In vitro antimicrobial activity of less-utilized spice and herb extracts against selected food-borne bacteria

In this study we compared the antimicrobial activities of extracts from four under-utilized spices and herbs including goraka (Garcinia quaesita), galangal (Alpinia galanga), lemon iron bark (Eucalyptus staigerana) and mountain pepper (Tasmannia lanceolata) to the three common spices and herbs pepper (Piper nigrum), rosemary (Rosmarinus officinalis), and oregano (Oreganum vulgare). Different extraction solvents were used (water, ethanol and hexane) and extracts were tested against four food-borne bacteria (Escherichia coli, Salmonella Typhimurium, Listeria monocytogenes and Staphylococcus aureus) using agar disc diffusion and broth dilution assays. Solvent type greatly influenced the antimicrobial activity of the spice and herb extracts except for those of P. nigrum, which had little or no activity. In general the spice and herb extracts with antimicrobial activity were more effective against Gram-positive than Gram-negative bacteria. Extracts from the under-utilized herbs and spices had significant activity. In particular, A. galanga hexane and ethanol extracts and E. staigerana ethanol and water extracts had strong antimicrobial activity against S. aureus and/or L. monocytogenes. Interestingly the minimal inhibitory concentrations determined using the broth dilution method and the diameter of inhibition zones using the disc diffusion assay were not strongly correlated (r² ranged from 0.10 to 0.70) in most extracts, suggesting that choosing just one method for antimicrobial testing may lead to indefinite conclusions. The total phenolic content of two extracts from each spice and herb was assayed to establish any relationship between antimicrobial activity and phenolic compound levels, however this was found to poorly correlated (r² < 0.30). This study has demonstrated that simple extracts of novel under-utilized herbs and spices have potential antimicrobial activity against food-borne bacterial species. Further it is indicated that the antimicrobial activity in some herbs and spices may be due to the presence of substances other than phenolic compounds.     

Assessment of antibacterial activity of fractions from burdock leaf against food-related bacteria

The chemical composition and antibacterial activities of burdock leaves fractions against six food-related bacteria (Staphylococcus aureus, Streptococcus pneumoniae, Bacillus subtilis, Escherichia coli, Shigella dysenteriae and Salmonella typhimurium) were first investigated. The burdock leaves extract was fractioned with ethyl acetate, n-butanol and water, named as EF, BF and WF. The data from minimum inhibitory concentration (MIC) values showed that EF and other fractions effectively inhibited the growth of all test bacterial pathogens, the antibacterial activity of EF being much greater than BF and WF. The time–kill study indicated that EF exhibited significant bactericidal activity against all the six pathogens. At 12 h, EF was bactericidal for 4/6, 6/6 and 6/6 strains at 1× MIC, 3× MIC and 5× MIC, respectively. For all the fractions, the antibacterial capacity had a significant correlation with total phenolic content, suggesting that the activities were probably due to the combined action of phenolic compounds. The phenolic compounds of the fractions were then identified for the first time. After activity-guide fractionation and separation by flash chromatogram, two purified active compounds (chlorogenic acid, rutin) were obtained, and identified by UPLC–MS/MS. The ethyl acetate fraction based on its lower MIC values, concentration and time-dependent antibacterial and bactericidal activities could be useful in control of foodborne bacterial pathogens.     

Antibacterial activity and mechanism of pinoresinol from Cinnamomum Camphora leaves against food-related bacteria

Pinoresinol from the leaves of Cinnamomum camphora used as a model natural compound was extracted and isolated. The chemical characterization of the compound was confirmed using UV, IR, MS, H NMR and C HMR. The purity of the compound (86%) was determined using HPLC technique and it was used for further experiments. Its antibacterial activities against five food-related bacteria (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, Salmonella enterica) were detected using both broth dilution method and disk diffusion method. Results indicated that 62.5 μg/mL pinoresinol completely inhibit the growth of five bacteria. Much effort was focused on elucidating the mechanism of antibacterial action of pinoresinol against P. aeruginosa and B. subtilis by determination of cell permeability and observing the changes of cell microstructure using scanning electron microscope (SEM). The leakage of the soluble saccharides and proteins were detected and up to 13.89 and 21.76 μg/mL, respectively for P. aeruginosa and 11.08 and 19.05 μg/mL, respectively for B. subtilis. Measurements of the release of the soluble saccharides and proteins confirmed the disruptive action of pinoresinol on cytoplasmic membrane. The damages of the pinoresinol on cell wall were confirmed using Gram staining and scanning electron microscopy (SEM). We concluded that the antibacterial action mechanism of the pinoresinol is attributed to the physiological and morphological changes in bacterial cells.     

In vitro antibacterial activity of Australian native herb extracts against food-related bacteria

The antibacterial activities of water, ethanol and hexane extracts of five Australian herbs (Backhousia citriodora, Anetholea anisata, Eucalyptus staigerana, Eu. olida and Prostanthera incisa) against seven food-related bacteria (Enterococcus faecalis, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella Enteritidis, Sal. Typhimurium and Staphylococcus aureus) were determined by the microtitre broth microdilution assay. The water extracts of all the herbs displayed no or low antimicrobial activity against all of the bacteria tested with the exception of S. aureus. Relatively high levels of activity (minimum inhibitory concentrations of 125–15.6 μg ml⁻¹) against this pathogen were present in water extracts from all herbs except P. incisa. The ethanol and hexane extracts of all herbs displayed some activity against a number of the bacteria tested, with no one particular herb displaying an obviously higher level or range of activity. Staphylococcus aureus proved to be the most sensitive of the bacteria tested against the solvent extracts with all extracts displaying activity ranging from 125 to 7.8 μg ml⁻¹, while E. coli and L. monocytogenes, on the other hand, proved the least sensitive with only five of 15 herb/extract combinations displaying any activity against these pathogens. The extracts of the Australian native herbs examined in this study have potential for application in foods to increase shelf-life or promote safety.     

Antimicrobial activity of natural antimicrobial substances against spoilage bacteria isolated from fresh produce

The aim of this study was to investigate the efficacy of natural antimicrobial substances for inhibiting vegetable spoilage bacteria. Natural antimicrobial compounds (carvacrol, thymol, eugenol, cinnamic acid, nisin, and chitosan), organic acids (acetic acid and lactic acid), and chemical sanitizers (sodium hypochlorite and chlorine dioxide) were evaluated for their antibacterial activities, as single and combination treatments, against 15 spoilage bacteria isolated from vegetables, using the agar disc diffusion and broth dilution methods. Carvacrol, thymol, and eugenol showed strong inhibitory effects compared to those of the other antimicrobial substances, and their average minimum inhibitory concentration (MIC) values against 15 spoilage bacteria were 167, 648, and 168 μg/ml, respectively. When they were combined, four kinds (carvacrol + thymol, carvacrol + eugenol, thymol + eugenol, and carvarol + thymol + eugenol) of the combination formulas showed higher antibacterial effect than others against spoilage bacteria, with average MIC values of 47, 43, 59, and 42 μg/ml, respectively. However, two combinations (carvacrol + thymol, and carvacrol + thymol + eugenol) showed the strongest inhibitory effects against bacteria in fresh vegetables among all treatments. These results could be used for the development of new sanitation or preservation methods to improve freshness and to extend the shelf-life of fresh produce.     

Essential oils composition,antioxidant and antimicrobial activity of the leaves and flowers of Chaerophyllum macropodum Boiss

This study reports the essential oils chemical composition and in vitro antioxidant and antimicrobial potentials of the leaves and flowers of Chaerophyllum macropodum. GC and GC/MS analysis of the plant essential oils led to the identification of 49 components making 98.3–99.4% of its oils. The main constituents of the essential oils were trans-β-farnesene, trans-β-ocimene, β-pinene, limonene, spathulenol and myrcene constituting 49.6–73.1% of the oils. The extracts from the leaves and flowers showed moderate antioxidant activities in 1,1-diphenyl-2-picrylhydrazyl (DPPH) test (IC₅₀ values = 196.8 and 167.1 μg/ml respectively) and β-carotene/linoleic acid assay (inhibitions percentages = 69.9% and 62.7% respectively), but the essential oils were almost inactive in these tests. On the other hand, only the essential oils of the plant showed considerable antimicrobial activity against most of the tested microorganisms.     

Antimicrobial activity of lacticin 3147 against oenological lactic acid bacteria. Combined effect with other antimicrobial agents

This study investigated the potential use of lacticin 3147 to control growth of wine lactic acid bacteria (LAB) aiming to develop new approaches for reducing the content of sulphites in wine. Lacticin 3147, potassium metabisulphite and eucalyptus extract interactions were also evaluated. Inhibitory activity of the bacteriocin demonstrated to be strain-dependent and the highest antimicrobial effect was established at the exponential growth phase. Low lacticin 3147 IC₅₀ values (10.46–57.97 UA/mL) were measured for most of the strains, except for Lactobacillus casei CIAL-51 which were remarkably resistant (IC₅₀ = 141.70 UA/mL); Oenococcus oeni CIAL-117 were the most sensitive strain (IC₅₀ = 10.46 UA/mL). A synergistic effect of either lacticin 3147 or eucalyptus extract in combination with metabisulphite in inhibiting LAB growth was measured. Addition of lacticin 3147 to growing cultures of Lactobacillus plantarum CIAL-92 caused effective cell lysis, decrease of cell viability and extensive membrane damage, differing from the effects detected after addition of eucalyptus extract. To our knowledge, this is the first study that reports the inhibitory activity of this bacteriocin against oenological LAB and its potential role in the wine industry. The potential of eucalyptus extract as antimicrobial agent in winemaking is also highlighted. A combination of these two antimicrobials with metabisulphite could represent a promising approach to preserve LAB spoilage in wine and, consequently, eliminate or reduce the addition of SO₂.     

Chemical composition,antibacterial activity and mechanism of action of essential oil from seeds of fennel (Foeniculum vulgare Mill.)

Fennel (Foeniculum vulgare Mill.) is widely cultivated and used as a culinary spice. In this work, the chemical composition of the essential oil obtained by hydrodistillation of fennel seeds was analyzed by gas chromatography-mass spectrometry (GC–MS), and 28 components were identified. Trans-anethole (68.53%) and estragole (10.42%) were found to be the major components. The antibacterial activity, minimum inhibitory concentration (MIC), and minimum bactericide concentration (MBC) of essential oil against several food-borne pathogens were evaluated. The results showed that the gram positive and gram negative strains of bacteria had different sensitivities to essential oil of fennel seeds, the essential oil exhibited antibacterial activity against Staphylococcus albus, Bacillus subtilis, Salmonella typhimurium, Shigella dysenteriae and Escherichia coli according to the results of MIC and MBC. Among these bacteria, S. dysenteriae was the most sensitive to essential oil, showing the lowest MIC and MBC values of 0.125 and 0.25 mg/mL respectively. In addition, kill-time assay also showed that the essential oil had a significant effect on the growth rate of surviving S. dysenteriae. We concluded that the mechanism of action of the essential oil against S. dysenteriae might be described as essential oil acting on membrane integrity according to the results of the leakage of electrolytes, the losses of contents (proteins, reducing sugars and 260 nm absorbing materials) assays and electron microscopy observation.     

Antimicrobial properties of selected essential oils in vapour phase against foodborne bacteria

The aim of this study was to identify antimicrobial properties of essential oils in vapour phase. In vitro antibacterial activity against five foodborne bacteria (Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella enteritidis, Staphylococcus aureus) was evaluated by disc volatilization method. The results were expressed as minimum inhibitory concentrations (MIC) in μl/cm³ of air. Thirteen of the 27 essential oils were active at least against one bacterial strain in the range of tested concentrations (0.0083–0.53 μl/cm³). The best results were shown by Armoracia rusticana (MIC 0.0083 μl/cm³) against all of the strains, followed by Allium sativum > Origanum vulgare > Thymus vulgaris > Satureja montana, Thymus pulegioides > Thymus serpyllum > Origanum majorana > Caryopteris x clandonensis, Hyssopus officinalis, Mentha villosa, Nepeta x faassenii, Ocimum basilicum var. grant verte. In conclusion, certain essential oils are highly effective in vapour phase and could be used in control of foodborne bacterial pathogens.     

Essential oil composition and biological/pharmacological properties of Salmea scandens (L.) DC

Salmea scandens (L.) DC is an indigenous edible plant whose stem bark is traditionally used as food by people of Oaxaca, México. Proximate analysis of the edible stem bark revealed abundant amounts of fiber (43.67%) and protein (9.27%). GC and GC-MS analyses demonstrated that the essential oil from leaves contained high levels of germacrene D (47.1%) and elemol (15.3%), whereas that of the stem bark contained the alkylamides N-Isobutyl-(2E,4E,8Z,10E/Z)-dodecatetraenamide isomers (39.7%). Levels of these compounds in the essential oil from both organs were in similar concentrations in all seasons except winter. The HPLC purified N-Isobutyl-(2E,4E,8Z,10E/Z)-dodecatetraenamide isomers produced a non-competitive inhibition on porcine pancreatic lipase. The enzymatic assays with these compounds revealed a modification on V_max (0.0431–0.0533 mM min⁻¹) whereas the K_m value (0.880–0.881 mM) was not significantly changed. Essential oil from the stem bark showed a high anti-microbial activity against some phytopathogenic microorganisms. The MIC's in μg mL⁻¹ for Pseudomonas syringae pathovars were tabaci 56.1, tomato 91.2 and phaseolitica 196.4, for Clavibacter michiganensis 35.8 and Erwinia carotovora 48.1. The fungi Fusarium oxysporum and Phytophthora infestans had MIC's in μg mL⁻¹ of 3.3 and 2.4 respectively. Same essential oil was highly effective against larvae from Aedes aegypti (LC₅₀ = 0.3 μg mL⁻¹) and Anopheles albimanis (LC₅₀ = 2.5 μg mL⁻¹).     

Chemical composition,antibacterial activity of Cyperus rotundus rhizomes essential oil against Staphylococcus aureus via membrane disruption and apoptosis pathway

The chemical composition, antibacterial activity and mechanism of essential oil from Cyperus rotundus rhizomes against Staphylococcus aureus were investigated in this study. Results showed that α-cyperone, cyperene and α-selinene were the major components of the essential oil. The essential oil exhibited strong antibacterial activity against S. aureus with the minimum inhibitory concentration (MIC) and minimum bactericide concentration (MBC) were 10 and 20 mg/mL respectively, and the antibacterial effects increased with increasing essential oil concentrations and treatment time. The electric conductivity, cell membrane integrity, NPN uptake, and membrane potential assays demonstrated that essential oil disrupted the membrane integrity of S. aureus. Electron microscope observations further confirmed that essential oil destroyed cell membrane. Moreover, we found that essential oil could induce cells death of S. aureus through apoptosis pathway based on apoptosis analysis. These findings suggested that essential oil mainly exerted antibacterial activity by damaging cell membrane and membrane-mediated apoptosis pathway.     

Molecular characterisation and antimicrobial activity of bacteria associated with submerged lactic acid cassava fermentation

Molecular identification of microorganisms associated with submerged cassava fermentation was carried out and isolates of lactic acid bacteria (LAB) were examined for antimicrobial activity, including ability to produce antimicrobial peptides as a first step to define starter cultures for controlled cassava fermentations. A total of 75 isolates, including 41 LAB, 31 aerobic bacteria (AB) and three anaerobic bacteria were isolated from unfermented and fermenting cassava roots, cassava leaves and fermented cassava dough and identified by a combination of phenotypic tests and sequencing of 16S rRNA, rpoA, rpoB and pheS genes. Microbial diversity at interspecies and intraspecies level was screened by, respectively, PCR amplification of the 16S-23S rDNA intergenic transcribed spacer (ITS-PCR) and repetitive sequence based PCR (rep-PCR). Antimicrobial activity of LAB cultures and supernatants against indicator bacteria; Escherichia coli, Salmonella enterica serotype Typhimurium (S. Typhimurium), Bacillus cereus and Staphylococcus aureus was studied using agar diffusion tests. Furthermore, inactivation of indicator bacteria was investigated in both liquid medium and during controlled cassava fermentation. Results revealed a diversity of bacterial genera, species and subspecies associated with submerged cassava fermentation. DNA sequencing enabled identification of LAB isolates as Lactobacillus plantarum, Weissella confusa, Weissella paramesenteroides, Lactobacillus rhamnosus, Lactobacillus hilgardii, Lactobacillus paracasei, Leuconostoc mesenteroides, Enterococcus faecium, Enterococcus casseliflavus, and Pediococcus acidilactici. Lactobacillus spp. were the predominant LAB and were present in all cassava samples studied. Aerobic bacteria were predominantly Bacillus spp., including Bacillus subtilis, Bacillus amyloliquefaciens and B. cereus. Other species identified included Staphylococcus pasteuri and Clostridium beijerinkii. Cells, supernatants and cell free supernatants (CFS) of selected LAB isolates were able to inhibit both Gram positive and Gram negative pathogenic bacteria. LAB isolates inactivated all indicator organisms during controlled cassava fermentations, with a 4–6 log reduction after 48 h fermentation. The antimicrobial effect of the LAB was attributed to acid production.     

Interfacial activity of alkyl hydroxyl sulfobetaine against crude oil

To study the interfacial activities of zwitterionic surfactant against crude oil, four alkyl hydroxyl sulfobetaines were synthesized. The effects of surfactant structure, concentration, salinity of formation water, and crude oil composition on interfacial activities were discussed. It shows that the octadecyl hydroxyl sulfobetaine can achieve ultralow interfacial tension at the concentrations no less than 0.001%, exhibiting a good interfacial activity and a very strong antidilution ability. The salinity of formation water has no obvious effect on lowering the interfacial tension and the polar component in crude oil is very crucial for the production of ultralow interfacial tension. This work is important for enhanced oil recovery.     

Control of bacteria growth on ready-to-eat beef loaves by antimicrobial plastic packaging incorporated with garlic oil

This study was designated to ascertain the effectiveness of low density polyethylene (LDPE) based film incorporated with garlic oil for inhibition of food pathogen on ready-to-eat beef loaves. The blown film extrusion method was employed to produce film samples added with garlic oil in 2, 4, 6 and 8% w/w as well as sample with 0% w/w which served as control throughout the study. Besides, several analyses were also conducted to determine the water vapour barrier properties, thermal stability and bonding interaction of the plastic packaging as influenced by the incorporation of garlic oil. The outcomes of challenge test showed that regardless of the garlic oil amount (2–8% w/w), the antimicrobial plastic packaging was able to reduce the number of Listeria monocytogenes on beef loaves after 3, 6, 9 and 15 days of storage at 4 °C. However, there were insignificant effects on both Escherichia coli and Brochothrix thermosphacta. For water vapour barrier properties, films with higher amount of garlic oil proved to have weaker barrier properties. There was lack of significant difference in the thermal stability for all samples when tested with thermogravimetry analyser. Also, the infrared analysis indicated garlic oil does not change the polymer structure.     

Addition of phytochemical-rich plant extracts mitigate the antimicrobial activity of essential oil/wine mixtures against Escherichia coli O157:H7 but not against Salmonella enterica

Marinades for preparing raw meats for cooking are frequently made of wine and herbs. We simulated several formulations of potential antimicrobial marinades with these components and other food compatible/food derived extracts. Red wine formulations containing essential oils from oregano or thyme, or their primary active components carvacrol and thymol, respectively, and a mixture of plant extract powders from phytochemical-rich apple skin, green tea, and olive, were evaluated for inhibitory activity against the foodborne pathogens Escherichia coli O157:H7 and Salmonella enterica. Red wine alone exhibited low activity, as did the plant extract suspended in the wine. Surprisingly, the high activity of oregano or thyme essential oils in red wine was reduced in E. coli, but not in Salmonella, by addition of the plant extract. This study shows that essential oils in red wine can be an effective antimicrobial in food, however the possibility exists that phytochemicals, added to the treatment solution or natively present in the food itself, could adversely impact the antimicrobial activity and should be addressed with future studies.     

Identification of lactic acid bacteria isolated from Genestoso cheese throughout ripening and study of their antimicrobial activity

The aim of this work was to study the antimicrobial activity of 395 strains of lactic acid bacteria isolated from Genestoso cheese throughout manufacture and ripening. These were: Lactobacillus (137 strains), Lactococcus (125 strains), Leuconostoc (58 strains) and Enterococcus (75 strains). After the extract had been neutralized and treated with catalase to exclude the action of hydrogen peroxide, 13 lactococci, three lactobacilli, three leuconostocs and five enterococci continued to show antimicrobial activity against one or more of the reference varieties used as indicator strains (Enterococcus faecalis CECT 481, Staphylococcus aureus CECT 240, Lactobacillus plantarum CECT 748, Clostridium tyrobutyricum CECT 4011 and Listeria monocytogenes CECT 4031). The 24 strains of lactic acid bacteria showing antimicrobial activity after excluding the action of hydrogen peroxide were identified at species level by genetic methods. The majority of these strains were isolated from the batch ripened in autumn (37.5% of strains) and the batch ripened in spring (29.2% of 15 strains) manufactured by the same cheesemaker and mainly during manufacture and the first days of ripening.     

Antibacterial activity and mechanism of cinnamon essential oil against Escherichia coli and Staphylococcus aureus

Cinnamon essential oil (EO) exhibited effective antibacterial activity against foodborne spoilage and pathogenic bacteria in model systems using Escherichia coli and Staphylococcus. The minimum inhibition concentration (MIC) of cinnamon EO was similar for both bacteria (1.0 mg/ml) while the minimum bactericide concentration (MBC) were 4.0 mg/ml and 2.0 mg/ml for E. coli and Staphylococcus aureus. GC–MS analysis confirmed that cinnamaldehyde was the major constituent in cinnamon EO (92.40%). Much effort was focused on elucidating the mechanism of antibacterial action of cinnamon EO against E. coli and S. aureus by observing the changes of cell microstructure using scanning electron microscope, determination of cell permeability, membrane integrity and membrane potential. After adding cinnamon EO at MIC level, there were obvious changes in the morphology of bacteria cells indicating cell damage. When cinnamon EO were added at MBC levels, the cells were destroyed. Cinnamon EO led to leakage of small electrolytes, causing rapid increase in the electric conductivity of samples at the first few hours. The values for E. coli and S. aureus reached 60% and 79.4% respectively at 7 h. Moreover, the concentration of proteins and nucleic acids in cell suspension also rose with increased cinnamon EO. Bacterial metabolic activity was decreased 3–5 folds as reflected by the results of membrane potential. Overall, S. aureus was more susceptible to cinnamon EO than E. coli.     

Flow cytometric assessment of the antimicrobial activity of essential oils against Listeria monocytogenes

Flow cytometry was applied to assess the antimicrobial activity of oregano, thyme and cinnamon essential oils against Listeria monocytogenes ATCC19114, using combined staining with propidium iodide (PI) for membrane damage evaluation and carboxyfluorescein diacetate (cFDA) for esterase activity detection. The antimicrobial activity of the essential oils was also tested at different NaCl concentrations.Significant differences were observed between plate count results and flow cytometric data, which suggested the presence of a sublethally stressed subpopulation, not able to form colonies on agar plates.Following treatments, flow cytometric assessment clearly discriminated three different subpopulations: viable, dead and injured cells. Cinnamon essential oil exerted a different impact on the cellular subpopulations, with a lower overall activity and a large percentage of cells having minimally damaged membranes. On the contrary, membrane disintegration seemed to be the primary inactivation mechanism of oregano and thyme essential oils.The antimicrobial activity of the essential oils increased with NaCl concentration increase, but higher NaCl concentrations were necessary following treatments with cinnamon essential oil.Our findings suggest differences in the mode of action of cinnamon essential oil against L. monocytogenes, in comparison with thyme and oregano essential oils.     

Antimicrobial potential and chemical composition of Mentha piperita oil in liquid and vapour phase against food spoiling microorganisms

Antimicrobial potential of Mentha piperita oil in liquid and vapour phase against different bacterial strains (Escherichia coli αDH5, Escherichia coli ATCC 25922, Pseudomonas aeruginosa, Pseudomonas fluorescens, Bacillus subtilis and Staphylococcus aureus), fungal strains (Penicillium digitatum, Aspergillus flavus, Aspergillus niger, Mucor spp, and Fusarium oxysporum) and yeasts (Candida albicans and Sacchromyces cerevisiae) was determined by agar dilution method, well diffusion method and disc volatilization method, respectively. Minimum inhibitory concentration (MIC) and Minimum bactericidal and fungicidal concentration (MBC/MFC) of M. piperita oil varied from 1.13 to 2.25 mg/ml and 2.25 to 9 mg/ml for bacterial strains, 1.13 to 2.25 mg/ml and 2.25 to 4.5 mg/ml for fungal strains and 1.13 mg/ml and 2.25 mg/ml for yeasts, respectively. Bacterial inhibition zone due to M. piperita oil (40 μl/well) varied from 13 mm (P. aeruginosa) to 22 mm (B. subtilis). Bacterial inhibition zone due to M. piperita oil (40 μl) vapour varied from 22 mm (P. fluorescens) to 35 mm (B. subtilis) while almost complete growth inhibition occurred in case of fungal strains. In the kill time assays, 100% reduction in viability of C. albicans and B. subtilis was found within 8 h exposure to M. piperita oil vapour. Significant morphological alterations due to the effect of M. piperita oil and oil vapour on B. Subtilis have also been observed by scanning electron microscope.Chemical constituents of the M. piperita essential oil and oil vapour have been identified by gas chromatography (GC), gas chromatography/mass spectrometry (GC–MS) and Solid phase micro extraction-gas chromatography mass spectrometry (SPME GC–MS), respectively.