al.
4. MBC by plating 100 µL from wells of LEO concentration equal or higher than MIC 4. Diameter of L. stoechas Microbial Inhibition zones (mm) for 100%, 50%, 25%, 12.5% and 6.25% oil. For S. aureus ATCC 25923: 17.7 ± 1.8; 11.7 ± 3.0; 08.6 ± 0.8; 08.0 ± 0.2; 07.4 ± 0.7. For MRSA strains: 16.4 ± 0.7 to 17.7 ± 1.2; 13.7 ± 0.3 to 14.4 ± 0.8; 09.1 ± 1.2 to 10.7 ± 0.6; 08.3 ± 1.3 to 08.7 ± 1.0; 06.3 ± 0.2 to 06.6 ± 0.3.
5. LEO MIC and MBC (μL/ml): S. aureus ATCC 25923: 1.20 and 1.20; MRSA ATCC 43300: 4.70 and 9.40; MRSA S19: 0.30 and 1.20
Bona et al., 2019; Italy Substances: LEO made using L. latifolia oil. Strains: 17 clinical MRSA strains, 27 clinical MSSA strains, S. aureus NCTC 6571 1. GC/MS analysis. To test the inhibition efficacy of 12 different essential oils against clinical isolates of S. aureus including MRSA strains 1. No significant difference in efficacy of EOs between MRSA and MSSA.
2. Disc diffusion assay (EUCAST). 2. LEO needed at higher concentration than other oils (oregano, winter savory, basil, and mint) for similar effects.
3. MICs of EO with higher sensitivity than vancomycin calculated with microplate serial dilution MIC (EUCAST). 3. MIC % (v/v): Lavender oil effective against at least 50% of tested strains. MIC: 1–2 against most strains and 0.25 and 0.5 on one occasion.
4. Fluorescein Diacetate Assay 4. Fluorescein Diacetate Assay: LEO reduced metabolic activity by at least 50% at maximum concentration (4%). Sub-MIC concentrations not effective at reducing metabolic activity
Brozyna et al., 2021; Poland Substances: Commercial L. angustifolia LEO. Strains: S. aureus 6,538 and 33,591, Clinically isolated 6 strains of MSSA and 8 strains of MRSA 1. GC/MS analysis. To test the antimicrobial and antibiofilm activity of essential oils in liquid and vapour phase against S. aureus 1. Vapour Phase: No inhibition of growth in most staphylococcus strains.
2. Biofilm biomass level using crystal violet Assay. 2. Disc Diffusion: 9–12 mm inhibition zone when used in liquid form, 14 mm of partial inhibition in one case.
3. Biofilm metabolic activity level using tetrazolium chloride staining. 3. MIC: MIC (v/v%) ranged from 0.2 to 3.1.
4. Inverted Petri dish assay. 4. Biofilm: No antibiofilm activity observed in emulsified LEO.
5. Disc diffusion assay. 5. Non-emulsified LEO - only slightly eradicated biofilm, but in some cases, it enhanced the biofilm.
6. Serial microdilution for MIC. 6. LEO also had largest emulsion droplet size, which may have impacted its effectiveness as an antimicrobial agent. LEO droplet size: 3,531 ± 204 nm
7. Minimal biofilm eradication assay.
8. Antibiofilm dressing activity.
9. AntiBioVol method.
10. Dynamic light scattering to measure EO emulsion droplet size
Budzynska et al., 2011; Poland Substances: Commercial LEO (L. angustifolia). 1. MIC by microdilution method with modified CLSI. LEO diluted with ethanol (1:1). Examine the antibiofilm activity of select EOs (including LEO) and some of their major constituents 1. TTO, alpha-terpineol and terpinen-4-ol as well as MEO had stronger anti-biofilm activity than LEO.
Strains:S. aureus ATCC 29213 2. TTC reduction assay to detect eradication of biofilm. 2. MBC was less than 4 x MIC. Against S. aureus, LEO had MIC: 0.78 %v/v, MBC: 1.56 %v/v, MBEC (4 h): 1.56 %v/v, and MBEC (24 h): 1.56 %v/v.
3. Time dependent eradication of biofilm conducted on microplate. 3. Eradication of biofilm on surgical mesh: Needed 4-8x MIC to have >90% eradication of live bacteria.
4. LIVE/DEAD BacLight Bacterial Viability kit to assess viability of cells treated with EOs 4. LEO has some antibiofilm potency
Cui et al., 2021; China Substances: Commercial L. spica EO, combined lavender oil with erythromycin, streptomycin, ampicillin, florfenicol, chloramphenicol, tetracycline, gentamicin, kanamycin, bacitracin, amikacin and vancomycin. 1. Agar well diffusion test for oil alone. To rapidly screen for the ability of 29 essential oils, including lavender oil, to enhance antibiotic activity 1. LEO MIC not noted as strong - 0.625 v/v%.
Strains: MRSA 43300 2. Modified well diffusion method for antibiotic and oil. 2. Optimum concentration to reach acceptable zone of inhibition: 6.25 v/v %.
3. MIC of essential oil with broth microdilution method (CLSI). 3. LEO had high-level enhancement with gentamycin on MRSA 43300.
4. Modified well diffusion method for combination of antibiotic and essential oil. 4. Lavender oil not considered effective enough for time kill assay
5. Time kill assay (not done on LEO)
Di Vito et al., 2021; Italy Substances:LEO and hydrolates made with L. angustifolia and L. intermedia. 1. GC/MS analysis and gravimetric analyses. To compare the antimicrobial activity between essential oils and hydrolates from six Italian aromatic plants (including two lavender species). To compare the concentration of active volatiles in essential oils to hydrolates 1. While essential oils had a lower MIC, the volatiles in the hydrolates had higher antimicrobial effectiveness because they were active at lower concentrations. This is because they are hydrophilic and are more bioavailable than the essential oil.
Strains: Clinical MRSA and MSSA strains 2. Microdilution broth to find MIC and minimum lethal concentration of EOs and hydrolates (EUCAST) 2. Lavandula angustifolia MIC and MBC % (v/v): MRSA: MIC: >2, MBC: >2; MSSA: MIC: >2, MBC: >2.
3. Lavandula intermedia MIC and MBC % (v/v): MRSA: MIC: 2, MBC: >2; MSSA: MIC: 2, MBC: >2.
4. Hydrolates from lavender species did not show antimicrobial effectiveness against MRSA or MSSA. 5. Of the oils tested, lavender had least effectiveness because of the least active chemicals
Edward-Jones et al., 2004; United Kingdom Substances: Commercial LEO (L. angustifolia). 1. Oils loaded on filter paper discs placed on agar plates with S. aureus. To determine the effect of essential oils on MRSA when used in a dressing model 1. Dressing Model: Effectiveness of EO depended on primary layer of dressing. Lavender oil showed some inhibition but wasn’t one of the most effective oils.
Strains: 3 MRSA strains 2. Vapours assessed by putting the discs on the underside of the lid 8 mm away from agar surface. 2. LEO zone of inhibition: 15–21 mm.
3. The most inhibitory combinations of oils were placed onto four layered dressing model 3. MRSA not susceptible to vapours from any essential oil. Lavender oil vapour had no antimicrobial effectiveness
Haba et al., 2014; Spain Substances: Commercial L. angustifolia LEO. Rhamnolipids as an emulsifying agent. 1. Rhamnolipid production and characterisation with LC/MS. To investigate whether essential oil composition influences emulsification with rhamnolipids and their use as antimicrobial agents against MRSA and Candida albicans 1. LEO MIC % (v/v) against MRSA: .
Strains: MRSA ATCC 43300 2. Titration to determine the emulsifying properties of rhamnolipid. 2. Zone of Inhibition (LEO alone): No inhibition effect.
3. Broth microdilution assay and resazurin assay to determine MIC of LEO and rhamnolipids. 3. Zone of Inhibition (LEO emulsion): The least effective emulsion was LEO (10.0 mm).
4. Agar-well diffusion to assess antimicrobial activity of emulsions. Emulsions had a high EO content, within therapeutic range. LEO emulsions concentration: 78.7/8.5/12.8 (% water/rhamnolipid/EO) 4. The concentrations of LEO used are safe for topical use, but other EOs showed more effective inhibition
Kırmızıbekmez et al., 2009; Turkey Substances: oil made from L. stoechas. 1. GC-FID and GC/MS analysis on oil. To assess the chemical composition and antimicrobial activity of L stoechas that grow wild in Turkey 1. Flower essential oil was more active than the leaf oil towards the tested pathogenic microorganisms.
Strains: Clinical strain of MRSA 2. Broth microdilution for MIC. 2. MRSA was more susceptible to LEO extracted from flowers (MIC = 31.2 μg/ml).
3. TLC-bioautographic DPPH assay to detect free-radical scavenging activity of the samples 3. The most susceptible microorganism was MRSA, which when treated with the leaf and flower oils, produced MICs of 125 and 31.2 μg/ml, respectively
Koca et al., 2019; Turkey Substances: L. intermedia oil. Broth microdilutions to determine MIC (CLSI guidelines) To investigate the antimicrobial effect of essential oils obtained from Mediterranean region plants on microorganisms isolated as secondary skin infections in patients with Grade II and III acute radiation dermatitis 1. L. intermedia MIC (µg/ml) against MRSA: 188, MSSA: 94, MRCNS: 188, and MSCNS: 47.
Strains: Nine pathogenic strains isolated from 20 clinical samples. Pathogens isolated: MRSA, MSSA, MRCNS, MSCNS 2. L. intermedia was an effective antimicrobial against S. aureus isolated from acute radiation dermatitis
Kot et al., 2019; Poland Substances: EO made from L. angustifolia. 1. GC-FID analysis on oil. To examine the chemical compositions and antibacterial activity of EOs of five Lamiaceae species native to Poland to determine their potential for use against clinical MDR MRSA strains. 1. LEO activity against MDR MRSA was low efficiency.
Strains: 18 strains of clinically isolated MDR MRSA 2. Two-fold serial dilution to determine MIC. 2. LEO MIC values for most strains were 3.12 mg/ml and for some strains 6.26–12.5 mg/ml.
3. MIC values carried out by resazurin microtiter plate assay. No colour change indicated the MIC reached. 3. LEO MBC values for most strains were 4 MIC and 8 MIC (Ranging from 3.12 mg/ml to 100 mg/ml).
4. MBC calculated by pipetting samples from wells that had MIC and incubating onto agar plates 4. Reason - this may be because this oil had fewer active compounds of linalool and linalyl acetate
Kwiatkowski et al., 2019; Poland Substances: Commercial L. angustifolia. 1. Broth microdilution to determine MIC. Done according to CLSI standards with slight modifications. To investigate the impact of LEO on OCT efficiency towards MRSA. 1. Both OCT and LEO showed antibacterial activity individually against MRSA clinical strains. LEO MIC: 13.72 ± 0 to 18.29 ± 7.92 mg/ml; OCT MIC: 1.95 ± 0.00 μg/ml to 3.91 ± 0.00 μg/ml; LEO MBC: 27.44–439 μg/ml.
Strains: 4 strains of MRSA 2. MBC of LEO calculated by inoculating MIC wells. 2. LEO synergistically increased OCT’s susceptibility against MRSA strains and enhanced its effect as an antiseptic. LEO-OCT MIC: 1.29 ± 0.49 mg/ml (0.13 ± 0.05%).
3. Checkerboard assay for synergistic effect of LEO and OCT. 3. FIC and FICI noted, LEO and OCT had synergistic effect against all MRSA strains.
4. Time-Killing Curves. 4. Time-kill assay for MRSA strains showed synergy between LEO and OCT. LEO likely allowed more OCT to permeate into cell.
5. FTIR Analysis. 5. FTIR analysis: There were cell wall modifications in MRSA strains cultured in media supplemented with OCT or LEO/OCT.
6. Calculated FIC and FICI of OCT-LEO 6. EOs likely act on cytoplasmic membrane causing a loss of membrane stability and increased permeability
Man et al., 2019; Romania Substances: Commercial L. angustifolia EO. Two adapted broth microdilution methods (CLSI 2018) to account for hydrophobicity of oil. To investigate the effect of some commonly used essential oils in micellar and aqueous extract on some of the most common pathogenic bacteria 1. Lavender oil had a very low MIC, but a very high MBC. This is because some components affected cell division. MIC % (v/v): Lavender MiEO: 3.1% MRSA, 3.1% MSSA; Lavender AqEO: 25% MSSA, 50% MRSA. MBC: not reached for LEO micelles or aqueous solutions.
Strains: MSSA and MRSA 1. Made homogenous micelles of water and EO that could mix with water-based liquid culture medium. 2. Better results achieved with micelles than aqueous solution, and aqueous solutions were less effective than ethanol on all bacteria.
2. The second method followed the antimicrobial activity of hydrosoluble components of EOs. 3. Micelles likely exhibited antibacterial activity due to high levels of linalyl-butyrate (26.5%), and the soluble linalool (25%) was the likely inhibitory agent in the aqueous extract.
3. HPLC analysis to assess chemical content of EO. 4. Negligible differences noticed between LEO’s effects against MSSA and MRSA.
4. Spot inoculation on checkerboard pattern of last 3 microplate wells from MIC to find MBC 5. MRSA was less susceptible to AqEO than MSSA.
6. Gram-positive peptidoglycan cell wall allows hydrophobic molecules to penetrate and reach the internal environment.
7. Hydrophobicity of EOs likely disrupted bacterial structures, degrading the cell wall and cytoplasmic membrane This caused cytoplasm coagulation and diffusion through the double lipid layer of the membrane, altering permeability and function
Mesic et al., 2021; Bosnia and Herzegovina Substance: Commercial L. angustifolia EO. 1. Allium cepa assay to evaluate genotoxic potential of chemicals. To investigate the cyto/genotoxic effects of lavender and immortelle EOs using plant cells (Allium cepa) and human lymphocytes, as well as their antimicrobial potential using nine strains of bacteria and fungi 1. LEO had cytotoxic and genotoxic effects on A. cepa root cells and in the lymphocyte assay.
Strains: S. aureus ATCC 25923, MRSA ATCC 33591 2. Peripheral blood lymphocyte culture to test for potential mutagenic effects. 2. LEO exhibited very strong antimicrobial activity, and inhibited growth of all tested microbial strains in various degrees. (p ≤ 0.05).
3. Disc diffusion assay according to National Committee for Clinical Laboratory Standards 3. LEO significantly inhibited growth of MDR MRSA in all tested concentrations.
4. Higher antibacterial activity of LEO noted against Gram-positive bacteria, especially against S. aureus.
5. Zone of inhibition (mm). For S. aureus: Pure EO: 46.17 ± 1.04 mm; 750 μg/ml EO: 46.50 ± 0.50 mm; 500 μg/ml EO: 31.50 ± 0.50 mm; 250 μg/ml EO: 33.50 ± 1.50 mm. For MRSA: Pure EO: 27.67 ± 2.52 mm; 750 μg/ml EO: 31.50 ± 0.50 mm; 500 μg/ml EO: 31.67 ± 4.16 mm; 250 μg/ml EO: 21.67 ± 1.53 mm.
6. Antimicrobial activity acts on phospholipid layer of bacterial cell structure
Oancea et al., 2019; Romania Substances: LEO made with L. officinalis and L. angustifolia (wild). 1. Hydrodistillation to make oil. To investigate the physical and chemical makeup of 4 plant-source cosmetic waters and 7 EOs and evaluate their antibacterial properties 1. Wild lavender had more inhibition than regular lavender.
Strains: MRSA 2. Disk diffusion assay 2. Zone of inhibition: L. officinalis EO–17 mm; Wild L. angustifolia EO–20 mm
Predoi et al., 2018; Romania Substances: LEO made from L. angustifolia. 1. Dynamic light scattering measurements. To investigate the direct, synergistic, and indirect antibacterial activities of lavender essential oil, basil essential oils and hydroxyapatite against different human pathogenic Gram-positive and Gram-negative strains 1. LEO had good inhibitory growth activity.
Strains: MRSA 1144, S. aureus 1,426 2. GC/MS analysis on EO. 2. HapL material significantly enhanced antimicrobial activity when coated with low concentrations of LEO for all strains.
3. Adapted diffusion method on agar plates to measure antimicrobial activity. 3. Inhibition zones: LEO: S. aureus: 25 ± 1mm, MRSA: 24 ± 0.5mm; HapL: S. aureus: 13 ± 2mm, MRSA: 10 ± 2 mm.
4. Microdilution broth method to determine MIC and MBC. 4. MIC: LEO: S. aureus: 0.78% (v/v), MRSA: 0.78% (v/v); HapL: S. aureus: 0.31 mg/ml, MRSA: 0.31 mg/ml.
5. Flow cytometry assay to detect antimicrobial action 5. MBC: LEO: S. aureus: 1.56%, MRSA: 1.56%. HapL: S. aureus: 0.62 mg/ml, MRSA: 0.62 mg/ml.
6. Stated - Gram-positive bacteria has a thick layer of peptidoglycan that can inhibit the membrane-disrupting action of EO.
7. Flow cytometry - LEO did not show strong depolarisation of bacterial membrane in MRSA or S. aureus
Ribeiro et al., 2020; Belgium Substances: Commercial L. stoechas
Strains: MSSA, 2 strains of MRSA		 1. GC/MS Analysis.
2. Evaluated cytotoxic EO activity against human keratinocyte and fetal epithelial cell lines.
3. Direct activity tested with broth microdilution to find MIC (CLSI).
4. Synergistic activity between EOs and antibiotics tested with broth microdilution. Used to determine FIC and FICI.
5. LEO’s indirect activity tested with broth microdilution. EO at sub-MIC concentrations added with antibiotics. EO considered to have indirect effect if MIC. Sub-MIC concentration has been fixed at a non-cytotoxic concentration		 To enhance or restore the activity of the antibiotic (on a resistant strain) without introducing a new active compound in the resistance equation 1. Direct ability: Spanish lavender had no antimibacterial effect against S. aureus strains. MIC was all >1,000 μg/ml.
2. Indirect ability: Almost all combinations showed an additive or a synergistic effect against MRSA.
3. Against MRSA, Spanish lavender decreased the MIC of penicillin V by 64-fold from 4 μg/ml to 0.06 μg/mL. As MIC of penicillin V against the MSSA was 0.015 μg/ml, LEO could potentially restore activity of penicillin V on MRSA to that of MSSA.
4. Amoxicillin MIC was decreased by eight times when combined with Spanish lavender.
5. Suggested that EOs are lipophobic and can penetrate and accumulate in the phospholipidic membrane.
6. Synergistic activity: Spanish lavender only had additive effect when tested for synergistic activity
Roller et al., 2009; United Kingdom Substances: Four commercial lavender oils (L. angustifolia. L. latifolia. L. stoechas, and necrodane-rich L. luisieri). 1. Testing vapour: Disc with oil was placed on underside of Petri dish lid in the centre. To compare the antimicrobial efficacy of several lavender oils, used singly and in combination, on MSSA and MRSA 1. All 4 LEOs inhibited growth of MSSA and MRSA by direct contact, but not in the vapor phase. Inhibition zones 28–33 mm at oil 20 μL, increasing with dose.
Strains: MSSA and clinical isolate of MRSA 2. Disc diffusion method. 2. Oils had similar zones irrespective of chemical composition of the oils or S. aureus strain.
3. Vapour diffusion method 3. Most LEO combinations showed inhibition zones similar to those when oils used individually, but necrodane rich L. luisieri oil with L. stoechas or L. langustifolia produced inhibition zones that were two times bigger than when each oil used individually.
4. Difference in MRSA & MSSA sensitivities were insignificant.
5. Acknowledged that disc diffusion may be inaccurate for hydrophobic substances
Said et al., 2015; Portugal Substances: EO made from L. coronopifolia. 1. GC/MS Analysis. To analyse composition of EO of L. coronopifolia from Morocco and evaluate its in vitro antibacterial activity against antibiotic-resistant bacteria isolated from clinical infections 1. Clear bactericidal effect of L. coronopifolia EO against MRSA.
Strains: Clinical MRSA 2. Broth microdilution for MIC and MBC. 2. MIC: 1% (v/v), MBC: 2%.
3. Disc diffusion 3. LEO was effective against almost all bacteria studied, with the highest activity against MRSA, producing a 16 mm zone of inhibition
Voravuthikunchai et al., 2012; Thailand Substances: EO made from L. angustifolia EO. 1. Hydrodistillation to extract EO. To check the effectiveness of selected EOs against different pathogenic bacteria in solid phase by disk diffusion; to evaluate their effectiveness in vapour phase; and to apply the atmosphere generated by the most effective EOs in a portable air conditioning prototype 1. LEO showed moderate inhibitory effect in agar disc diffusion.
Strains: 11 clinical isolates of MRSA 2. Paper disc agar diffusion (CLSI). 2. For LEO - Zone of inhibition: S. aureus ATCC 25923: 18 ± 1mm, MRSA: 12 ± 1mm; MIC: S. aureus ATCC 25923: 1:16, MRSA 1:8; MBC: S. aureus ATCC 25923 1:8, MRSA 1:8; Vapour contact inhibition zones: S. aureus: 18 ± 1mm, MRSA: 12 ± 1 mm.
3. Vapour diffusion assay. 3. For oil blend containing 23% LEO - Inhibition zones: S. aureus ATCC 25923: 28 ± 1mm, MRSA: 25 ± 1mm; MIC: S. aureus ATCC 25923: 1:16, MRSA: 1:16; MBC: S. aureus ATCC 2593: 1:16, MRSA: 1:32; also reduced the CFU of S. aureus and MRSA in the air-conditioning model within 1st hour: S. aureus 125 to 75 CFU, MRSA 125 to 100 CFU
4. Modified agar microdilution method to determine MIC of EOs that produced inhibition zones.
5. Agar dilution method on EOs with significant efficacy to determine MBC.
6. Airconditioning model: EO was placed into closed aircon system. Inoculated Petri dish placed in aircon environment for 8-h intervals up to 24 h. Mean colony counts recorded
Warnke et al., 2009 Substances: Commercial LEO. Agar diffusion test To evaluate the antibacterial and antimycotic efficacy of different EOs on frequently isolated and hospital-acquired bacterial strains including MRSA 1. LEO had antibactbial effect on all S. aureus strains.
Strains: S. aureus ATCC 25923, S. aureus VA 10465/02, MRSA 2. LEO Zone of inhibition: S. aureus ATCC25923: 10mm, S. aureus VA 10465/02: 11mm, MRSA VA 10492/02: 12 mm
3. Controls: ethanol (70%): 9mm, Povidone: 14mm, H2O2: 15mm, Chlorhexidine: 16mm, Olive oil: 0mm, Paraffin oil: 0 mm.
4. EOs often diluted with ethanol, so used ethanol as control, suggested - if EO’s zone of inhibition higher than ethanol, the antibacterial effect was due to EOs.
5. Effect not just because of oil nature, as olive oil and paraffin oil had no inhibitory effect. 6. Size of zone depended on solubility, so size was not direct indicator of antimicrobial effectiveness, instead indicated presence of antimicrobial effect

Abbreviations: LEO, Lavender essential oil; MRSA, methicillin-resistant Staphylococcus aureus; MSSA, methicillin-sensitive Staphylococcus aureus; CLSI, Clinical and laboratory standards institute; MIC, minimal inhibition concentration; FIC, fractional inhibition concentration; ATCC, American Type Culture Collection, GC/MS, analysis–gas chromatography/mass spectrometry analysis, LC/MS, liquid chromatography/mass spectrometry, MBC, minimal bactericidal concentration; EUCAST, European Committee on Antimicrobial Susceptibility Testing, AntiBioVol - antibiofilm activity of volatile compounds, EO, Essential Oil; TTC, 2,3,5-triphenyltetrazolium chloride, TTO, Tea tree oil; MEO, Melissa essential oil; MLC, minimal lethal concentration; GC-FID, gas chromatography flame ionisation detection, TLC-bioautographic DPPH, assay - Thin Layer Chromatography bioautographic 2,2-diphenyl-1-picrylhydrazyl assay, MRCNS, methicillin-resistant coagulase negative Staphylococcus; MSCNS, methicillin sensitive coagulase negative Staphyloccocus, MDR MRSA, multidrug resistant MRSA, OCT, octenidine; HPLC, analysis - High-performance liquid chromatography analysis, MiEO, micelle solution of essential oil, AqEO, aqueous phase of essential oil, HapL –hydroxyapatite coated with lavender essential oil, FTIR, analysis - Fourier Transform Infrared Spectroscopy analysis; FICI, Fractional inhibitory concentration indices; CFU, colony forming units; OCT-LEO, octenidine and lavender essential oil.