Antimicrobial activity of binary combinations of natural and synthetic phenolic antioxidants against Enterococcus faecalis

This study investigated the antimicrobial activity of 3 natural (thymol, carvacrol, and gallic acid) and 2 synthetic [butylated hydroxyanisole (BHA) and octyl gallate] phenolic compounds, individually and in binary combinations, on 4 dairy isolates of Enterococcus faecalis with different virulence factors (β-hemolytic, gelatinase, or trypsin activities; acquired resistance to erythromycin or tetracycline; and natural resistance to gentamicin). A checkerboard technique and a microdilution standardized method were used. All compounds individually tested exhibited antimicrobial activity against E. faecalis, with minimal inhibitory concentrations (MIC) ranging from 30 μg/mL (octyl gallate) to 3,150 μg/mL (gallic acid), although no significant differences were detected among strains to each phenolic compound. Carvacrol in combination with thymol or gallic acid, and gallic acid combined with octyl gallate showed partial synergistic inhibition of all E. faecalis strains. The most effective combinations were thymol + carvacrol and gallic acid + octyl gallate, as the MIC for each of these compounds was reduced by 67 to 75% compared with their respective individual MIC. These results highlight the possibility of using combinations of these phenolic compounds to inhibit the growth of potential virulent or spoilage E. faecalis strains by reducing the total amount of additives used in dairy foods.     

Antimicrobial activities of some thymol derivatives from the roots of Inula hupehensis

In a search for some naturally occurring antimicrobial compounds found in medicinal plants, herbs and spice extracts, four thymol derivatives were isolated from the roots of Inula hupehensis (a medicinal plant) and identified as the new compound 9-O-β-d-glucopyranosyl-9-hydroxythymol (1), together with 8,9-epoxy-10-isobutyryloxythymyl isobutyrate (2), 8-hydroxy-9, 10-diisobutyloxythymol (3) and 8,9,10-trihydroxythymol (4). These thymol derivatives, with a semi-synthetic compound 9,10-dihydroxy-8-methoxythymol (5), were tested for their antimicrobial activities against three bacteria and six plant pathogenic fungi. Within the series of thymol derivatives tested, compound 3 was the most active, particularly displaying moderate antibacterial activities against Staphylococcusaureus, Methicillin-resistant S. aureus and Escherichia coli with MICs of 62.3, 62.8, and 250 μg/ml. Moreover, this compound exhibited inhibitory activities against three plant pathogenic fungi: Rhizoctonia solani, Phytophthora melonis and Peronophythora litchi, with EC₅₀ values of 157, 180 and 141 μg/ml. To our knowledge, this is the first report that these five thymol derivatives show inhibitory activity against plant pathogenic fungi.     

Olive glutaraldehyde-like compounds against plant pathogenic bacteria and fungi

Aqueous solutions from table olives constitute a major environmental problem because of their high mineral and organic contamination but they also contain compounds with antimicrobial properties. In this study, the bactericidal and fungicidal activities of salt-free table olive solutions against several phytopathogenic micro-organisms were examined. The storage solutions of black ripe olives showed noticeable bactericidal activity against species of Erwinia, Clavibacter, Agrobacterium and Pseudomonas, although the washing waters from Spanish-style green olives were less effective. In fact, black olive storage solutions diluted to 20–30% were able to reduce the inoculated population of Erwinia amylovora and Pseudomonas syringae up to 6–7 log. This bactericidal activity was correlated with the presence of olive glutaraldehyde-like compounds such as the dialdehydic form of decarboxymethyl elenolic acid in these solutions, either free or linked to hydroxytyrosol. Experiments in vitro demonstrated that the bactericidal activity of these substances could explain most of the activity of the black olive storage solutions. Moreover, these salt-free table olive solutions also showed fungicidal activity against species of Phytophthora, Colletotrichum, Alternaria, Botrytis and Pestalotiopsis. The black olive storage solutions were more fungicidal than the washing solutions from Spanish-style green olives, with mycelial growth inhibition of up to 100% being attained, in some instances. These findings open the possibility of using table olive wastewaters in agriculture for pest management.     

Assessment of antimicrobial activity of coffee brewed in three different ways from different origins

The antimicrobial effect against pathogens such as Staphylococcus aureus, Enterecoccus faecalis, Listeria monocytogenes, Pseudomonas aeruginosa, Escherichia coli and Salmonella choleraesius was determined in four types of coffee (Coffea arabica L. cv. Colombia, decaffeinated cv. Colombia, cv. Ethiopia and cv. Kenya). Coffee was seen to have significant activity against the growth of food spoilage bacteria. Among the Gram-positive bacteria, coffee was strongly active against S. aureus, moderately active against L. monocytogenes and had a slightly inhibitory effect against E. faecalis. However, coffee samples were found to be less active against Gram-negative bacteria. The results show that espresso Colombia coffee has better antimicrobial activity than filter and Italian coffee with significant differences (p?<?0.05). Taking into account the origin, there were significant differences (p?<?0.05) between Kenya and decaffeinated Colombia, on the one hand, and Ethiopia and Colombia coffee, on the other, the two last showing the highest antimicrobial activity. The antimicrobial activity of the coffee from different origins studied in this paper increased with concentration. Typical coffee compounds were also analysed, and only caffeic and chlorogenic acids showed any inhibitory effect against the growth of all the analysed bacteria. The antibacterial properties of coffee means that it has a promising potential as natural food ingredient to extend the shelf life of foods such as cake, cookies or biscuits, coffee flavoured with shakes, yoghurt.     

Green processes based on the extraction with pressurized fluids to obtain potent antimicrobials from Haematococcus pluvialis microalgae

In the present work, the antimicrobial activity of different pressurized liquid extracts obtained from Haematococcus pluvialis microalga was tested against several microorganisms of importance for the food industry (Escherichia coli, Staphylococcus aureus, Candida albicans and Aspergillus niger). Extractions were performed with hexane and ethanol at four different temperatures (50, 100, 150 and 200 °C) for 20 min. The results showed that extracts obtained with both solvents (hexane and ethanol) from the green motile cells of the microalgae (green phase) presented a low antimicrobial activity against all the microorganisms tested. However, the antimicrobial activity of the extracts obtained from the red hematocysts without flagella (red phase) was totally different depending on the solvent used for the extraction. Hexane extracts showed an antimicrobial activity quite similar to that obtained with the green microalgae, while the antimicrobial activity of ethanol extracts was much higher. This fact seems to indicate that compounds related to antimicrobial activity of this microalga are found in higher quantities in the red phase of the microalgae and could be relatively polar compounds. Moreover, ethanol extracts from the red phase obtained at 100 °C presented the highest antimicrobial activity. In order to identify the compounds responsible for the antimicrobial activity, a GC-MS characterization of the extracts obtained with both hexane and ethanol at 100 °C, for Haematococcus pluvialis in the green and red phases was also performed. Therefore, the highest antimicrobial activity of the ethanol extract corresponding to red Haematococcus can be associated with the presence in this extract of short-chain fatty acids, which have been previously described to possess antimicrobial activity.     

The antimicrobial,mechanical, physical and structural properties of chitosan–gallic acid films

Chitosan films incorporated with various concentrations of gallic acid were prepared and investigated for antimicrobial, mechanical, physical and structural properties. Four bacterial strains that commonly contaminate food products were chosen as target bacteria to evaluate the antimicrobial activity of the prepared gallic acid–chitosan films. The incorporation of gallic acid significantly increased the antimicrobial activities of the films against Escherichia coli, Salmonella typhimurium, Listeria innocua and Bacillus subtilis. Chitosan films incorporated with 1.5 g/100 g gallic acid showed the strongest antimicrobial activity. It was also found that tensile strength (TS) of chitosan film was significantly increased when incorporating 0.5 g/100 g gallic acid. Inclusion of 0.5 g/100 g gallic acid also significantly decreased water vapor permeability (WVP) and oxygen permeability (OP). Microstructure of the films was investigated by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) and it was found that gallic acid was dispersed homogenously into the chitosan matrix.     

Development and characterization of antimicrobial poly(l-lactic acid) containing trans-2-hexenal trapped in cyclodextrins

Trans-2-hexenal, a naturally occurring plant volatile with antimicrobial capacity, was encapsulated into β-cyclodextrins (β-CDs), enzymatically modified starch, and shown effective to control main microorganisms causing food spoilage (Alternaria solani, Aspergillus niger, Botrytis cinerea, Colletotrichum acutatum, Penicillium sp). Loaded β-CDs were incorporated into a poly(l-lactic acid) (PLA) matrix by extrusion and casting, and yielded antimicrobial polymers made from natural resources. A masterbatch was used prior to sheet casting to improve the dispersion of the antimicrobial agent in the PLA matrix. However, this increased the number of extrusion processes for the material. The concentration of the antimicrobial compound in the polymers and its antimicrobial capacity against one food spoilage microorganism (A. solani) were measured during the different processing operations. Although the concentration of trans-2-hexenal was reduced by processing by about 70 and 99% compared to the loaded β-CDs, for the masterbatch and sheet, respectively, the polymers were still effective in reducing microbial growth. The changes of the polymer properties due to the addition of the antimicrobial agent were investigated, too. It was found that the mechanical and barrier properties of the PLA were changed (decreased by about half the tensile strength and elongation at break and nine-fold increased permeability) while the physical properties remained the same. Based on these results, the developed polymer may be a viable antimicrobial material for applications in food packaging.     

Combinations of food antimicrobials at low levels to inhibit the growth of Salmonella sv. Typhimurium: a synergistic effect?

The use of many antimicrobial compounds in combination can achieve a good microbiological safety in food while decreasing the doses of each compound in the product. This is interesting in terms of consumer demand. In that context, combinations of five aromatic compounds (thymol, carvacrol, citral, eugenol, geraniol) and four acidic compounds (acetic acid, citric acid, lactic acid, pyropolyphosphoric acid) were investigated for their ability to inhibit the growth of Salmonella sv. Typhimurium. Many combinations of either acidic or aromatic compounds appear to be promising. Some antimicrobials, like citric acid or thymol, lead to a better amplification of inhibition than others, but no real synergistic effect has been demonstrated between compounds. Moreover, our results underline that it is important to take into account the cumulative effect of each compound when compounds are mixed.     

3‐Hydroxypyridinone‐l‐phenylalanine conjugates with antimicrobial and tyrosinase inhibitory activities as potential shrimp preservatives

To explore the potential of novel tyrosinase inhibitors, 3‐hydroxypyridinone‐l ‐phenylalanine conjugates, as shrimp preservatives, compounds 1 and 2 were evaluated for the antimicrobial activity, and compound 2 was investigated for the shrimp preservative efficacy. It was found that they both possess a stronger antibacterial effect than kojic acid against two Gram‐positive bacteria and three Gram‐negative bacteria. The minimum inhibitory concentrations (MICs) of compound 2 against Escherichia coli, Staphylococcous aureus, Salmonella gallinarum, Vibrio parahaemolyticus and Bacillus subtilis were determined as 18.5, 37, 148, 37 and 295 μg mL^?1, respectively, whereas MICs of kojic acid against the same 5 bacterial strains were determined to be 355, 178, 1420, 1420 and 355 μg mL^?1, respectively. It has also been demonstrated that treatment with compound 2 improves the sensory properties, retards the growth of spoilage bacteria, decreases the total volatile basic nitrogen (TVB‐N) and increases the pH of Penaeus vannamei Boone, thereby extending the shelf life to 10 days. In contrast, the shelf life of shrimp treated with kojic acid and the control group was 7 and 6 days, respectively. Clearly, 3‐hydroxypyridinone‐l ‐phenylalanine conjugates could find application as shrimp preservatives by inhibiting melanosis and by preventing the growth of bacteria during the storage.     

Study on chemical composition and biological activities of essential oil and extract from Salvia pisidica

In this study, total contents of phenolic, flavanol and flavonol, antioxidant activities and antimicrobial activities of the Turkish endemic Salvia pisidica Boiss. & Heldr. ex Bentham (Lamiaceae) extract and essential oil were assessed in vitro. Total phenolic, flavanol and flavonol contents in the extract were 54.57 mg gallic acid equivalents (GAE)/g, 16.70 mg catechine equivalents (CE)/g and 18.19 mg rutin equivalents (RE)/g, respectively. Antioxidant activities (IC₅₀ value) of the extract and essential oil were determined as 4.88 and 6.41 mg/mL by DPPH assay, respectively. 31 compounds were determined in the essential oil using GC-MS and the major compounds (%) were camphor (23.76), sabinol (19.2), α-thujone (14.2) and eucalyptol (1.8-cineole) (5.8).The antimicrobial activity of the methanolic extract and the essential oil against 13 bacterial and two yeast strains was determined. The extract (concentration 5 g/100 ml or 10 g/100 ml) was effective against most of the strains tested, yet not against Bacillus cereus, Staphylococcus aureus, Aeromonas hydrophila and the two yeast strains tested. The essential oil (2 g/100 ml) showed an antimicrobial effect against all the gram (+) bacteria tested, against Saccharomyces cerevisiae, but was not effective against all gram (−) bacteria and Candida albicans. These results show that S.piscidica essential oil and extract could be considered as a natural alternative to traditional food preservatives and be used to enhance food safety and shelf life.     

Effects of Combined Antimicrobial Agents on Fermentation Initiation by Saccharomyces cerevisiae in a Model Broth System

Effects of sodium benzoate, potassium sorbate, sodium metabisulfite (SO₂), butyl p-hydtoxybenzoic acid and their dual combinations were observed against the ability of the wine yeast, Saccharomyces cerevisiae, Montrachet 522, to begin a fermentation in yeast nitrogen base-glucose broth at pH 3.30. Antimicrobial activities of equal molar concentrations of compounds and combinations of compounds were compared. Butylparaben and combinations involving butylparaben most effectively inhibited fermentation initiation. Combinations involving SO₂ had lower antimicrobial activities than either SO₂ or the other individual compound alone indicating antagonistic effects between SO₂ and the other antimicrobial agents tested. Apparent additive antimicrobial effects were observed for butylparaben/sorbate, butylparaben/ benzoate and benzoate/sorbate.     

Gelatine based films added with bacteriocins and a flavonoid ester active against food-borne pathogens

Active films, based on food grade gelatine added with bacteriocins and/or the flavonoid ester prunin laurate as antimicrobial compounds, were prepared. The films were characterized by water vapor permeability, mechanical property measurements and scanning electron microscopy. Film antibacterial activity was determined by the agar diffusion and direct contact microplate techniques against Listeria monocytogenes 01/155, Staphylococcus aureus ATCC29213 and Bacillus cereus 1. Physical properties of gelatine films were not significantly affected by active compound incorporation. Antibacterial effect on each strain was dependent on the active compound incorporated into the film, but in all cases a synergistic inhibitory action was observed when both antimicrobial compounds were added. Thus, the results of this study suggest that gelatine based active films here presented could provide an alternative strategy for food biopreservation.Industrial relevanceThis work proposes the elaboration of active films based on food grade gelatine and the addition of enterocins A, B and P synthesized by Enterococcus faecium SM21 and the flavonoid ester, prunin laurate, as antimicrobial active compounds. Films were prepared using a simple and low cost methodology and their application can be adapted to different kinds of food systems. The inclusion of the antimicrobial compounds on the film matrix did not alter their functional properties. The obtained films were active against L. monocytogenes, S. aureus and B. cereus, providing an alternative tool for food preservation, especially in the case of foods susceptible to contamination by these pathogens. Although the inhibitory effect of active films was different for each indicator strain, in all cases a synergistic inhibition effect was observed when both active compounds, ES and PL, were added to gelatine films. This synergistic effect between both antimicrobial compounds offers a novel potential hurdle technology for food preservation.     

Brettanomyces susceptibility to antimicrobial agents used in winemaking: in vitro and practical approaches

Brettanomyces bruxellensis is a spoiling yeast responsible for developing off-odors in wine described as “Brett-character.” The objective of this study was to evaluate the antimicrobial activity of four enological compounds against Brettanomyces: potassium metabisulfite (PMB), chitosan, enological tannins and dimethyl dicarbonate. Minimal inhibitory concentrations and minimal biocidal concentrations of the antimicrobial agents were determined, and a comparative study between B. bruxellensis and Saccharomyces cerevisiae was performed under in vitro controlled conditions. All tested compounds showed inhibitory effect on the growth of Brettanomyces. Chitosan and the enological tannins showed selectivity against Brettanomyces, and PMB showed the highest efficacy in concentrations under the currently permitted limits for enological use; consequently, PMB was further evaluated in red wines naturally contaminated by Brettanomyces. Volatile phenol concentrations were determined after long-term storage of the wines treated with PMB. A direct correlation was demonstrated between the concentrations of 4-ethylphenol, 4-ethylguaiacol, 4-propylguaiacol and Brettanomyces populations in the studied wines, and these parameters correlated inversely with the concentrations of PMB employed. This is the first time that 4-propylguaiacol is shown to correlate with Brettanomyces population in wine. It is of enological significance that a concentration of 100 mg/L of total PMB efficiently prevented Brettanomyces growth in the aging red wines of our study and that volatile phenol concentrations were significantly (p < 0.05) higher in those poorly protected wines.     

Antimicrobial activity in the vapour phase of a combination of cinnamon and clove essential oils

The antimicrobial activity of the vapour generated by a combination of cinnamon and clove essential oils against the growth of four Gram-negative (Escherichia coli, Yersinia enterocolitica, Pseudomonas aeruoginosa and Salmonella choleraesuis) and four Gram-positive bacteria (Staphylococcus aureus, Listeria monocytogenes, Bacillus cereus and Enterococcus faecalis) was assessed by means of the fractional inhibitory concentration index (FIC) of the mixture. The presence of synergism or antagonism effects depended on the reference parameter used to estimate such an index. If the minimal inhibitory concentrations were applied, the vapours of the combination of essential oils exerted an antagonistic effect on the growth of E. coli, while they wielded a synergistic effect for the inhibition of L. monocytogenes, B. cereus and Y. enterocolitica when the concentrations of maximal inhibition were used. This fact revealed a clear concentration-dependent interaction.     

Phenolic compounds from the edible seeds extract of Chinese Mei (Prunus mume Sieb. et Zucc) and their antimicrobial activity

Prunus mume seeds have been used as a healthy food and traditional drug in China. The present study investigated the phenolic compounds and antimicrobial activity of ethanolic extract from seeds of P. mume. Total phenolic content was determined as gallic acid equivalents by the Folin-Ciocalteu method. The antibacterial activity was measured by a filter paper disc method. Three chlorogenic acid isomers, namely, 3-O-caffeoylquinic acid, 5-O-caffeoylquinic acid and 4-O-caffeoylquinic acid, were identified from P. mume seeds for the first time. The contents of these isolated compounds were quantified by HPLC. Results showed that 3-O-caffeoylquinic acid was of the highest level in these three isomers. The ethanolic extract exhibited inhibition activity against bacteria and fungi obviously. The isolated phenolic compounds also exhibited inhibition activity against bacteria significantly, but showed weak or no inhibition activity against yeasts and mold. The results exhibited that the antimicrobial activity of P. mume seeds may be partly due to the phenolic compounds.     

Effectiveness of antimicrobial coated oriented polypropylene/polyethylene films in sprout packaging

This study focused on the effect of antimicrobial incorporated soy protein isolate (SPI) coated oriented polypropylene/polyethylene (OPP/PE) packaging on extended shelf life of fresh sprouts. To develop antimicrobial SPI-coated packages, the minimum inhibitory and bactericidal concentrations of antimicrobial (allyl isothiocyanate, trans-cinnamaldehyde, garlic oil, and rosemary oil) and film properties of antimicrobial incorporated SPI films were investigated. Different concentrations (0.6–1.2%, v/v) of the SPI incorporated antimicrobial compounds were coated onto the OPP/PE film and heat-sealed. Packages containing sprouts (alfalfa, broccoli, and radish) were stored at 10 °C for 5 days. Significant reduction of the total microbial count of sprouts was observed in treated samples. Allyl isothiocyanate was the most effective antimicrobial compound, followed by garlic oil and trans-cinnamaldehyde.     

Study of the inhibitory activity of phenolic compounds found in olive products and their degradation by Lactobacillus plantarum strains

Lactobacillus plantarum is the main species responsible for the spontaneous fermentation of Spanish-style green olives. Olives and virgin oil provide a rich source of phenolic compounds. This study was designed to evaluate inhibitory growth activities of nine olive phenolic compounds against four L. plantarum strains isolated from different sources, and to explore the L. plantarum metabolic activities against these phenolic compounds. None of the nine compounds assayed (oleuropein, hydroxytyrosol, tyrosol, as well as vanillic, p-hydroxybenzoic, sinapic, syringic, protocatechuic and cinnamic acids) inhibited L. plantarum growth at the concentration found in olive products. Oleuropein and tyrosol concentrations higher than 100 mM were needed to inhibit L. plantarum growth. On the other hand, sinapic and syringic acid showed the highest inhibitory activity since concentrations ranging from 12.5 to 50 mM inhibited L. plantarum growth in all the strains analyzed. Among the nine compounds assayed, only oleuropein and protocatechuic acid were metabolized by L. plantarum strains grown in the presence of these compounds. Oleuropein was metabolized mainly to hydroxytyrosol, while protocatechuic acid was decarboxylated to catechol. Metabolism of oleuropein was carried out by inducible enzymes since a cell-free extract from a culture grown in the absence of oleuropein was unable to metabolize it. Independent of their isolation source, the four L. plantarum strains analysed showed similar behaviour in relation to the inhibitory activity of phenolic compounds, as well as their ability to metabolize these compounds.     

Chemical analysis of edible aromatic plants growing in Tanzania

The volatiles from the aerial parts of edible plants growing in Tanzania, Leucas glabrata, Plectranthus laxiflorus, Salvia nilotica and Vernonia smithiana, were investigated by GC and GC/MS. Thirty-five compounds were identified from L. glabrata, representing 80.4% of the total oil; forty-three from P. laxiflorus (86.7%); twenty-four from S. nilotica (94.3%); and thirty-nine compounds from V. smithiana (92.9%). Among the identified components, menthone, (p + o)-cymene, trans-caryophyllene and caryophyllene oxide were found as the main ones. Furthermore, the essential oils were investigated for their antimicrobial activity as well as for their antiradical activity, through the DPPH method. Upon antimicrobial assays, the oil of V. smithiana showed very strong antimicrobial activity against Gram-positive bacteria, oral pathogens and pathogenic fungi; the oil of P. laxiflorus also exhibited strong activity, mostly against Gram-positive bacteria and especially oral pathogens, while L. glabrata showed strong activity against all assayed bacteria. The essential oil of S. nilotica appeared to have the most antioxidant activity but was almost inactive against all tested microorganisms.     

Polyphenolic profile,antioxidant properties and antimicrobial activity of grape skin extracts of 14 Vitis vinifera varieties grown in Dalmatia (Croatia)

The aim of the present study was to determine polyphenolic composition, related antioxidative and antimicrobial properties of grape skin extracts from 14 grape varieties (seven white and seven red grape) grown in Dalmatia (Croatia). The content of total phenols, flavonoids, catechins, flavanols and individual polyphenols ((+)-catechin, (−)-epicatechin, epicatechin gallate, procyanidin B1 and procyanidin B2, quercetin glucoside, resveratrol monomers, piceid and astringin) was variety dependent. Antioxidant properties were determined as DPPH radical-scavenging ability (IC₅₀), ferric reducing/antioxidant power (FRAP), Fe²⁺-chelating activity (IC₅₀), and using β-carotene bleaching assay. The high antioxidant capacity of all extracts, both red and white, has been observed and related to the relative amounts of polyphenolic compounds with good antioxidant properties. The antimicrobial activity was screened by broth microdilution test using Gram-positive (Staphylococcus aureus, Bacillus cereus) and Gram-negative bacteria (Escherichia coli O157:H7, Salmonella Infantis, Campylobacter coli). It was confirmed against all tested organisms. Minimum inhibitory concentrations (MICs), were found in the range 0.014–0.59 mg of gallic acid equivalents (GAE)/ml, with lower MICs of white cultivars, especially against Campylobacter and Salmonella.     

Chemical composition and antimicrobial properties of essential oils of three Australian Eucalyptus species

The chemical composition and antimicrobial properties of the essential oils of three common Australian Eucalyptus species, namely E. olida, E. staigeriana and E. dives were determined by gas chromatography/mass spectrometry and the agar disc diffusion method, respectively. A total of 24 compounds were identified from the essential oil of E. dives, with the dominant compounds being piperitone (40.5%), α-phellandrene (17.4%), p-cymene (8.5%) and terpin-4-ol (4.7%). For E. staigeriana, 29 compounds were identified with 1,8-cineole (34.8%), neral (10.8%), geranial (10.8%), α-phellandrene (8.8%) and methyl geranate (5.2%) being the dominant ones. In contrast, a single compound, (E)-methyl cinnamate, accounted for 99.4% of the essential oils of E. oilda, although 20 compounds were identified. The essential oils displayed a variable degree of antimicrobial activity with E. staigeriana oil showing the highest activity. In general, Gram-positive bacteria were found to be more sensitive to the essential oils than Gram-negative bacteria. Staphylococcus aureus was the most sensitive strain while Pseudomonas aeruginosa was the most resistant.