In vitro enhancement of antibiotic susceptibility of drug resistant Escherichia coli by cinnamaldehyde

Cinnamaldehyde is a natural antimicrobial compound that has been found to damage the cytoplasmic membrane, inhibit septum development and cause cell elongation, as well as induce oxidative stress in Escherichia coli. Thus, cinnamaldehyde may be of value as a natural compound to enhance susceptibility of drug resistant E. coli to antibiotics in livestock production. This study examined the ability of cinnamaldehyde to increase the susceptibility of E. coli to antibiotics using the checkerboard method. Interactions between the antimicrobials were characterized using fractional inhibitory concentration (FIC) values. All tested E. coli strains were resistant to erythromycin and bacitracin but were susceptible to penicillin G and ampicillin. Strains 8WT, ATCC 23739 and 02:0627 were resistant to novobiocin and the latter two strains were also resistant to tetracycline. Cinnamaldehyde synergistically increased the susceptibility of all E. coli strains to erythromycin (FIC ≤ 0.5). Another synergistic effect between tetracycline and cinnamaldehyde was observed when tested against E. coli ATCC 23739 (FIC = 0.3). Cinnamaldehyde synergistically and additively reduced the MIC of novobiocin when tested against ATCC 23739 and 02:0627 (FIC ≤ 0.5) or 8WT (FIC = 1), respectively, suggesting that E. coli strains may respond differently to challenge by the cinnamaldehyde-novobiocin combination. With all strains, cinnamaldehyde was not effective at reducing the MIC value of bacitracin. Findings of this study suggest that cinnamaldehyde may be used in combination with several antibiotics to enhance susceptibility of drug resistant E. coli.     

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.     

Antimicrobial resistance of Escherichia coli and Staphylococcus aureus isolated from food handler's hands

The aim of this study was to determine the antimicrobial resistance of Escherichia coli and Staphylococcus aureus isolates from food handlers' hands at primary schools in Hulu Langat district, Selangor (Malaysia). Disc diffusion methods were used to examine the antimicrobial resistance of the bacteria by using ten types of antibiotic discs with different concentrations. The results show that the prevalence of S. aureus (65.88–74.12%) was far higher than the prevalence of E. coli (9.41–14.12%). The percentage isolates of E. coli that were resistant to the antibiotics was 85.71% Penicillin and Chloramphenicol, 57.14% Sulfamethoxazole-Trimethoprim, Ampicillin and Trimethoprim, 28.57% Kanamycin and Tetracycline and 14.29% Ciprofloxacin. All of the isolates had shown susceptible to Gentamicin and Nitrofurantoin. For S. aureus, the percentage isolates that were resistant to the antibiotics was 72.30% Ampicillin, 53.38% Penicillin, 4.73% Nitrofurantoin,1.35% Chloramphenicol and Trimethoprim and 0.68% Kanamycin and Tetracycline. None of the isolates had shown resistant to Ciprofloxacin, Sulfamethoxazole-Trimethoprim and Gentamicin. Multidrug resistant Escherichia coli represented a high percentage (85.71%) of the total positive strains revived whereas multidrug resistant S. aureus strains were only 5.41% of the total positive strains. The existence of multidrug resistant bacteria is quite worrying as they may pose serious threat to the patients. Hence, the microbiological quality of food handlers' hands from foodservice operations should be maintained in a good condition to reduce the existence of multidrug resistance bacteria.     

Antibiofilm activity of essential oils and plant extracts against Staphylococcus aureus and Escherichia coli biofilms

Bacterial biofilms pose health risks in clinical environments, food industry and drinking water systems. Here, we investigated in vitro antibiofilm activities of essential oils (EO) and plant extracts of peppermint (Mentha × piperita L.), coriander (Coriandrum sativum L.), and anise (Pimpinella anisum L.). Minimum inhibitory concentration assay (MIC) was carried out using two-fold serial dilution method and MTT assay against Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. Biofilm growth and development were assessed using crystal violet (CV) and XTT reduction assays. Antibacterial activity was observed for almost all plant extracts and all EOs against both bacterial strains with stronger activity against S. aureus. All EOs (at MIC value of 0.8 to 0.63 μl/ml) and 8 out of 14 plant extracts (at MIC value of 2–4 mg/ml) inhibited bacteria cell attachment of both bacteria. CV and XTT reduction assay for the plant extracts and EOs with inhibition of bacteria attachment by at least 50%, demonstrated that coriander EO had the highest antibiofilm activity against biofilm formed by both tested bacteria (S. aureus and E. coli) at lowest MIC value 0.8 μl/ml and 1.6 μl/ml, respectively, indicating further investigations due to the oil's high antibiofilm activity potential.     

Growth inhibition and morphological alterations of Fusarium verticillioides by cinnamon oil and cinnamaldehyde

Fusarium verticillioides is a filamentous fungus and a widely distributed pathogen having the ability to infect and cause destruction in economically important crops and grains by producing fumonisin mycotoxins. In the present study, the inhibitory effect of cinnamon, citral, Litsea cubeba oil, clove, eucalyptus, anise, spearmint and camphor oils on F. verticillioides was investigated, and cinnamon oil proves to be the most effective in inhibition. The antifungal effect of cinnamon oil was studied with special reference to its mechanism of inhibition of F. verticillioides growth at the morphological and ultrastructural levels. For F. verticillioides, the minimal inhibitory concentrations (MICs) of cinnamon oil (85% cinnamaldehyde), natural cinnamaldehyde (95%), and synthetic cinnamaldehyde (99%) were 60, 50, and 45 μL/L, respectively. The antifungal activity of cinnamon oil was proportional to its cinnamaldehyde concentration. Scanning electron microscopy and transmission electron microscopy of F. verticillioides exposed to MIC of cinnamaldehyde showed irreversible deleterious morphological and ultrastructural alterations, such as lack of cytoplasmic contents, loss of integrity and rigidity of the cell wall, plasma membrane disruption, mitochondrial destruction, folding of the cell. These modifications induced by cinnamaldehyde may be due to its interference with enzymatic reactions of cell wall synthesis, thus affecting the morphogenesis and growth of the fungus. These results further emphasized the toxicity of cinnamon oil against F. verticillioides attacking grains, and that cinnamon oil could be safely used as an alternative to chemical fungicides during grain storage and in the field.     

Removing Staphylococcus aureus and Escherichia coli biofilms on stainless steel by cleaning-in-place (CIP) cleaning agents

We investigated the effects of cleaning-in-place (CIP) cleaning agents, food additives and other compounds (EDTA, Tween20 and SDS) on the removal of Staphylococcus aureus and Escherichia coli biofilm from stainless steel plates. S. aureus formed thick biofilm and was more resistant to cleaning than E. coli biofilm. Strong acidic and strong alkaline CIP cleaning agents showed a significant cleaning effect. Strong alkaline CIP cleaning agents were especially effective for the removal of S. aureus biofilm.     

Rutin inhibits mono and multi-species biofilm formation by foodborne drug resistant Escherichia coli and Staphylococcus aureus

Considering the role of biofilm in food spoilage and the food industry, inhibition of biofilm formation by natural agents is expected to be safe and could also enhance the efficacy of other antimicrobial strategies for controlling microbial food spoilage. Plant flavonoids are known for their diverse biological activity including antimicrobial. Therefore, rutin was investigated for its biofilm inhibitory activity at sub-minimum inhibitory concentrations (sub-MICs) values against common foodborne pathogens (Escherichia coli and Staphylococcus aureus). Minimum inhibitory concentrations (MIC) ranged from 400 to 1600 μg/ml against the selected strains. Sub-MICs (1/16 × MIC to 1/2 × MIC) were used to assess the inhibition of biofilm formed by E. coli and S. aureus in microtitre plate assay. Mono strain biofilm formation by Escherichia coli and Staphylococcus aureus was greatly reduced by rutin at their respective 1/2 × MIC. For multi-species (E. coli: and S. aureus) biofilm formation, the reduction in biofilm production was concentration dependent. No significant bacteria mass reduction was recorded for any sub-MIC. SEM images of biofilm inhibition on steel chips confirmed the reduction in number of microcolonies. Exopolysaccharide production responsible for adherence and maturation of biofilms was also significantly (p ≤ 0.05) reduced at respective concentrations of rutin in tested strains. To the best of our knowledge, this is the first study describing the effect of flavonoid, rutin on multi-species biofilms consisting of S. aureus and E. coli. Findings of the study indicate a potential application of rutin in the prevention of biofilm on industrial equipment and food contact surfaces and prevent food contamination and spoilage.     

Bactericidal action of slightly acidic electrolyzed water against Escherichia coli and Staphylococcus aureus via multiple cell targets

This study combined plate counting method and fluorescent techniques (membrane integrity and potential, intracellular enzyme activity, and intracellular ROS level) to investigate the lethal and sublethal effects of slightly acidic electrolyzed water (SAEW) on Escherichia coli and Staphylococcus aureus. Also, the inactivation mechanism of SAEW was further explored through multiple cell targets (outer membrane and intracellular components). The results within 30 s SAEW treatment displayed 6.02 and 5.83 log reductions obtained for E. coli and S. aureus, respectively. The maximum sublethally injured cell proportions induced by SAEW exposure were 0.34 and 0.40 log₁₀ CFU/mL for E. coli and S. aureus, respectively. According to the data from experiments of various acting cellular sites by fluorescent techniques, SAEW damaged the microbial membrane integrity and membrane potential severely. Also, it posed inactivation effect on the activity of intracellular esterase enzymes. Therefore, SAEW showed disinfection behavior with multiple cellular targets, including both cell barriers and intracellular components. Furthermore, SAEW did not result in accumulation of reactive oxygen species (ROS) inside microbial cell, indicating SAEW conducted a ROS-independent behavior on microbial inactivation and the chemical oxidants (e.g., hypochlorous acid) played major role in microbial intracellular oxidation processing. The result in this study will help to further understand the disinfection mechanism underlying SAEW on microorganisms and make SAEW inactivation targets more explicit.     

Growth of Escherichia coli and Staphylococcus aureus in individual lasagne layers and evidence for migration of E. coli throughout the product

Growth of Escherichia coli and Staphylococcus aureus within individual layers of lasagne was studied after spiking of ～10⁵–10⁶ CFU/g of each bacterial species into bolognese or béchamel sauces. Both E. coli and S. aureus grew by 3–4 log₁₀ cycles in each meal component. In a second study, alternate layers within a composite lasagne meal were spiked with ～10⁵–10⁶ CFU/g of E. coli and adjoining layers were monitored for possible bacterial migration. Spiked composite meals were subjected to either low temperature storage at 4 °C up to 8 h or to freeze chilling, which involved freezing at ?18 °C for 24 h followed by thawing at 4 °C up to 40 h. Migration of E. coli from inoculated layers to the adjoining layers was indicated by a recovery of substantial populations following both storage treatments. Migration appeared to be more limited for meals which underwent freeze chill treatment. In contrast, migration was evident throughout all product layers in meals stored at 4 °C only. Migration of bacteria throughout a multi-layered food may arise from differing compositional or structural characteristics within the product or from differing storage treatments. Therefore as a result of bacterial migration, it would appear that microbiological safety of multi-layered products such as lasagne relies on ensuring safety of each individual layer.     

Investigation into the antibacterial behavior of suspensions of magnesium oxide nanoparticles in combination with nisin and heat against Escherichia coli and Staphylococcus aureus in milk

The antibacterial activities of magnesium oxide nanoparticles (MgO NP) alone or in combination with nisin against Escherichia coli and Staphylococcus aureus were investigated. Synergistic antibacterial effects existed and at lower levels of nisin when compared to when nisin was used alone. Also the antibacterial activities of MgO NP in combination with other antimicrobials (nisin and heat) against E. coli and S. aureus were investigated in milk. A synergistic effect of MgO NP in combination with nisin and heat was observed as well. Scanning electron microscopy was used to characterize the morphological changes of E. coli after antimicrobial treatments. It was revealed that MgO NP treatments in combination with nisin distort and damage the cell membrane, resulting in a leakage of intracellular contents and eventually the death of bacterial cells. This is the first report describing the antibacterial activity of MgO NPs and nisin in milk. It leads the way to development of treatment combinations which could result in a decrease in pasteurisation temperatures and the level of MgO NP required for pasteurising milk and maintaining pathogen control.     

Biofilm formation by Salmonella Typhimurium and Staphylococcus aureus on stainless steel under either mono- or dual-species multi-strain conditions and resistance of sessile communities to sub-lethal chemical disinfection

Intercellular interactions encountered within and between different bacterial species are believed to play key roles in both biofilm formation and antimicrobial resistance. In this study, Salmonella Typhimurium and Staphylococcus aureus (3 strains per species) were left to form biofilms on stainless steel coupons incubated at 20 °C for 144 h (i.e. 6 days), in periodically renewable growth medium, under either mono- or dual-species conditions. Subsequently, the developed sessile communities were exposed for 6 min to sub-lethal concentrations of: (i) benzalkonium chloride (BC, 50 ppm), (ii) sodium hypochlorite (NaClO, 10 ppm), or (iii) peroxyacetic acid (PAA, 10 ppm). The dominance of each strain in the mono- and dual-species biofilm communities, both before and after disinfection, was monitored by pulsed field gel electrophoresis (PFGE). Results revealed that dual-species conditions led to a significant (ca. 10-fold) reduction in the number of sessile cells for both species, compared to mono-species ones, with interspecies interactions however found to not exert any significant effect on the disinfection resistance of each species as a whole. However, PFGE analysis revealed that the different strains here employed behaved differently with regard to biofilm formation and disinfection resistance, with this effect to be also strongly dependent on the culture conditions (mono-/dual-species) and the disinfectant applied. Such results expand our knowledge on multi-species biofilms formed by foodborne pathogenic bacteria and could hopefully be helpful in our efforts to develop effective elimination strategies and thus improve food safety.     

Sanitization potency of slightly acidic electrolyzed water against pure cultures of Escherichia coli and Staphylococcus aureus,in comparison with that of other food sanitizers

The sanitization potency of slightly acidic electrolyzed water (SAEW) on pure cultures of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) was evaluated. The potency was compared with that of strong acidic electrolyzed water (StAEW) and sodium hypochlorite (NaOCl) solution. SAEW (ca. pH 5.8 and 21 mg/l available chlorine concentration; ACC) resulted into >5 log₁₀CFU/ml reduction of E. coli and S. aureus after 90 s of exposure. The relative bacterial reduction potency at each exposure time was in the order StAEW > NaOCl > SAEW and increased with exposure time, with relative effect being 90 s > 60 s > 30 s. The results indicate that SAEW with low ACC and near neutral pH can potentially sanitize E. coli and S. aureus within a short period of exposure presenting a potential replacement to NaOCl solution commonly used in the food industry.     

ZnO nanoparticle suspensions containing citric acid as antimicrobial to control Listeria monocytogenes,Escherichia coli,Staphylococcus aureus and Bacillus cereus in mango juice

Zinc oxide (ZnO) nanoparticles have been proven to have strong antibacterial activity against food borne pathogens. The practical applications of different concentrations (0, 1, 3, 5 and 8 mM) of ZnO suspensions containing 0.3% citric acid were investigated against the pathogenic bacteria like, Listeria monocytogenes, Escherichia coli, Staphylococcus aureus and Bacillus cereus. Zinc oxide suspensions (0, 1, 3, 5 and 8 mM) containing citric acid have shown a significant inhibitory effect on the growth of all strains during 12 h of incubation. Our results have also shown that 5 and 8 mM suspensions of ZnO were the most effective on all strains. These data suggested that the antibacterial activity of ZnO was concentration dependent. Thus 5 mM and 8 mM ZnO were selected for further studies, carried out in mango juice, as they showed a significant growth inhibition in TSB. ZnO NPs were more capable of reducing initial growth counts of all the above stated strains in mango juice. Results have also exhibited that ZnO and citric acid had inhibitory effect on the growth of all strains during 24 h culture period in mango juice, as compared to the control experiment, which was further confirmed in liquid culture. This is the first report, describing the antibacterial activity of ZnO NPs in mango juices that showed the potential of these nanoparticles for use as an antibacterial agent in the food industry.     

The efficacy of chemical sanitizers on the reduction of Salmonella Typhimurium and Escherichia coli affected by bacterial cell history and water quality

Washing fresh produce with potable water helps to remove microorganisms, providing about a 1- to 2-log reduction, but this process can also pose an opportunity for cross-contamination of bacteria in the washing tank. The objective of this study was to evaluate the efficacy of three chemical sanitizers, sodium hypochlorite, chlorine dioxide, and a silver-copper solution on the reduction of S. Typhimurium and extended-spectrum beta-lactamase (ESBL) E. coli as well as to evaluate the impact bacterial cell history and water quality had on sanitizer efficacy. This was investigated with three scenarios representing different contamination routes and history of cells: (i) on starved and non-starved cells in potable water, (ii) on starved and non-starved cells in lettuce wash water and on lettuce leaf punches, and (iii) on non-starved cells in organically loaded process wash water (PWW). Sodium hypochlorite (NaClO) and chlorine dioxide (ClO₂) were more effective in preventing cross-contamination in the potable water than the silver-copper solution. Starved and non-starved bacterial cells displayed minor differences in their susceptibility to sanitizing agents in the (i) potable water and (ii) lettuce wash water demonstrating that other conditions greater influenced sanitizer efficacy. Particularly, the organic load of the water, wash water temperature, and pathogen attachment and release from the produce were shown to affect a sanitizer's efficacy during washing. Furthermore, results emphasize that chemical sanitizer use should focus more on wash water disinfection, rather than produce decontamination, to prevent pathogenic cross-contamination during processing. Future research should investigate the feasibility of ClO₂ application during pilot-scale processing.     

High-pressure processing and boiling water treatments for reducing Listeria monocytogenes,Escherichia coli O157:H7, Salmonella spp., and Staphylococcus aureus during beef jerky processing

Beef jerky is a convenient, ready-to-eat meat product, but requires processing lethality steps to ensure the safety of the product. Previous outbreaks involving various jerky products have highlighted the risks associated with jerky and the importance of utilizing pathogen interventions during processing. In this study, two alternative interventions were evaluated for reducing pathogen populations during jerky processing. Results demonstrated that high pressure processing (HPP; two treatments of 550 MPa, 60 s) could produce significant (p < 0.05), but variable reductions (6.83 and 4.45 log₁₀ CFU/strip) of Salmonella spp. and Escherichia coli O157:H7, respectively, on resulting beef jerky. HPP treatments, however, produced minor reductions (p < 0.05) of Gram-positive pathogens, resulting in reductions of 1.28 and 1.32 log₁₀ CFU/strip of Listeria monocytogenes and Staphylococcus aureus, respectively. Alternatively, boiling water (100 ± 2 °C) treatments (20–30 s) used after marination and prior to dehydration, reduced Salmonella spp., E. coli O157:H7, L. monocytogenes, and S. aureus populations >5.0 log₁₀ CFU/strip in resulting beef jerky. Thus, 20 or 30 s boiling water (100 ± 2 °C) treatments could be effective interventions for commercial jerky processors or home food preservers. Future validation of these processes in-plant could provide processors and regulators with alternative strategies for safe and shelf-stable jerky products.     

Suitability of ccRSM as a tool to predict inactivation and its kinetics for Escherichia coli,Staphylococcus aureus and Pseudomonas fluorescens in homogenized milk treated by manothermosonication (MTS)

The application of ultrasound (US) technology (i.e. sonication) has been used as an alternative to thermal technologies to reduce the microbial population of foods and beverages. This approach can be used on its own or combined with pressure and temperature (i.e. manothermosonication (MTS)). Microbial inactivation kinetics by sonication remains unclear. In the present study, a central composite response surface model (ccRSM) was used in order to study the effects of temperature (20–52 °C), acoustic intensity (60–120 W/cm²) and treatment time (40–240 s) at a constant pressure (225 kPa) by MTS processing on microbial inactivation. Reductions of up to c. 1.6 log CFU/ml were achieved for Escherichia coli and Pseudomonas fluorescens. Lower inactivation values were reported for Staphylococcus aureus (1.05 log CFU/ml). These inactivation values were achieved using conditions of 36 °C, 90 W/cm² and 240 s. Inactivation of E. coli by MTS (R² = 0.90) was described by an exponential curve, whereas inactivation of S. aureus and P. fluorescens by MTS (R² ≥ 0.73) were described by a linear trend. The coefficient of determination values were obtained following validation between the theoretical model and the experimental values. Statistical analysis showed that treatment time was the factor with greatest influence on microbial inactivation for all three microorganisms. The present study confirms the suitability of using ccRSM as a tool for investigating and predicting the inactivation of E. coli, S. aureus and P. fluorescens as a function of temperature, acoustic power and treatment time, and may also be useful for predicting inactivation of other microorganisms commonly found in raw milk.     

The effect of pulsed UV light on Escherichia coli O157:H7, Listeria monocytogenes,Salmonella Typhimurium,Staphylococcus aureus and staphylococcal enterotoxin A on sliced fermented salami and its chemical quality

Pulsed UV light (PL) applied at a fluence of 3 J/cm² was effective to reduce Listeria monocytogenes, Escherichia coli 0157:H7, Salmonella Typhimurium and Staphylococcus aureus for 2.24, 2.29, 2.25 and 2.12 log CFU/g on the surface of dry fermented salami. Further increase in the fluence of PL treatment did not increase levels of microbial inactivation. However, the time interval between the contamination and PL treatment was found to have a significant impact on the efficacy of PL treatment and should be kept as short as possible. After initial PL treatment slices of fermented salami were packed in vacuum or in 80%CO₂/20%N₂ modified atmosphere and stored at 4 °C to investigate the effect of PL treatment on protein and lipid oxidation as the shelf life of fermented salami is not usually limited by microbial deterioration, but by chemical and sensory alterations. In this study observed lipid oxidation values for PL treated vacuum and modified atmosphere packed fermented salami slices fall within the acceptable threshold for the rancid odor, except for the sample treated with the highest fluence tested (15 J/cm²), packed in modified atmosphere and kept in cold storage for 9 weeks (1.23 mg MDA/kg). All values were below the threshold for rancid flavor, too. The significant rise in protein oxidation of PL treated fermented salami slices, perceived as 28% increase of carbonyl content compared to untreated samples, was observed only after 9 weeks of cold storage in both vacuum and modified atmosphere packed samples. The results of chemical analysis are in agreement with previously published results of sensory analysis. Current results show the applicability of PL to improve microbial safety of sliced fermented salami that are prone to cross-contamination without affecting quality attributes by lipid and protein oxidation.     

Membrane disruption and DNA binding of Staphylococcus aureus cell induced by a novel antimicrobial peptide produced by Lactobacillus paracasei subsp. tolerans FX-6

Previously, we have isolated a novel bacteriocin, peptide F1 from Tibetan Kefir, and demonstrated its superior antimicrobial activity. However, its antimicrobial mechanism is still undefined. This study was aimed to elucidate the antimicrobial mechanism of peptide F1 against Staphylococcus aureus. The antimicrobial effects of peptide F1 were characterized by the following methods: chemical assay to quantify cytoplasmic β-galactosidase leakage, atomic absorption spectrometry to measure the released potassium ions, transmission electron microscopy to visualize the cellular morphological changes, and electrophoresis analysis and atomic force microscopy together to exam the DNA binding activity. Our results revealed that peptide F1 exerted its bactericidal effects by damaging bacterial cell membranes and by binding to the genomic DNA in the cytoplasm, which both led to rapid cell death.     

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.