Table 1.

In vitro antimicrobial activity of free EOs and their active components against different types of microbial contaminations.

Target microorganisms	EOs and active components	MICa	Exposure concentration, time	Antimicrobial activity	References
Gram-positive bacteria
S. aureus	Cymbopogon flexuosus	0.06%	0.03–4%, 24 h	Complete inhibition at MIC	Adukwu et al. (2012)
	Origanum compactum	0.031–1%	MIC and 1.5MIC, 0–120 min	Immediately significant reductions at 1-1.5MIC	Bouhdid et al. (2009)
	Melaleuca alternifolia	0.12–0.50%	0–8%, 15–60 min	Significant reduction with 0.5% EO after 60 min	Kwieciński et al. (2009)
	Origanum vulgare L., Carvacrol	2.5–5 μl/ml	0.31–2.5 μl/ml, 24 h	No decrease in microbial counts	dos Santos Rodrigues et al. (2017)
	Carvacrol, CIN, Thymol	0.2–0.4 mg/ml	0.01–4 mg/ml, 24 h	Significant inhibition at MIC Around 3–5 log reductions with 0.5–1 mg/ml EO	García-Salinas et al. (2018)
	Salvia officinalis, Mentha spicata	1.25%	2.5–5%, 6 min	2.3–3.1 log reductions	Vetas et al. (2017)
S. aureus (Biofilms)	Cymbopogon flexuosus	0.06–0.12%	0.06–4%, 24 h	Prevention of biofilm formation at MIC and total loss of viability at 0.125–4%	Adukwu et al. (2012)
	Melaleuca alternifolia	0.12–0.50%	0–8%, 0–120 min	Complete eradication and inhibition of metabolism with 1% EO after 120 min	Kwieciński et al. (2009)
	Origanum vulgare L., Carvacrol	5–10 μl/ml	0.31–2.5 μl/ml, 360 h	Decrease in counts after 216 h exposure to 1.25–2.5 μl/ml	dos Santos Rodrigues et al. (2017)
	Carvacrol, CIN, Thymol	N/A	0.25–1 mg/ml, 24 h	Significant inhibition at MIC Around 3–5 log reductions with 0.5–1 mg/ml EO	García-Salinas et al. (2018)
	Origanum vulgare L.	10 μl/ml	5–10 μl/ml, 10–15 min	Complete removal of S. aureus LPMA63 but not S. aureus LPMA11 biofilms	Dos Santos Rodrigues et al. (2018)
	Carvacrol	5 μl/ml	2.5–5 μl/ml, 10–15 min	Complete removal of all biofilms
	Salvia officinalis, Mentha spicata	0.63–1.25%	5–15%, 6 min	0.8–3 log reductions	Vetas et al. (2017)
S. epidermidis spp.	Mutellina purpurea, α-pinene	0.31–0.625 mg/ml	0.15–2.5 mg/ml, 24 h	Complete inhibition at 0.312–0.625 mg/ml	Sieniawska et al. (2013)
	Cinnamomum burmannii	0.5–1%	MIC, 24 h	Complete inhibition	Nuryastuti et al. (2009)
S. epidermidis spp. (Biofilms)	Mutellina purpurea, α-pinene	0.62–1.25 mg/ml	2.5–10 mg/ml, 24 h	Concentrations >10 mg/ml were needed to eradicate biofilms	Sieniawska et al. (2013)
	Cinnamomum burmannii	1–2%	0.01–2%, 1–24 h	Complete loss of metabolic activity after 3–24 h exposure with detachment of biofilms	Nuryastuti et al. (2009)
Enterococcus spp.	Cymbopogon flexuosus, Thymus vulgaris	0.47–15 mg/ml	MIC, 24 h	Complete inhibition	Quendera et al. (2019)
Enterococcus spp., (Biofilms)	Cymbopogon flexuosus, Thymus vulgaris	N/A	1.9–30 mg/ml, 30 min-1 h	Higher levels of eradication were reported for Aeromonas spp. at 15 and 30 mg/ml for all treatment times
L. monocytogenes	Corydothymus capitatus	0.02%	0.06–0.02%, N/A	At 0.025%, significant effect on murein composition and reduction of intracellular ATP with an increase in extracellular ATP	Caillet et al. (2005); Caillet and Lacroix (2006)
	Origanum vulgare L., Rosmarinus officinalis L.	0.6–10 μl/ml	MIC, 24 h	Significant reduction after 2–8 h exposure	de Medeiros Barbosa et al. (2016)
L. monocytogenes, (Biofilms)	Thyme, Tea tree	0.01–0.09%	MIC and 0.1%, 2 h	Significant 1.4–3.3 log reductions of sessile cells when treated with MIC and 0.1%.	Sadekuzzaman et al. (2018)
	Thyme, Oregano, Carvacrol	N/A	0.10–0.50%, 24h	Complete inactivation with 0.25% for 24 h	Desai et al. (2012)
Gram-negative bacteria
E. coli	Eugenol, CINb	1 μg/ml	0.5–2 μg/ml, 0–90 min	Complete inhibition at MIC after 60–75 min	Ali et al. (2005)
	Carvacrol, Thymol	200 mg/l	MIC, 12 h	No complete inhibition but significant reductions	Xu et al. (2008)
	Carvacrol, CIN, Thymol	0.2–0.4 mg/ml	0.01–4 mg/ml, 24h	Significant inhibition at MIC Around 3–5 log reductions with 0.5–1 mg/ml EO	García-Salinas et al. (2018)
	Black pepper	1.0 μl/ml	MIC and 2MIC, 24 h	Significant inhibitory effect of 96.73% after 24 h exposure to 2MIC	Zhang et al. (2017)
	Origanum vulgare L., Rosmarinus officinalis L.	0.6–10 μl/ml	MIC, 24 h	Significant reduction after 2–8 h exposure	de Medeiros Barbosa et al. (2016)
	Thymbra capitata	0.05%	1%, 30–60 s	Inhibition of approximately 8 logs after 30–60 s	Falcó et al. (2019)
E. coli, (Biofilms)	Thymbra capitata	N/A	0.25–2.5%, 1–10 min	Reduction of >3 logs after 10 min exposure to 2.5%	Falcó et al. (2019)
E. coli O157:H7	Carvacrol	N/A	1 mM = 0.015%, overnight	Significant inhibition of flagella synthesis and production of heat shock proteins 60	Burt et al. (2007)
	p-cymene	N/A	1–10 Mm, overnight	No significant activity
	Corydothymus capitatus	0.02%	0.06–0.02%, N/A	At 0.025%, significant effect on murein composition and reduction of intracellular ATP with an increase in extracellular ATP	Caillet et al. (2005); Caillet and Lacroix (2006)
	Mustard	0.2%	0–0.2%, 30 min	At 0.1 and 0.2%, a significant increase in both extracellular ATP and cell constituents' release.	Turgis et al. (2009)
E. coli O157:H7 (Biofilms)	Thyme, Tea tree	0.01–0.09%	MIC and 0.1%, 2 h	Significant 1.4–3.3 log reductions of sessile cells when treated with MIC and 0.1%.	Sadekuzzaman et al. (2018)
Salmonella spp.	Origanum vulgare L., Rosmarinus officinalis L.	0.6–10 μl/ml	MIC, 24 h	Significant reduction after 2–8 h exposure	de Medeiros Barbosa et al. (2016)
	Thymbra capitata	0.05%	1%, 30–60 s	Inhibition of approximately 8 logs after 30–60 s	Falcó et al. (2019)
	Mustard	0.2%	0–0.2%, 30 min	At 0.1 and 0.2%, a significant increase in both extracellular ATP and cell constituents' release.	Turgis et al. (2009)
	Thyme, Oregano, Carvacrol	0.025%	0.006–0.1%, 24 h	Complete inhibition at MIC	Soni et al. (2013)
Salmonella spp. (Biofilms)	Thymbra capitata	N/A	0.25–2.5%, 1–10 min	Around 1 log reduction after 10 min exposure to 2.5%	Falcó et al. (2019)
	Carvacrol, Thymol	156–312 μg/ml	16–624 μg/ml, 1 h	Reduced established biofilms but no complete inhibition	Amaral et al. (2015)
	Thyme, Tea tree	0.01–0.09%	MIC and 0.1%, 2 h	Significant 1.4–3.3 log reductions of sessile cells when treated with MIC and 0.1%.	Sadekuzzaman et al. (2018)
	Thyme, Oregano, Carvacrol	N/A	0.006–0.1%, 24 h	Significant reduction after 1 h exposure to 0.05 or 0.1%	Soni et al. (2013)
	Mentha piperita, Cymbopogon citratus	7.8 μl/ml	MIC, 10–40 min	Significant reductions of 4.03–4.20 logs after 10 min contact and complete inhibition after 20 min	Valeriano et al. (2012)
P. aeruginosa	Origanum compactum	0.031–1%	MIC and 1.5MIC, 0–120 min	Immediately significant reductions at 1-1.5MIC	Bouhdid et al. (2009)
P. aeruginosa (Biofilms)	Carvacrol, Thymol	0.02–0.05%	1/16 –2MIC, 24 h	Inhibited up to 97% at 2MIC	El Abed et al., 2011
Aeromonas spp.	Cymbopogon flexuosus, Thymus vulgaris	0.47–15 mg/ml	MIC, 24 h	Complete inhibition	Quendera et al. (2019)
Aeromonas spp. (Biofilms)	Cymbopogon flexuosus, Thymus vulgaris	N/A	1.9–30 mg/ml, 30 min-1 h	Higher levels of eradication were reported for Aeromonas spp. at 15 and 30 mg/ml for all treatment times	Quendera et al. (2019)
	Thymus vulgaris, Cymbopogon citratus	31–62 μl/ml	MIC, 15 min	Significant reduction of 3.84–4.51 log CFU/cm2	Millezi et al. (2013)
Fungi
C. albicans	Cymbopogon winterianus, Cinnamon cassia	65.5–250 μg/ml	7.8–1000 μg/ml, 24–48 h	Complete inhibition at MIC	Almeida et al. (2016)
C. albicans (Biofilms)		N/A	1 mg/ml,0–48 h	Significant reductions but no complete inhibition and no prevention of biofilm regrowth
	Thymol	125 μg/ml	1/8MIC-MIC, up to 24 h	Significant reductions at MIC after 1 h and almost a complete destruction of 3D structure	Braga et al. (2008)

^aMIC: Minimum Inhibitory Concentration.

^bCIN: Cinnamaldehyde.