Effect of hydrogen peroxide vapor treatment for inactivating Salmonella Typhimurium,Escherichia coli O157:H7 and Listeria monocytogenes on organic fresh lettuce

In this study, the efficacy of hydrogen peroxide vapor (HPV) for reducing Salmonella Typhimurium, Escherichia coli O157:H7 and Listeria monocytogenes on lettuce was investigated as well as its effect on lettuce quality. Lettuce was inoculated with a cocktail containing three strains of each pathogen then treated with vaporized hydrogen peroxide for 0, 2, 4, 6, 8 and 10 min. The concentrations of hydrogen peroxide used were 0, 1, 3, 5 and 10%. With increasing treatment time and hydrogen peroxide concentration, HPV treatment showed significant (P < 0.05) reduction compared to the control (0%, treated with vaporized distilled water). In particular, vaporized 10% hydrogen peroxide treatment for 10 min was the most effective combination for reducing the three pathogens on lettuce. The reduction levels of S. Typhimurium, E. coli O157:H7 and L. monocytogenes on lettuce were 3.12, 3.15 and 2.95 log₁₀ CFU/g, respectively. Furthermore, there were no significant (P > 0.05) quality changes (color and texture) of lettuce among all tested samples, and hydrogen peroxide residues were not detected after 36 h storage time in any of the treated samples. These results suggest that HPV treatment could be an alternative method for reducing S. Typhimurium, E. coli O157:H7 and L. monocytogenes on fresh produce.     

Effect of combination of ultraviolet light and hydrogen peroxide on inactivation of Escherichia coli O157:H7, native microbial loads,and quality of button mushrooms

Mushrooms are prone to microbial spoilage and browning during growing and processing. Ultraviolet light (254 nm, UV-C) has been used as an alternative technology to chemical sanitizersfor food products. Hydrogen peroxide (H₂O₂) is classified as generally recognized as safe for use in foods as a bleaching and antimicrobial agent, and could control the bacterial blotch and browning of mushrooms. This study investigated the effects of water wash (control), 3% H₂O₂ wash, 0.45 kJ m⁻² UV-C, and combination of H₂O₂ and UV-C (H₂O₂ + UV) on microbial loads and product quality of mushrooms during storage for 14 days at 4 °C. Additionally, the inactivation of Escherichia coli O157:H7 inoculated on mushrooms was determined. Results showed that water wash, H₂O₂, UV-C and H₂O₂ + UV resulted in 0.44, 0.77, 0.85, and 0.87 logs CFU g⁻¹ reduction of E. coli O157:H7, respectively. Hydrogen peroxide, UV-C and the combination reduced total aerobic plate counts on the surface of mushrooms by 0.2–1.4 logs CFU g⁻¹ compared to the control, while there was no significant difference among the three treatments during storage. After storage, UV-C treated mushrooms had similar L* and a* values as the control while H₂O₂ and H₂O₂ + UV-C treated mushrooms had higher L* (lighter) and lower a* (less brown) values than the control. Compared to water wash, all the treatments inhibited lesion development on the mushroom surface on day 14. The combination of H₂O₂ and UV achieved the best overall dual control of lesion and browning. There was no significant difference in ascorbic acid and total phenolic content among the treatments. Overall our results suggested that H₂O₂ + UV reduced microbial loads, and extended storage life by reducing lesion development without causing deterioration in nutritional quality of button mushrooms. Therefore, when properly utilized, H₂O₂ + UV could potentially be used for maintaining postharvest quality while marginally reducing populations of E. coli O157:H7 and background microflora.     

Comparison of effects of mild heat combined with lactic acid on Shiga toxin producing Escherichia coli O157:H7, O103, O111, O145 and O26 inoculated to spinach and soybean sprout

The aim of the present study was to investigate the effect of lactic acid against Shiga toxin producing Escherichia coli (O157:H7 and non-O157 serogroups including O103, O111, O145 and O26) at different conditions. Soybean sprouts and spinach leaves inoculated with each serogroup of E. coli (∼7.00 + 1.00 log₁₀ cfu/g) were treated with the lactic acid solutions at different concentrations (0% (control), 1.5%, 2.0%, or 2.5%) and at different temperatures (20, 40, or 50 °C) for 3 min. Results indicated that regardless of the treatment temperature, no significant reduction in the numbers of any serogroup occurred in the control group (0%) (p > 0.05). However, lactic acid at concentration of 1.5%, 2% and 2.5% was found to be effective against all organisms tested. There was no significant difference (p > 0.05) between E. coli O157:H7 and non-O157 STEC serogroups at any treatment group. The highest reductions (ca. 4.00 log₁₀ cfu/g) of all serotypes in both produces were observed after immersing into 2.5% lactic acid at 50 °C. The results of this study showed that decontamination of fresh produces such as spinach and soybean sprout with lactic acid solutions prepared at mild temperatures (40 °C and 50 °C) might be an effective safety measure in preventing public health risks associated with these products contaminated with STEC.     

Application of artificial neural network to predict Escherichia coli O157:H7 inactivation on beef surfaces

The objective of this study was to develop artificial neural network (ANN) models for quantifying Escherichia coli O157:H7 (E. coli) inactivation due to low-voltage electric current on beef surfaces and to compare them with statistical models for their suitability as a tool for online processing by the meat industry. Modeling techniques with optimal prediction accuracies of E. coli inactivation on meat would not only enhance the meat quality and public perception from a safety perspective, but also improve the marketability of the meat products. The data used in this study were obtained from experiments that measured the percentage (%) of E. coli O157:H7 reduction (output) on beef surfaces when subjected to current (input 1) 300, 600, and 900 mA, duty cycles (input 2) 30, 50, and 70%, and frequency (input 3) 1, 10, and 100 kHz for three treatment times (2, 8, 16 min). Data were subjected to statistical and artificial neural network (ANN) modeling techniques. Data from each input set were sub-partitioned into training, testing, and validation data sets for ANN. Back-propagation (BP) and Kalman filter (KF) learning algorithms were used in ANN to develop nonparametric models between input and output data sets. The trained ANN models were cross-tested with validation data. Various statistical indices including R² between actual and predicted outputs were produced and examined for selecting the best networks. Prediction plots for current, frequencies, and duty cycles indicated that ANN models had better accuracies compared to the statistical models in predicting from unseen pattern. Further, ANN models were able to more robustly generalize and interpolate unseen patterns within the domain of training. Since ANN models have the inherent ability to handle high biological variability and the uncertainty associated with inactivation of microorganisms, they have great potential for meat quality evaluation and monitoring in meat industry.     

Antimicrobial activity of essential oils against Escherichia coli O157:H7 in organic soil

Soil can be a significant source of preharvest contamination of produce by pathogens. Demand for natural pesticides such as essential oils for organic farming continues to increase. We examined the antimicrobial activity of several essential oils against Escherichia coli O157:H7 in soil. Two essential oils (cinnamaldehyde and eugenol), two bio-pesticides (Ecotrol and Sporan) containing essential oils, and an organic acid (acetic acid) at 0.5%, 1.0%, 1.5% and 2.0%, were mixed with organic sandy soil and inoculated with five different strains of E. coli O157:H7. Soils were incubated at room temperature (22 °C) and samples obtained at 1, 7 and 28 days were enumerated to determine survival. E. coli O157:H7 populations in soil were reduced by up to 5 log cfu/g after 24 h incubation at room temperature with 2% cinnamanaldehyde, Ecotrol, Sporan or vinegar. Reduction in E. coli O157:H7 by eugenol was not significantly different from control. Overall, E. coli O157:H7 strain 4406 was the most sensitive of all the five strains tested and cinnamaldehyde was superior to other treatments in reducing E. coli O157:H7 in soil. In general, increases in essential oil concentrations corresponded to reduced survival of E. coli O157:H7 with all oils used in this study. The results suggest that oils can reduce potential contamination of fresh organic produce inadvertently contaminated by soil.     

Combined treatment with silver ions and organic acid enhances growth-inhibition of Escherichia coli O157:H7

Individual and combined treatment with silver ions and selected organic acids were evaluated for growth-inhibition of Escherichia coli O157:H7. The concentrations of silver ion were 0.1, 0.3, 0.5, and 1.0 ppm and, citric, lactic, maleic, succinic, and tartaric acids (0.05% and 0.1%) were used. The inhibitory effect was measured during the growth of E. coli O157:H7 in LB broth by optical density at 600 nm. For individual treatments, silver ion at all concentrations and organic acids at 0.1% had a stronger inhibitory effect than untreated control and 0.05% organic acid treatments. For combined treatments, 1.0 ppm of silver ion with 0.1% of organic acids had the greatest inhibitory effect on E. coli O157:H7 growth. With different concentrations, combination with 1.0 ppm of silver ion and 0.05% of organic acids showed greater inhibitory effect than combination with 0.3 ppm of silver ion and 0.1% of organic acids. Combined treatment with silver ion and organic acid showed the enhanced inhibitory effect of E. coli O157:H7 compared to individual treatments. The present study indicated that growth-inhibiting effect of combined treatment was dependant on the concentration of silver ion rather than that of organic acid.     

Inactivation of Escherichia coli O157:H7 in vitro and on the surface of spinach leaves by biobased antimicrobial surfactants

This study was conducted to evaluate the effect of biosurfactants on the populations of Escherichia coli O157:H7 in suspension and on spinach leaves. Eight surfactants including four soybean oil-based biosurfactants, sodium dodecyl sulfate (SDS), polyoxyethylene sorbitan monooleate (Tween 80), sophorolipid (SO) and thiamine dilauryl sulfate (TDS) at concentrations of 0.1%, 0.5% and 1.0% were tested in bacterial suspension, and the most effective biosurfactants were applied on spinach leaves. Results showed that the soybean oil-based biosurfactants, SDS or Tween 80 did not significantly affect E. coli O157:H7 populations. SO and TDS at concentrations of 1.0% were effective in reducing E. coli O157:H7 populations in bacterial suspension. E. coli O157:H7 with an initial population of 7.1 log CFU/mL was not detectable (detection limit: 1 log CFU/mL) after 1 min in 1.0% TDS or after 2 h in 1.0% SO. On spinach leaves, SO at 1% did not significantly affect E. coli when compared to a water wash during 7 days post-treatment storage at 4 °C. However, TDS (1.0%) wash was as effective as 200 ppm chlorine in reducing population of spot inoculated E. coli O157:H7, achieving 3.1 and 2.7 log CFU/per leaf at day 0, and 1.4 and 1.9 log CFU/leaf at day 7 when compared with a water wash. No apparent change in spinach visual quality was observed. None of treatments caused changes in visual quality of spinach. Electron micrographs suggested ultrastructural damage of bacterial cells such as separation of the outer membrane from the cytoplasmic membrane. Overall, our results showed that SO and TDS may be potential sanitizers in inactivating human pathogens such as E. coli O157:H7 in wash water and on fresh produce.     

Effect of combined ozone and organic acid treatment for control of Escherichia coli O157:H7 and Listeria monocytogenes on enoki mushroom

This study evaluated the effects of ozonated water (1, 3, and 5 ppm) alone with different exposure times (0.5, 1, 3, or 5 min), and combinations of 3 ppm ozone with 1% organic acids (acetic, citric, or lactic acids) during 5-min exposure for control of Escherichia coli O157:H7 and Listeria monocytogenes on enoki mushroom and to observe the regrowth of these pathogenic bacteria on treated enoki mushroom during storage for 10 days at 15 °C. Results showed that ozone treatment gave less than 1.0- and 0.5-log count reductions on E. coli O157:H7 and L. monocytogenes, respectively. Efficacy was improved with combined 3 ppm ozone and 1% citric acid treatment, resulting in 2.26- and 1.32-log count reductions, respectively. During storage at 15 °C (10 days) after combined treatment and packaging, populations of E. coli O157:H7 and L. monocytogenes increased to more than 8.0 log cfu/g, indicating that the combined treatment did not have a residual antimicrobial effect during storage. Although the storage study did not show control of these pathogens, the combined ozone–organic acid treatment was more effective than individual treatments in reducing initial population levels of these pathogens on enoki mushroom.     

Combined effects of heat,acetic acid,and salt for inactivating Escherichia coli O157:H7 in laboratory media

Heat, acid, and salt have been commonly used to ensure the microbial safety of foods and are often used in combinations in many food products. When combined, they can produce different results, such as additive, synergistic, and antagonistic effects. However, there has been little investigation into the effect of these combination treatments. Therefore, in this study, the effect of combined treatment of heat, acid, and salt was investigated in laboratory media. All possible paired combinations among three factors, heat (55 °C), acid (0.25% acetic acid, [v/v]) and salt (3%, [w/v]) were tested and compared with individual treatments for killing E. coli O157:H7 in laboratory media. When salt was combined with heat, there was no significant difference in reduction of E. coli O157:H7 (additive effect). However, when acid was combined with heat, there was a higher reduction of E. coli O157:H7 (synergistic effect). When salt was combined with acid treatment, salt gave protection against acid treatment (antagonistic effect), thus, there was lower reduction of E. coli O157:H7 in the combined treatment than in the single acid treatment. Depending on the combination of preserving factors, results were different.     

Effect of pomegranate powder on the heat inactivation of Escherichia coli O104:H4 in ground chicken

Health concerns have led to a search for natural plant-based antimicrobials. Ellagic acid has been shown to have antimicrobial activity against foodborne pathogens. The objective of this study was to assess the effect of a high-ellagic acid commercial pomegranate on the heat resistance of Escherichia coli O104:H4 in ground chicken. A full 2⁴ factorial design was used, consisting of temperature treatment with four levels (55.0, 57.5, 60.0, and 62.5 °C) and pomegranate with four levels (0.0, 1.0, 2.0, and 3.0 wt/wt. % containing 70% ellagic acid). Experiments were conducted twice, providing a total of 32 survival curves. A three-parameter Weibull primary model was used to describe survival kinetics. Secondary models were then developed to estimate the shape parameter β (i.e., curvature representing susceptibility of cells to stress), scale parameter γ (i.e., time to reach the first decimal reduction) and the 5.0-log lethality time t_5.0 (i.e., time to reach a 5.0-log reduction), all as polynomial functions of temperature and pomegranate powder concentration. The positive effect of pomegranate concentration on both β and γ demonstrated that the phenolic-rich pomegranate powder causes E. coli O104:H4 cells to become more susceptible to heat, increasing the steepness and concavity of the isothermal survival curves. It was estimated that the 5.0-log reduction time would reach a minimum at a pomegranate powder concentration of 1%, producing a 50% decrease in lethality time, in comparison to that without added pomegranate powder. Nonetheless, a mixed-effect omnibus regression further confirmed that the greatest difference in the thermal resistance of E. coli O104:H4 happened between tests with and without pomegranate powder. In fact, adding more than 1.0% pomegranate powder, at a constant temperature, resulted only in a marginal decrease in thermal resistance. Meat processors can use the model to design lethality treatments in order to achieve specific reductions of E. coli O104:H4 in ground chicken.     

Effects of culture conditions on the subsequent heat inactivation of E. coli O157:H7 in apple juice

Escherichia coli O157:H7 cells were grown in various acidic growth media including an acidogenic nutrient broth (NB) supplemented with 1% glucose (NBG) and NB acidified to pH 4.5 with 0.25% citric or malic acids. The pH in NBG continuously decreased, reaching a final pH of 4.46 after 28 h. The pH in the control culture (NB) did not significantly change throughout the incubation. When heated in apple juice at 55 °C, cells grown in NBG had the significantly highest D₅₅ value (250 ± 39.67 s). Thermal inactivation rates established for cells grown in NB, citric acid- and malic acid-acidified NBs were 51.39 ± 1.34, 25.46 ± 1.21, and 45.42 ± 0.36 s, respectively. When compared with the D₅₅ values of cells previously exposed to combinations of environmental stress factors, cells grown in NBG were also found to be significantly heat resistant and were deemed appropriate to be used in heat challenge studies.     

Cloth-based hybridization array system for the identification of Escherichia coli O157:H7

A simple cloth-based hybridization array system (CHAS) utilizing polyester cloth as the solid phase for DNA hybridizations has been adapted as a tool for the identification of presumptive verotoxigenic Escherichia coli O157:H7 colonies isolated from foods by standard culture techniques. Key indicator genes for this organism, rfbO157, fliCH7, vt1 and vt2 (encoding the O and flagellar antigenic determinants and verotoxin genes, respectively) were amplified in a multiplex PCR incorporating digoxigenin-dUTP, followed by hybridization of the amplicons with an array of specific oligonucleotide probes immobilized on polyester cloth, and subsequent immunoenzymatic assay of the bound digoxigenin label. This system includes a simple internal amplification control (IAC) to gauge PCR inhibition based on the incorporation of a primer pair with complementary 3′ ends, resulting in the generation of a unique “primer-dimer” detectable by hybridization with a specific capture probe immobilized on polyester cloth. The CHAS provided sensitive and specific detection of the E. coli O157:H7gene markers, exhibiting the expected patterns of reactivity with a panel of various target and non-target organisms.     

Adherence of cold-adapted Escherichia coli O157:H7 to stainless steel and glass surfaces

The effects of previous cold-induced cell elongation on adherence of Escherichia coli O157:H7 to glass slides and stainless steel surfaces was evaluated at 4 °C for ≤48 h. Planktonic E. coli O157:H7 with and without cold adaptation were prepared at 15 and 37 °C, respectively, and planktonic E. coli O157:H7 containing elongated (>4 ≤ 10 μm) and filamentous (>10 μm) cells were prepared at 6 °C. Despite morphological differences in planktonic E. coli O157:H7 preparations, all three cell types attached to a greater extent to glass than to the stainless steel surfaces. E. coli O157:H7 cells adapted to growth at 15 °C attached better to both glass and stainless steel surfaces (3.2 and 2.6 log cfu/cm², respectively) than cells of the other treatments at ≥24 h. Cells adapted at 6 °C attached to glass slides and stainless steel coupons at levels of 3.0 and 1.8 log cfu/cm², respectively, while E. coli O157:H7 cells grown at 37 °C attached to these surfaces at levels of 2.0 and 1.7 log cfu/cm², respectively. No further attachment of cells from any of the treatments was noted between 24 and 48 h at 4 °C. These results suggest that E. coli O157:H7 cells adapted at 6 °C–15 °C have greater potential to attach to food contact surfaces than those grown at higher temperature. The enhanced biofilm-forming ability of 6 °C or 15 °C-adapted, elongated and filamentous E. coli O157:H7 cells did not appear to be related to the greater entanglement of longer cells within biofilm matrices.     

Effects of UV-C treatment on inactivation of Salmonella enterica and Escherichia coli O157:H7 on grape tomato surface and stem scars,microbial loads,and quality

The purpose of this study was to investigate the effectiveness of ultraviolet-C (UV-C) light inactivation as affected by the location of pathogens on the surface and at stem scars of whole grape tomatoes. A mixed bacterial cocktail containing a three strain mixture of Escherichia coli O157:H7 (C9490, E02128 and F00475) and a three serotype mixture of Salmonella enterica (S. Montevideo G4639, S. Newport H1275, and S. Stanley H0558) were used. Tomatoes were spot inoculated using approximately 100 μL of inocula to achieve a population of about 10^7±1 CFU/tomato. Additionally, the effects of treatment on color, texture, lycopene content, and background microbial loads during post UV-C storage at 4 °C for 21 days were determined. Results showed that UV-C doses of 0.60–6.0 kJ/m² resulted in 2.3–3.5 log CFU per fruit reduction of E. coli O157:H7 compared to 2.15–3.1 log CFU per fruit reduction for Salmonella on the surfaces. Under the same conditions, log reductions achieved at stem scar were 1.7–3.2 logs CFU for E. coli O157:H7 and 1.9–2.8 logs CFU for Salmonella. The treatment was effective in controlling native microbial loads during storage at 4 °C as the total aerobic mesophilic organisms (PCA) and anaerobic lactic acid bacteria (LAB) counts of treated tomatoes were significantly (p < 0.05) lower during storage compared to the control group and the yeast and mold populations were reduced significantly below the detection limit. Furthermore, the firmness of tomato and its color was not affected by the UV-C doses during storage. UV-C radiation could potentially be used for sanitizing fresh tomatoes and extending shelf-life. The results of this study indicate that the specific location of pathogens on the produce influences the effectiveness of UV-C treatment, which should be taken into consideration for the design of UV-C systems for produce sanitization.     

Modeling the inactivation of Escherichia coli O157:H7 and Uropathogenic E. coli in ground beef by high pressure processing and citral

Escherichia coli O157:H7 are a well-known intestinal foodborne pathogen which were responsible for numerous foodborne illness outbreaks. Uropathogenic E. coli (UPEC) are common contaminants in meat and poultry, and may cause urinary tract infections after colonizing the gastrointestinal tract followed by accidental transfer of contaminated feces from the anus to the urethra. High pressure processing (HPP) has been demonstrated an effective means in reducing pathogenic E. coli levels in meat and poultry. Citral, an antimicrobial, also demonstrated some inactivation effect on pathogenic E. coli in ground beef (ca. 0.5–1.0 log CFU/g reduction at 1% w/w without HPP). With HPP alone, to achieve 5 log CFU/g reduction required a 500 MPa level and 15 min (for both O157:H7 and UPEC). However, 1% of citral addition may lower the pressure requirement to 380 MPa and 15 min which could reduce the food quality damage. To effectively inactivate E. coli O157:H7 and UPEC in meat, high pressure processing (HPP) in combination with the antimicrobial citral was studied. Ground beef inoculated with E. coli O157:H7 or UPEC were treated at different HPP conditions (250–350 MPa; 10–20 min), and citral (0.75–1.25%, w/w) following a central composite experimental design. Quadratic linear regression equations were developed to describe and predict the reductions of E. coli O157:H7 (R² = 0.93, p < 0.001) and UPEC (R² = 0.92, p < 0.001). Dimensionless nonlinear models consisting of three impact factors were also developed and compared with the linear models. These models were experimentally validated. Citral enhanced the inactivation of pathogenic E. coli, increasing the effectiveness of the HPP process. The models may assist the food industry and regulatory agencies in risk assessment of E. coli O157:H7 and UPEC on ground meats.     

Sublethal injury and recovery of Escherichia coli O157:H7 by high pressure carbon dioxide

A study was carried out to investigate possible sublethal injury caused by high pressure carbon dioxide (HPCD) to Escherichia coli O157:H7 suspended in phosphate-buffered saline (PBS, pH 7.00). The treatment pressure was 5 MPa, treatment temperatures were 25–37 °C and treatment time was 5–70 min. Only 1.21 log₁₀ cycles reduction was obtained in the nonselective medium, while a higher reduction of 5.18 log₁₀ cycles was obtained in the selective medium after treatment at 5 MPa and 25 °C for 50 min, indicating HPCD could induce sublethal injury of E. coli cells and these cells could not recover in the selective medium. The proportion of the sublethally injured E. coli cells in the survivors increased dramatically up to 72.4% with increasing the treatment time from 20 min to 30 min by HPCD at 5 MPa and 25 °C, and this proportion increased gradually with increasing the treatment time, up to 100% at 5 MPa and 25 °C for 60 min. The effect of recovery media, inhibitors of specific metabolic processes, Mg and Ca cations on the recovery of the sublethally injured cells was also investigated. When PBS, peptone water, tryptic soy broth (TSB) and carrot juice were used as recovery media, the maximum repair rate of the sublethally injured cells was found in TSB and the minimum was in PBS. The addition of inhibitors such as sodium azide, chloramphenicol, rifampicin and penicillin G showed that repair of most sublethally injured cells required energy, protein and RNA synthesis, but was not dependent on peptidoglycan synthesis. Moreover, Mg and Ca cations were also needed in the repair.     

Kinetics of Escherichia coli inactivation employing hydrogen peroxide at varying temperatures,pH and concentrations

The effectiveness of hydrogen peroxide on the destruction of planktonic cells of Escherichia coli at different temperatures, pH and sanitizer concentrations was studied. Inactivation kinetics of E. coli exhibited a clear dependence on hydrogen peroxide concentration, pH and temperature. A Weibullian mathematical model successfully described the inactivation curves. Quantitative kinetic results obtained allowed to identify various combinations H₂O₂ concentration–pH–temperature for 5-log cycles reduction of E. coli. Flow cytometry analysis revealed induced H₂O₂ cytoplasm membrane damage. TEM observations indicated that H₂O₂ treatment resulted in rupture of outer and cytoplasm membranes and a more uniform granularity.     

Antimicrobial activity of mustard essential oil against Escherichia coli O157:H7 and Salmonella typhi

The aim of this study was to investigate how mustard essential oil (EO) affected the cell membrane of Escherichia coli O157:H7 and Salmonella typhi. Intracellular pH and ATP concentration and the release of cell constituents were measured when mustard EO was in contact with E. coli and S. typhi at its minimal inhibitory concentration (MIC) and maximal tolerated concentration (MTC). The treatment with mustard EO affected the membrane integrity of bacteria and induced a decrease of the intracellular ATP concentration. Also, the extracellular ATP concentration increased and a reduction of the intracellular pH was observed in both bacteria. A significantly (P ? 0.05) higher release of cell constituent was observed when both bacteria cells were treated with mustard EO. Electronic microscopy observations showed that the cell membranes of both bacteria were apparently damaged by mustard EO. In conclusion, mustard EO affects the concentration of intracellular component, such as ATP in both bacteria and affects the pH suggesting that cytoplasmic membrane is involved in the antimicrobial action of mustard EO. Mustard EO can be used as an effective antimicrobial agent. We have demonstrated that mustard EO affected the cell membrane integrity, resulting in a loss of cell homeostasis.     

Development of an immunomagnetic separation method for efficient enrichment of Escherichia coli O157:H7

Immunomagnetic separation uses antibody-coated paramagnetic particles to selectively bind and purify the target organisms from a comprehensive range of complex food matrices. Aim of this study was to develop and optimize an immunomagnetic separation method based on monoclonal antibody for efficient isolation of Escherichia coli O157:H7 in food samples. The key parameters for preparing the immunomagnetic beads; the coupling rate between monoclonal antibody and magnetic beads, additive amount of immunomagnetic beads, and magnetic separation times were optimized with different concentrations of E. coli O157:H7. Under optimized conditions, the capture efficiency (CE) was greater than 98% against 10¹–10⁶ cells of E. coli O157:H7 with 0.05 mg immunomagnetic beads. The immunomagnetic beads exhibited high specific binding with E. coli O157:H7 strains (CE > 98%), and low binding with non-target bacteria (CE < 2%) except for S. aureus (CE = 23.6%). The capture efficiency of immunomagnetic beads against E. coli O157:H7 in ground beef and milk samples were 94.4% and 99.8%, respectively.