Ubericin K, a New Pore-Forming Bacteriocin Targeting mannose-PTS.

Bovine mastitis infection in dairy cattle is a significant economic burden for the dairy industry globally. To reduce the use of antibiotics in treatment of clinical mastitis, new alternative treatment options are needed. Antimicrobial peptides from bacteria, also known as bacteriocins, are potential alternatives for combating mastitis pathogens. In search of novel bacteriocins against mastitis pathogens, we screened samples of Norwegian bovine raw milk and found a Streptococcus uberis strain with potent antimicrobial activity toward Enterococcus, Streptococcus, Listeria, and Lactococcus. Whole-genome sequencing of the strain revealed a multibacteriocin gene cluster encoding one class IIb bacteriocin, two class IId bacteriocins, in addition to a three-component regulatory system and a dedicated ABC transporter. Isolation and purification of the antimicrobial activity from culture supernatants resulted in the detection of a 6.3-kDa mass peak by matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry, a mass corresponding to the predicted size of one of the class IId bacteriocins. The identification of this bacteriocin, called ubericin K, was further confirmed by in vitro protein synthesis, which showed the same inhibitory spectrum as the purified antimicrobial compound. Ubericin K shows highest sequence similarity to the class IId bacteriocins bovicin 255, lactococcin A, and garvieacin Q. We found that ubericin K uses the sugar transporter mannose phosphotransferase (PTS) as a target receptor. Further, by using the pHlourin sensor system to detect intracellular pH changes due to leakage across the membrane, ubericin K was shown to be a pore former, killing target cells by membrane disruption. IMPORTANCE Bacterial infections in dairy cows are a major burden to farmers worldwide because infected cows require expensive treatments and produce less milk. Today, infected cows are treated with antibiotics, a practice that is becoming less effective due to antibiotic resistance. Compounds other than antibiotics also exist that kill bacteria causing infections in cows; these compounds, known as bacteriocins, are natural products produced by other bacteria in the environment. In this work, we discover a new bacteriocin that we call ubericin K, which kills several species of bacteria known to cause infections in dairy cows. We also use in vitro synthesis as a novel method for rapidly characterizing bacteriocins directly from genomic data, which could be useful for other researchers. We believe that ubericin K and the methods described in this work will aid in the transition away from antibiotics in the dairy industry.

Combined Antimicrobial Effect of Bio-Waste Olive Leaf Extract and Remote Cold Atmospheric Plasma Effluent.

A novel strategy involving Olive Leaf Extract (OLE) and Cold Atmospheric Plasma (CAP) was developed as a green antimicrobial treatment. Specifically, we reported a preliminary investigation on the combined use of OLE + CAP against three pathogens, chosen to represent medical and food industries (i.e., E. coli, S. aureus and L. innocua). The results indicated that a concentration of 100 mg/mL (total polyphenols) in OLE can exert an antimicrobial activity, but still insufficient for a total bacterial inactivation. By using plain OLE, we significantly reduced the growth of Gram positive S. aureus and L. innocua, but not Gram-negative E. coli. Instead, we demonstrated a remarkable decontamination effect of OLE + CAP in E. coli, S. aureus and L. innocua samples after 6 h. This effect was optimally maintained up to 24 h in S. aureus strain. E. coli and L. innocua grew again in 24 h. In the latter strain, OLE alone was most effective to significantly reduce bacterial growth. By further adjusting the parameters of OLE + CAP technology, e.g., OLE amount and CAP exposure, it could be possible to prolong the initial powerful decontamination over a longer time. Since OLE derives from a bio-waste and CAP is a non-thermal technology based on ionized air, we propose OLE + CAP as a potential green platform for bacterial decontamination. As a combination, OLE and CAP can lead to better antimicrobial activity than individually and may replace or complement conventional thermal procedures in food and biomedical industries.

Sodium alginate-based edible coating containing nanoemulsion of Citrus sinensis essential oil eradicates planktonic and sessile cells of food-borne pathogens and increased quality attributes of tomatoes.

There is a growing interest from the worldwide scientific community in formulating edible- biodegradable coatings to replace non-biodegradable and expensive commercial wax-based coatings for preserving postharvest quality attributes of vegetables including tomatoes. Postharvest tomatoes are a suspected vehicle for both Salmonella and Listeria in food poisoning incidents. In this work, the effectiveness of edible nano-emulsion coatings containing sweet orange essential oil and sodium alginate were prepared and characterized, then evaluated antibacterial and antibiofilm activity against Salmonella and Listeria and simultaneously, examined its coating effect on various quality characteristics of tomatoes at 22 ± 2 °C over a 15 days storage period. DLS (Dynamic light scattering) study revealed stable nanoemulsion formulation with 43.23 nm particle size. The high whiteness index of nanoemulsion has a positive impact on product marketability and desirability. Antibacterial and antibiofilm studies revealed nanoemulsion effectively eradicate both sessile and planktonic forms of Salmonella and Listeria in both single and multi-species culture conditions. Tomatoes coated with edible coating significantly enhanced firmness up to 33%, decreased total mesophilic bacteria including Salmonella and Listeria, and reduced weight loss up to 3 fold lower than uncoated one. Sensory analysis revealed that the use of the edible coating increased the total acceptance scores of tomatoes.

Antioxidant and antimicrobial evaluation of rice bran (Oryza sativa L.) extracts in a mayonnaise-type emulsion.

The objective of this study was to evaluate the in vitro antimicrobial and antioxidant activities of different bran extracts and concentrations, and their influence on the parameters of a mayonnaise-type emulsion. To that end, first ethanol and then water were used to extract two rice bran extracts (RBE) from rice bran. Both these extracts were then added at two different concentrations (0.5 and 2%) to the emulsions that were subsequently analysed after seven days under two different storage temperatures, 4 °C and 20 °C. The antioxidant and antimicrobial ability of the extracts were evaluated, along with a control and a synthetic antioxidant. Results indicate the positive effect of rice bran extracts as additives in the food matrix. Ethanolic rice bran extract (EE) at 2% decreased the oxidation as well as mould and yeast proliferation and preserved the emulsion structure, while the other treatments acted in a similar way although their effect was less pronounced.

Effect of drying and interfacial membrane composition on the antimicrobial activity of emulsified citral.

Citral-in-water emulsions were prepared with two different essential oil concentrations of 2.5 and 5.0% (w/w), then spray-dried in the presence of the same amount of maltodextrins (20%). The microcapsules were prepared with two different emulsifier compositions: monolayer microcapsules (ML) stabilized by sodium caseinate alone and layer-by-layer microcapsules (LBL) stabilized by sodium caseinate and pectin. The encapsulation efficiency was higher for LBL microcapsules (e.g. 99.6 ±â€¯0.4% for 2.5% citral) than that for ML ones (e.g. 78.6 ±â€¯0.6% for 2.5% citral) which confirm that the additional pectin layer was able to protect citral during the spray-drying process whatever citral concentration. Furthermore, our results showed that the antibacterial activity of the obtained microcapsules significantly depends on both citral concentration and interfacial membrane composition. The presence of two layers surrounding the citral droplets may result in a progressive and controlled release of the encapsulated citral.

Encapsulation of eugenol by spray-drying using whey protein isolate or lecithin: Release kinetics, antioxidant and antimicrobial properties.

The encapsulation of eugenol (E) by spray-drying using whey protein (WP) or soy lecithin (LE) and maltodextrin in combination with oleic acid (OA) and chitosan (CH) was analysed in order to obtain antioxidant and antimicrobial powders for food applications. Formulations with only WP or LE showed higher encapsulation efficiencies (EE) (95-98%) and antibacterial effect against E. coli and L. innocua due to their greater E load. Incorporation of OA or CH promoted lower EE, which negatively affected the antimicrobial and antioxidant activities of the powders. Furthermore, the addition of CH implied less thermal protection against the E losses. The eugenol release was not notably affected by pH or polarity of the food simulant, but the release rate significantly decreased when incorporating OA and CH. The E-LE formulations better retained the eugenol than E-WP powders when heated above 200 °C, this being relevant for the powder inclusion in thermally treated products.

Antioxidant starch films containing sunflower hull extracts.

This study explores the preparation of antioxidant starch food packaging materials by the incorporation of valuable phenolic compounds extracted from sunflower hulls, which are an abundant by-product from food industry. The phenolic compounds were extracted with aqueous methanol and embedded into starch films. Their effect on starch films was investigated in terms of antioxidant activity, optical, thermal, mechanical, barrier properties and changes in starch molecular structure. The starch molecular structure was affected during thermal processing resulting in a decrease in molar mass, smaller amylopectin molecules and shorter amylose branches. Already 1-2% of extracts were sufficient to produce starch films with high antioxidant capacity. Higher amounts (4-6%) of extract showed the highest antioxidant activity, the lowest oxygen permeability and high stiffness and poor extensibility. The phenolic extracts affected predominantly the mechanical properties, whereas other changes could mainly be correlated to the lower glycerol content which was partially substituted by the extract.

Genetic diversity and antimicrobial activity of lactic acid bacteria in the preparation of traditional fermented potato product 'tunta'.

Fermentation microorganisms, lactic acid bacteria (LAB) and yeast from 12 samples of tunta production chain were quantified, from the native potatoes used by the process fermentation of potatoes in the river up to the final product. During fermentation, the LAB population steadily increased from 3 to 4 to 8 log CFU/g during the first 8 days in the river and the yeast population increased from 2 to 3 to 3-4 log CFU/g. Overall, 115 LAB strains were isolated using a culture-dependent method. Molecular techniques and 16S rRNA gene sequencing enabled the identification of native species. In LAB isolates, members of the Lactobacillaceae (64%), Leuconostocaceae (9%) and Enterococcaceae (2%) families were identified. The most prevalent LAB species in the tunta production chain was Lactobacillus curvatus, followed by Leuconostoc mesenteroides and Lactobacillus sakei, Lactobacillus brevis and Enterococcus mundtii were also present. Only 13 LAB strains showed anti-listerial activity, and one of them, identified as En. mundtii DSM 4838T [MG031213], produced antimicrobial compounds that were determined to be proteins after treatment with proteolytic enzymes. Based on these results, we suggest that traditional fermented product-derived LAB strains from specific environments could be selected and used for technological application to control pathogenic bacteria and naturally protect food from post-harvest deleterious microbiota.

Photodynamic inactivation of Listeria innocua biofilms with food-grade photosensitizers: a curcumin-rich extract of Curcuma longa vs commercial curcumin.

AIMS: The aim of this work is to assess the potential of curcumin in the photosensitization of biofilms of Listeria. METHODS AND RESULTS: Biofilms of Listeria innocua, were irradiated with blue light in the presence of a curcumin-rich extract of Curcuma longa or commercial curcumin. Similar experiments were conducted with planktonic cells, for comparison. A reduction of 4·9 log in the concentration of viable biofilm cells was obtained with 3·7 mg l-1 of commercial curcumin. Planktonic cells were much more susceptible (6·1 log reduction). A tetracationic porphyrin, used as a reference photosensitizer (PS), caused a very modest inactivation of the biofilm (1·1 log) and complete inactivation of the planktonic form (>8 log). CONCLUSIONS: Curcumin is an effective PS for the photodynamic control of Listeria biofilms and the inactivation efficiency attained with this natural compound is higher than with the porphyrin. This result may point to a better performance of type I PSs against bacterial biofilms by circumventing the limitations to singlet-oxygen diffusion imposed by the extracellular matrix. SIGNIFICANCE AND IMPACT OF THE STUDY: Curcumin represents a promising alternative to the control of bacteria and bacterial biofilms in food products particularly in the case of meat products in which turmeric is used as spice.

Chemical Composition, Antioxidant and Antibacterial Activity of Bunium persicum, Eucalyptus globulus, and Rose Water on Multidrug-Resistant Listeria Species.

This research was aimed at investigating the antioxidant and antibacterial activity of Bunium persicum, Eucalyptus globulus, and rose water on multidrug-resistant Listeria species. The antibiotic resistance of Listeria spp obtained from seafood samples were determined by the Kirby-Bauer method. The antioxidant and antibacterial activity of the essential oils and extracts were evaluated using ferric reducing antioxidant power and microdilution methods, respectively. A total 2 samples (1.88%) were positive for Listeria spp. L monocytogenes was found to be resistant to ampicillin, amoxicillin/clavulanic acid, penicillin, vancomycin, and kanamycin. B persicum essential oil showed the greatest antioxidant activity (248.56 ± 1.09 µM Fe2+/g). The E globulus essential oil showed consistently strong antimicrobial activity against L monocytogenes and L grayi, while rose water showed no antimicrobial activity against any of the tested bacterial strains. The results showed that after adding the B persicum and E globulus essential oils to bacteria, the cell components' release increased significantly.

Fungal chitosan and Lycium barbarum extract as anti-Listeria and quality preservatives in minced catfish.

Listeria monocytogenes is a foodborne bacterial pathogen that causes serious health risks. Chitosan (Ch) is a bioactive polymer that could be effectively applied for foodstuffs biopreservation. Lycium barbarum (Goji berry) is ethnopharmaceutical fruit that have diverse health protecting benefits. Chitosan was produced from A. niger and employed with L. barbarum extract (LBE) as blends for Listeria control and quality biopreservation of African catfish mince (Clarias gariepinus). Chitosan could utterly control L. monocytogenes survival in fish mince and its efficacy was strengthened with added LBE at 0.2 and 0.4%. Blending of fish mince with Ch could effectively reduce the progress of chemical spoilage parameters and this protective effect was greatly enhanced with increased addition of LBE. The sensorial assessment of treated minces indicated panelists preferences for the entire attributes of blended samples with Ch and LBE, particularly with storage prolongation. Scanning micrographs elucidated the antibacterial action of Ch against L. monocytogenes. Results recommended the application of fungal Ch/LBE composites as biopreservatives and anti-listerial agents, through their blending with catfish mince, to eliminate bacterial growth, enhance sensory and storage attributes of preserved fish.

Artemisia arborescens Essential Oil Composition, Enantiomeric Distribution, and Antimicrobial Activity from Different Wild Populations from the Mediterranean Area.

Aerial parts of Artemisia arborescens were collected from different sites of the Mediterranean area (southwestern Algeria and southern Italy) and the chemical composition of their essential oil (EO) extracted by hydrodistillation was studied by both gas chromatography (GC) equipped with an enantioselective capillary column and GC/mass spectrometry (GC/MS). The EOs obtained were tested against several Listeria monocytogenes strains. Using GC and GC/MS, 41 compounds were identified, accounting for 96.0 - 98.8% of the total EO. All EOs showed a similar terpene profile, which was rich in chamazulene, ß-thujone, and camphor. However, the concentration of such compounds varied among the EOs. A. arborescens EO inhibited up to 83.3% of the L. monocytogenes strains, but the inhibitory spectrum varied among the EOs, with those from Algeria showing a higher inhibition degree than the Italian EOs. Such effect likely depended on the ketone (ß-thujone + camphor) content of the EO. The differences in the EO composition support the hypothesis that A. arborescens has at least two different chemotypes: a ß-thujone and a chamazulene type. The EO inhibitory spectrum indicates the A. arborescens EO as a valuable option in the control of the food-borne pathogens.

The Antibiofilm Effect of Ginkgo biloba Extract Against Salmonella and Listeria Isolates from Poultry.

Salmonella spp. and Listeria spp. are common foodborne pathogens in poultry and have caused a large number of outbreaks worldwide. Biofilm formation is common in the food industry and is also a mechanism of antimicrobial resistance. The aim of this work was to investigate the antimicrobial effect and mechanism of Ginkgo biloba extract against the biofilm formation of Salmonella and Listeria isolates from poultry at retail markets. Bacteria detection, isolation, and enumeration were carried out on 27 chicken and 29 ducks at retail markets. The effects of temperature and G. biloba extract against biofilm formation of Salmonella and Listeria isolates were measured using the crystal violet assay and swimming and swarming motilities. The monitoring results of Salmonella and Listeria in 56 poultry carcasses at retail markets in Korea showed that the prevalence of Salmonella spp. in poultry was low (5.4%), but the prevalence of Listeria spp (78.6%) was high. L. innocua was the predominant serotype (80%) in the isolated Listeria species. Temperature, strain, and surface affected the biofilm formation of Salmonella spp. and Listeria spp. L. innocua showed the best biofilm formation ability on a 96-well plate, while Salmonella Enteritidis formed the most biofilm on a glass slide. Biofilm formation abilities of Salmonella spp. and Listeria spp. were increased with the increase of temperature. G. biloba extract at 75 µg/mL significantly inhibited biofilm formation of Salmonella spp. and Listeria spp (p < 0.05). The mechanism of the antibiofilm effect of the G. biloba extract showed that the motility reduction may be one of the mechanisms of G. biloba extract against some serotypes of Salmonella and Listeria, but not L. monocytogenes. The findings of this study provided the basis for the application of G. biloba extract as a food additive to promote the quality and safety of poultry products.

Antimicrobial Activity of Rhoeo discolor Phenolic Rich Extracts Determined by Flow Cytometry.

Traditional medicine has led to the discovery of important active substances used in several health-related areas. Phytochemicals in Rhoeo discolor extracts have proven to have important antimicrobial activity. In the present study, our group determined the antimicrobial effects of extracts of Rhoeo discolor, a plant commonly used in Mexico for both medicinal and ornamental purposes. We evaluated the in vitro activity of phenolic rich extracts against specifically chosen microorganisms of human health importance by measuring their susceptibility via agar-disc diffusion assay and flow cytometry: Gram-positive Listeria innocua and Streptococcus mutans, Gram-negative Escherichia coli and Pseudomonas aeruginosa, and lastly a fungal pathogen Candida albicans. Ten different extracts were tested in eight different doses on all the microorganisms. Analytical data revealed a high content of phenolic compounds. Both agar-disc diffusion assay and flow cytometry results demonstrated that Pseudomonas aeruginosa was the least affected by extract exposure. However, low doses of these extracts (predominantly polar), in a range from 1 to 4 µg/mL, did produce a statistically significant bacteriostatic and bactericidal effect on the rest of the microorganisms. These results suggest the addition of certain natural extracts from Rhoeo discolor could act as antibacterial and antimycotic drugs or additives for foods and cosmetics.

Phytochemical Characterization of Veronica officinalis L., V. teucrium L. and V. orchidea Crantz from Romania and Their Antioxidant and Antimicrobial Properties.

Aerial parts of Veronica species are used in Romanian traditional medicine for the treatment of various conditions like kidney diseases, cough, and catarrh, and are known for their wound-healing properties. In the present study, the phenolic and sterolic content and the antioxidant and antimicrobial activities of three Veronica species (Plantaginaceae), V. officinalis L., V. teucrium L. and V. orchidea Crantz, were studied. The identification and quantification of several phenolic compounds and phytosterols were performed using LC/MS techniques and the main components were p-coumaric acid, ferulic acid, luteoline, hispidulin and ß-sitosterol. More than that, hispidulin, eupatorin and eupatilin were detected for the first time in the Veronica genus. Nevertheless, representatives of the Veronica genus were never investigated in terms of their phytosterol content. The antioxidant potential investigated by Trolox equivelents antioxidant capacity (TEAC) and EPR spectroscopy revealed that V. officinalis and V. orchidea extracts presented similar antioxidant capacities, whilst the values registered for V. teucrium extract are lower. Regarding the antimicrobial activity of the investigated species, Staphylococcus aureus, Listeria monocytogenes and Listeria ivanovii were the most sensitive strains with MIC values between 3.9 and 15.62 mg/mL. The results obtained by this study may serve to promote better use of representatives from the genus Veronica as antioxidant and antimicrobial agents.

Effect of emulsification and spray-drying microencapsulation on the antilisterial activity of transcinnamaldehyde.

Spray-dried redispersible transcinnamaldehyde (TC)-in-water emulsions were prepared in order to preserve its antibacterial activity; 5% (w/w) TC emulsions were first obtained with a rotor-stator homogeniser in the presence of either soybean lecithin or sodium caseinate as emulsifiers. These emulsions were mixed with a 30% (w/w) maltodextrin solution before feeding a spray-dryer. The antibacterial activity of TC alone, TC emulsions with and without maltodextrin before and after spray-drying were assayed by monitoring the growth at 30 °C of Listeria innocua in their presence and in their absence (control). Whatever the emulsifier used, antilisterial activity of TC was increased following its emulsification. However, reconstituted spray-dried emulsions stabilised by sodium caseinate had a higher antibacterial activity suggesting that they better resisted to spray-drying. This was consistent with observation that microencapsulation efficiencies were 27.6% and 78.7% for emulsions stabilised by lecithin and sodium caseinate, respectively.

Effect of a Vietnamese Cinnamomum cassia essential oil and its major component trans-cinnamaldehyde on the cell viability, membrane integrity, membrane fluidity, and proton motive force of Listeria innocua.

The antibacterial mechanism of a Cinnamomum cassia essential oil from Vietnam and of its main component (trans-cinnamaldehyde, 90% (m/m) of C. cassia essential oil) against a Listeria innocua strain was investigated to estimate their potential for food preservation. In the presence of C. cassia essential oil or trans-cinnamaldehyde at their minimal bactericidal concentration (2700 µg·mL(-1)), L. innocua cells fluoresced green after staining with Syto9® and propidium iodide, as observed by epifluorescence microscopy, suggesting that the perturbation of membrane did not cause large pore formation and cell lysis but may have introduced the presence of viable but nonculturable bacteria. Moreover, the fluidity, potential, and intracellular pH of the cytoplasmic membrane were perturbed in the presence of the essential oil or trans-cinnamaldehyde. However, these membrane perturbations were less severe in the presence of trans-cinnamaldehyde than in the presence of multicomponent C. cassia essential oil. This indicates that in addition to trans-cinnamaldehyde, other minor C. cassia essential oil components play a major role in its antibacterial activity against L. innocua cells.

Chemical composition and antibacterial activities of seven Eucalyptus species essential oils leaves.

BACKGROUND: In this paper, we have studied the essential oils chemical composition of the leaves of seven Eucalyptus species developed in Tunisia. Eucalyptus leaves were picked from trees growing in different arboretums in Tunisia. Choucha and Mrifeg arboretums located in Sedjnene, region of Bizerte (Choucha: E. maideni, E. astrengens et E. cinerea; Mrifeg : E. leucoxylon), Korbous arboretums located in the region of Nabeul, North East Tunisia with sub-humid bioclimate, (E. lehmani), Souiniet-Ain Drahem arboretum located in region of Jendouba (E. sideroxylon, E. bicostata). Essential oils were individually tested against a large panel of microorganisms including Staphylococcus aureus (ATCC 6539), Escherichia coli (ATCC 25922), Enterococcus faecalis (ATCC29212), Listeria ivanovii (RBL 30), Bacillus cereus (ATCC11778). RESULTS: The yield of essential oils ranged from 1.2% to 3% (w/w) for the different Eucalyptus species. All essential oils contain α-pinene, 1,8-cineol and pinocarveol-trans for all Eucalyptus species studied. The 1,8-cineol was the major compound in all species (49.07 to 83.59%). Diameter of inhibition zone of essential oils of Eucalyptus species varied from 10 to 29 mm. The largest zone of inhibition was obtained for Bacillus cereus (E. astrengens) and the lowest for Staphylococcus aureus (E. cinerea). The essential oils from E. maideni, E. astrengens, E. cinerea (arboretum of Bizerte), E. bicostata (arboretum of Aindraham) showed the highest antibacterial activity against Listeria ivanovii and Bacillus cereus. CONCLUSION: The major constituents of Eucalyptus leaves essential oils are 1,8-cineol (49.07 to 83.59%) and α-pinene (1.27 to 26.35%). The essential oils from E. maideni, E. astrengens, E. cinerea, E. bicostata showed the highest antibacterial activity against Listeria ivanovii and Bacillus cereus, they may have potential applications in food and pharmaceutical products.

Chemical composition and antibacterial activities of seven Eucalyptus species essential oils leaves

BACKGROUND: In this paper, we have studied the essential oils chemical composition of the leaves of seven Eucalyptus species developed in Tunisia. Eucalyptus leaves were picked from trees growing in different arboretums in Tunisia. Choucha and Mrifeg arboretums located in Sedjnene, region of Bizerte (Choucha: E. maideni, E. astrengens et E. cinerea; Mrifeg : E. leucoxylon), Korbous arboretums located in the region of Nabeul, North East Tunisia with sub-humid bioclimate, (E. lehmani), Souiniet-Ain Drahem arboretum located in region of Jendouba (E. sideroxylon, E. bicostata). Essential oils were individually tested against a large panel of microorganisms includingStaphylococcus aureus (ATCC 6539), Escherichia coli (ATCC 25922), Enterococcus faecalis (ATCC29212), Listeria ivanovii (RBL 30), Bacillus cereus (ATCC11778). RESULTS: The yield of essential oils ranged from 1.2% to 3% (w/w) for the different Eucalyptus species. All essential oils contain α-pinene, 1,8-cineol and pinocarveol-trans for all Eucalyptus species studied. The 1,8-cineol was the major compound in all species (49.07 to 83.59%). Diameter of inhibition zone of essential oils of Eucalyptus species varied from 10 to 29 mm. The largest zone of inhibition was obtained for Bacillus cereus (E. astrengens) and the lowest for Staphylococcus aureus (E. cinerea). The essential oils from E. maideni, E. astrengens, E. cinerea (arboretum of Bizerte), E. bicostata(arboretum of Aindraham) showed the highest antibacterial activity against Listeria ivanovii and Bacillus cereus. CONCLUSION: The major constituents of Eucalyptus leaves essential oils are 1,8-cineol (49.07 to 83.59%) and α-pinene (1.27 to 26.35%). The essential oils from E. maideni, E. astrengens, E. cinerea, E. bicostatashowed the highest antibacterial activity against Listeria ivanovii and Bacillus cereus, they may have potential applications in food and pharmaceutical products.

The antimicrobial activity of Liquidambar orientalis mill. against food pathogens and antioxidant capacity of leaf extracts.

BACKGROUND: Medicinal plants are an important source of substances which are claimed to induce antimicrobial, antimutagenic and antioxidant effects. Many plants have been used due to their antimicrobial treatments. Antimicrobial and antioxidant activities of L. orientalis have not been reported to the present day. The aim of this work was to investigate of the antimicrobial and antioxidant potentials of different extracts from L. orientalis. MATERIALS AND METHODS: The extracts were screened for antimicrobial activity against different food pathogens. These bacteria include 4 Gram positive and 3 Gram negative bacteria and one fungi. The leaf extracts of plant were tested by disc diffusion assay. The MIC was evaluated on plant extracts as antimicrobial activity. In addition to, the plant extracts were tested against the stable DPPH (2,2-diphenyl-1-picryl-hydrazylhydrate) free-radical. RESULTS: The acetone, ethanol and methanol extracts of L. orientalis showed maximum inhibition zone of 12 mm against Yersinia enterocolitica, Listeria monocytogenes and Staphylococcus aureus. In addition to, the methanol extract displayed a strong antioxidant activity (trolox equivalent = 2.23 mM). CONCLUSION: L. orientalis extracts have antimicrobial, and antioxidant potential. Our results support the use of this plant in traditional medicine and suggest that some of the plant extracts possess compounds with good antibacterial properties that can be used as antibacterial agents in the search for new drugs.