Inactivation of Escherichia coli and Listeria innocua in kiwifruit and pineapple juices by high hydrostatic pressure

Escherichia coli and Listeria innocua in kiwifruit and pineapple juices were exposed to high hydrostatic pressure (HHP) at 300 MPa for 5 min. Both bacteria showed equal resistance to HHP. Using low (0 degrees C) or sub-zero (-10 degrees C) temperatures instead of room temperature (20 degrees C) during pressurization did not change the effectiveness of HHP treatment on both bacteria in studied juices. Pulse pressure treatment (multiple pulses for a total holding time of 5 min at 300 MPa) instead of continuous (single pulse) treatment had no significant (p>0.05) effect on the microbial inactivation in kiwifruit juice; however, in pineapple juice pulse treatment, especially after 5 pulses, increased the inactivation significantly (p<0.05) for both bacteria. Following storage of pressure-treated (350 MPa, 20 degrees C for 60 s x 5 pulses) juices at 4, 20 and 37 degrees C up to 3 weeks, the level of microbial inactivation further increased and no injury recovery of the bacteria were detected. This work has shown that HHP treatment can be used to inactivate E. coli and L. innocua in kiwifruit and pineapple juices at lower pressure values at room temperature than the conditions used in commercial applications (>400 MPa). However, storage period and temperature should carefully be optimized to increase the safety of HHP treated fruit juices.     

Thermal inactivation of stationary-phase and acid-adapted Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in fruit juices

The heat resistance of stationary-phase and acid-adapted Escherichia coli O157:H7, Salmonella enterica (serotypes Typhimurium, Enteritidis, Gaminara, Rubislaw, and Hartford), and Listeria monocytogenes was evaluated in single-strength apple. orange, and white grape juices adjusted to pH 3.9. The heat resistance increased significantly (P < 0.05) after acid adaptation. Salmonella had an overall lower heat resistance than the other pathogens. Acid-adapted E. coli O157:H7 presented the highest heat resistance in all juices at the temperatures tested, with lower z-values than Salmonella and L. monocytogenes. The heat resistance (D(60 degrees C)-values) of all three pathogens, assessed in tryptic soy broth adjusted to different pH values, increased above pH 4.0. From the results obtained in this study, one example of a treatment that will inactivate 5 logs of vegetative pathogens was calculated as 3 s at 71.1 degrees C (z-value of 5.3 degrees C). Normal processing conditions calculated for hot-filled, shelf-stable juices achieve a lethality in excess of 50,000 D for all three pathogens.     

Inactivation of Escherichia coli O157:H7 in fruit juices by combined treatments of citrus fruit essential oils and heat

This work approaches the possibility of combining mild heat treatments with citrus fruit essential oils (EOs) to improve the effectiveness of heat treatments and thus to reduce treatment intensity. Concentrations between 10 and 200μL/L of lemon, mandarin, or orange EO were tested at 54°C for 10min in laboratory media, determining that 200μL/L of each EO was necessary to achieve a 5 log(10) reduction of the initial Escherichia coli O157:H7 concentration. A relationship could be established between sublethally injured cells after the heat treatment and inactivated cells after the combined process. In apple juice, the synergism in the inactivation of E. coli O157:H7 when adding 200μL/L of lemon EO might suppose a reduction in the treatment temperature (of 4.5°C) or in the treatment time (by 5.7 times) within the range of temperature assayed (54-60°C). Addition of 75μL/L of lemon EO was determined to achieve the same synergistic effect of the combined treatment when the initial inoculum was reduced from 3×10(7) to 3×10(4)CFU/mL. Since the addition of lemon EO did not decrease the hedonic acceptability of apple juice, the proposed combined treatment could be further studied and optimized for the production of new minimally processed juices.     

Antimicrobial activity of clove and cinnamon essential oils against Listeria monocytogenes in pasteurized milk

The antimicrobial activity of essential oils (EOs) of cinnamon bark, cinnamon leaf, and clove against Listeria monocytogenes Scott A were studied in semiskimmed milk incubated at 7 degrees C for 14 days and at 35 degrees C for 24 h. The MIC was 500 ppm for cinnamon bark EO and 3,000 ppm for the cinnamon leaf and clove EOs. These effective concentrations increased to 1,000 ppm for cinnamon bark EO, 3,500 ppm for clove EO, and 4,000 ppm for cinnamon leaf EO when the semiskimmed milk was incubated at 35 degrees C for 24 h. Partial inhibitory concentrations and partial bactericidal concentrations were obtained for all the assayed EOs. The MBC was 3,000 ppm for the cinnamon bark EO, 10,500 ppm for clove EO, and 11,000 ppm for cinnamon leaf EO. The incubation temperature did not affect the MBC of the EOs but slightly increased the MIC at 35 degrees C. The increased activity at the lower temperature could be attributed to the increased membrane fluidity and to the membrane-perturbing action of EOs. The influence of the fat content of milk on the antimicrobial activity of EOs was tested in whole and skimmed milk. In milk samples with higher fat content, the antimicrobial activity of the EOs was reduced. These results indicate the possibility of using these three EOs in milk beverages as natural antimicrobials, especially because milk beverages flavored with cinnamon and clove are consumed worldwide and have been increasing in popularity in recent years.     

Antimicrobial activity of Viburnum opulus fruit juices and extracts

The antimicrobial activities of fruit juices and ethanol extracts of Viburnum opulus L. genotypes were compared in this study. These activities were tested against human pathogenic microorganisms using the agar well diffusion method. A total of ten Gram-positive and Gram-negative bacterial cultures, as well as nine yeast strains, were used for the investigation. The most effective antibacterial activity was exhibited by the fruit juices against Salmonella typhimurium, Salmonella agona, and Listeria monocytogenes, with inhibition zones of 23.6, 20.7, and 19.1 mm, respectively. Staphylococcus epidermidis and Micrococcus luteus displayed the highest resistance, with minimal inhibition zones of 14.2 and 15.0 mm, respectively. The fruit juices showed greater antibacterial activity compared to the ethanol extracts. In contrast, the growth of the yeast cultures exhibited little or no sensitivity to the fruit juices and ethanol extracts. The conclusion of this study is that V. opulus fruits are potential antibacterial remedies.     

Survival of Escherichia coli O157:H7, Salmonella enteritidis, Staphylococcus aureus, and Listeria monocytogenes in Kimchi

The survival of gram-positive and gram-negative foodborne pathogens in both commercial and laboratory-prepared kimchi (a traditional fermented food widely consumed in Japan) was investigated. It was found that Escherichia coli O157:H7, Salmonella Enteritidis, Staphylococcus aureus, and Listeria monocytogenes could survive in both commercial and laboratory-prepared kimchi inoculated with these pathogens and incubated at 10 degrees C for 7 days. However, when incubation was prolonged, the S. aureus level decreased rapidly from the initial inoculum level to the minimum detectable level within 12 days, whereas Salmonella Enteritidis and L. monocytogenes took 16 days to reach similar levels in commercial kimchi. On the other hand, E. coli O157:H7 remained at high levels throughout the incubation period. For laboratory-prepared kimchi, the S. aureus level decreased rapidly from the initial inoculum level to the minimum detectable level within 12 days, and L. monocytogenes took 20 days to reach a similar level. E. coli O157:H7 and Salmonella Enteritidis remained at high levels throughout the incubation period. The results of this study suggest that the contamination of kimchi with E. coli O157:H7, Salmonella Enteritidis, S. aureus, or L. monocytogenes at any stage of production or marketing could pose a potential risk.     

Antimicrobial activity of plant extracts against Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes on fresh lettuce

Plant extracts have been found to be effective in reducing microorganisms. This study evaluated antimicrobial activity of 12 plant extracts against Salmonella Typhimurium, Escherichia coli O157:H7, and Listeria monocytogenes by using a disk diffusion assay, and Syzygium aromaticum (clove) showed the highest inhibitory effect. To investigate the efficacy of clove extract that inactivates pathogens on lettuce, inoculated lettuce with S. Typhimurium, E. coli O157:H7, and L. monocytogenes was treated with diluted clove extracts or distilled water for 0, 1, 3, 5, and 10 min. Clove extract treatment significantly reduced populations of the 3 tested pathogens from the surface of lettuce. Practical Application: This result indicated that clove extract is a useful antimicrobial agent to reduce the microbial level of foodborne pathogens on fresh lettuce. It also might be a natural antimicrobial for reducing or replacing chemical sanitizers in food preservation.     

Antimicrobial effects of alginate-based films containing essential oils on Listeria monocytogenes and Salmonella typhimurium present in bologna and ham

Bologna and ham slices (300 of each) were inoculated with Salmonella Typhimurium or Listeria monocytogenes at 10(3) CFU/cm(2). Alginate-based edible films that had been immersed in a 2 or 20% (wt/vol) CaC12 solution and contained 1% (wt/ vol) essential oils of Spanish oregano (O; Corydothymus capitatus), Chinese cinnamon (C; Cinnamomum cassia), or winter savory (S; Satureja montana) were then applied to slices to control pathogen growth. On bologna, C-based films pretreated with 20% CaC12 were the most effective against the growth of Salmonella Typhimurium and L. monocytogenes. L. monocytogenes was the more sensitive bacterium to O-, C-, and S-based films. L. monocytogenes concentrations were below the detection level (<10 CFU/ml) after 5 days of storage on bologna coated with O-, C-, or S-based films pretreated with 20% CaCl2. On ham, a 1.85 log CFU/cm2 reduction of Salmonella Typhimurium (P < 0.05) was found after 5 days of storage with C-based films regardless of the type of pretreatment used (2 or 20% CaC12) or when coated with O-based films pretreated with 20% CaCl2. L. monocytogenes was highly resistant in ham, even in the presence of O-, C-, or S-based films. However, C-based films pretreated with 20% CaCl2 were the most effective against the growth of L. monocytogenes. Evaluation of the availability of active compounds in films revealed a significantly higher release of active compounds in C-based films (P < 0.05) regardless of pretreatment or meat tested (bologna or ham). O-based films had the lowest release level of active compounds. The release of active compounds from O- and S-based films pretreated with 20% CaCl2 was faster than that in the same respective films pretreated with 2% CaCl2 regardless of the meat type. C-based film pretreated by immersion in a 20% CaCl2 solution was most efficient against both pathogens, and migration of active compounds was higher in C-based films than in O- and S-based films.     

Bactericidal activities of plant essential oils and some of their isolated constituents against Campylobacter jejuni,Escherichia coli,Listeria monocytogenes,and Salmonella enterica

An improved method of sample preparation was used in a microplate assay to evaluate the bactericidal activity levels of 96 essential oils and 23 oil compounds against Campylobacter jejuni, Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella enterica obtained from food and clinical sources. Bactericidal activity (BA50) was defined as the percentage of the sample in the assay mixture that resulted in a 50% decrease in CFU relative to a buffer control. Twenty-seven oils and 12 compounds were active against all four species of bacteria. The oils that were most active against C. jejuni (with BA50 values ranging from 0.003 to 0.009) were marigold, ginger root, jasmine, patchouli, gardenia, cedarwood, carrot seed, celery seed, mugwort, spikenard, and orange bitter oils; those that were most active against E. coli (with BA50 values ranging from 0.046 to 0.14) were oregano, thyme, cinnamon, palmarosa, bay leaf, clove bud, lemon grass, and allspice oils; those that were most active against L monocytogenes (with BA50 values ranging from 0.057 to 0.092) were gardenia, cedarwood, bay leaf, clove bud, oregano, cinnamon, allspice, thyme, and patchouli oils; and those that were most active against S. enterica (with BA50 values ranging from 0.045 to 0.14) were thyme, oregano, cinnamon, clove bud, allspice, bay leaf, palmarosa, and marjoram oils. The oil compounds that were most active against C. jejuni (with BA50 values ranging from 0.003 to 0.034) were cinnamaldehyde, estragole, carvacrol, benzaldehyde, citral, thymol, eugenol, perillaldehyde, carvone R, and geranyl acetate; those that were most active against E. coli (with BA50 values ranging from 0.057 to 0.28) were carvacrol, cinnamaldehyde, thymol, eugenol, salicylaldehyde, geraniol, isoeugenol, citral, perillaldehyde, and estragole; those that were most active against L monocytogenes (with BA50 values ranging from 0.019 to 0.43) were cinnamaldehyde, eugenol, thymol, carvacrol, citral, geraniol, perillaldehyde, carvone S, estragole, and salicylaldehyde; and those that were most active against S. enterica (with BA50 values ranging from 0.034 to 0.21) were thymol, cinnamaldehyde, carvacrol, eugenol, salicylaldehyde, geraniol, isoeugenol, terpineol, perillaldehyde, and estragole. The possible significance of these results with regard to food microbiology is discussed.     

Antimicrobial activity of epsilon-polylysine against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in various food extracts

ABSTRACT:  This study compared the antimicrobial effects of ɛ-polylysine (ɛ-PL) against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes in 6 food extracts and in broth. The food extracts (10% (w/w) in distilled water) evaluated were fat-free and whole fat milk, beef, bologna, rice, and vegetables (50:50 ratio of broccoli and cauliflower). ɛ-PL was tested at 0.005% and 0.02% (w/v) against E. coli O157:H7 and L. monocytogenes , and 0.02% and 0.04% (w/v) against S. Typhimurium . The substrates were inoculated (5 log CFU/mL) and periodically analyzed for surviving populations during storage at 12 °C for 6 d. In general, all 3 pathogens reached 7 to 9 log CFU/mL within 2 d in control substrates (no ɛ-PL). Immediate bactericidal effects ( P < 0.05) following exposure to ɛ-PL were obtained in the rice (all pathogens) and vegetable ( E. coli O157:H7 and S. Typhimurium ) extracts. During storage, antimicrobial effects of ɛ-PL were more pronounced in the food extracts than in the broth medium. The greatest antimicrobial activity for all 3 pathogens was obtained in the rice and vegetable extracts, where counts were reduced ( P < 0.05) to below the detection limit (0.0 log CFU/mL) by one or both ɛ-PL concentrations tested. In the other food extracts (fat-free milk, whole fat milk, beef, and bologna), both ɛ-PL concentrations tested generally resulted in lower ( P < 0.05) pathogen levels at the end of storage compared to initial counts, with better bactericidal effects exerted by the higher of the 2 ɛ-PL concentrations. Additional research is needed to explore the potential antimicrobial effects of ɛ-PL in real food systems.     

Anti yeast activities of some essential oils in growth medium, fruit juices and milk

The anti-yeast activities of four essential oils (EOs) from clary sage, juniper, lemon and marjoram against wild-type isolates of the food-related yeasts Geotrichum candidum, Pichia anomala, Saccharomyces cerevisiae and Schizosaccharomyces pombe in malt extract (ME) medium, apple juice and milk were investigated. Minimal inhibitory concentrations (MICs) for the EOs and their main components were determined and the checkerboard method was used to calculate fractional inhibitory concentration (FIC) indices for the combinations of EOs or components. The most sensitive yeast was S. pombe (MICs of 0.0625-0.125 μl/ml) while G. candidum proved to be the most insensitive (MICs of 0.5-2 μl/ml). In general, the lag phases were lengthened by increasing EO concentrations, while significant reduction of growth rates was obtained only at the highest EO concentrations. The anti-yeast effects of the EOs were good in the acidic pH range optimal for yeasts growth. Combinations of juniper and clary sage EOs resulted in additive effects in the case of S. cerevisiae and G. candidum, but all other combinations showed no interaction. The combination of α-pinene and limonene led to synergism, while the combination of α-pinene with linalool resulted in an additive effect. Cloudy apple juice protected the yeasts against the effect of lemon EO: the lag phases were shorter and the growth rates higher than in clear apple juice. Lemon EO decreased the growth rate of G. candidum in skimmed milk in a dose-independent manner. Our results show that by adding lemon EO to clear apple juice a new, harmonic taste can be achieved and open storage time could be prolonged.     

Antimicrobial and antioxidant activity of spice essential oils

Essential oils of anise, bastard cardamom, cinnamon, dill, mace, zedoary, prikhom, and bitter ginger were determined for their antimicrobial and antioxidant activities. Of all, cinnamon oil had the highest antibacterial activity. The most sensitive bacteria was Bacillus cereus (0.5mg/mL minimum inhibitory concentration, MIC). Anise, cinnamon, dill, and prikhom exhibited strong antifungal activity against Rhodotorula glutinis, Aspergillus ochraceus, and Fusarium moniliforme. Two oil combinations: i) cinnamon and mace oils and ii) cinnamon and prikhom oils showed a synergistic effect against Staphylococcus aureus, Pseudomonas fluorescens, and Salmonella Rissen (0.32–0.38 mg/mL fractional inhibitory concentration index, FICI). Cinnamon, mace, and prikhom oils had strong antioxidant activity with 0.29–5.66 mg/mL IC₅₀, 61.46–68.52% antioxidant activity, 0.22–2.19 mM/mg reducing capacity, and 78.28–84.30% inhibition by 2,2-diphenyl-1-picrylhydrazyl (DPPH), β-carotene bleaching, ferric reducing (FRAP), and superoxide anion scavenging activity assays, respectively. These oils contained high amount of total phenolics (51.54–140.9 μg gallic acid equivalents/mg oil).     

Antimicrobial activity of camel's milk against pathogenic strains of Escherichia coli and Listeria monocytogenes

The inhibitory activity of camel's milk and colostrum at 4°C and 20°C was tested by the well diffusion assay against six pathogens. The activity was also studied in situ by monitoring the growth of a three-strain mixture of Listeria monocytogenes or Escherichia coli O78:K80 in camel's milk, colostrum or Tryptic Soy Broth (TSB) as function of time. The results of the well diffusion assay show that Bacillus cereus was resistant to the inhibitory activity present in camel's milk and to the colostrum, while L. monocytogenes LMG 13304 and E. coli O78:K80(JB2) were the most sensitive as judged by the diameters of the inhibition zones. The in situ test revealed a typical inhibition pattern of both pathogens in camel's milk samples during 48 h of incubation at both storage temperatures. The colostrum exerted a definite bactericidal activity against E. coli O78:K80 at ambient temperature, and the viable counts decreased to below the detectable level in a 1-mL sample at 48 h, while at the refrigeration temperature, the counts were reduced by 1 and 3 log units compared to the initial inoculum and to the positive control, respectively. The camel's milk and colostrum samples had a bacteriostatic effect against L. monocytogenes during the first 8 h of incubation; thereafter, a tendency to increase was noted in the colostrum at 20°C. Similar experiments were carried out on E. coli O78:K80 in heat-treated camel's or cow's milk and showed that the inhibitory effect of camel's milk was reduced by heat treatment.     

Effect of low-temperature, high-pressure treatment on the survival of Escherichia coli O157:H7 and Salmonella in unpasteurized fruit juices

The destructive effect of high pressure (615 MPa) combined with low temperature (15 degrees C) on various strains of Escherichia coli O157:H7 and various serovars of Salmonella in grapefruit, orange, apple, and carrot juices was investigated. The three-strain cocktail of E. coli O157:H7 (SEA13B88, ATCC 43895, and 932) was found to be most sensitive in grapefruit juice (8.34-log reduction) and least in apple juice (0.41-log reductions) when pressurized at 615 MPa for 2 min at 15 degrees C. Correspondingly, no injured survivor was detected in grapefruit and carrot juices under similar treatment conditions. No Salmonella spp. were detected in a 2-min pressure treatment (615 MPa, 15 degrees C) of grapefruit and orange fruit juices. Except for Enteritidis, all four serovars tested in the present study have viability loss of between 3.92- and 5.07-log reductions when pressurized in apple juice at 615 MPa for 2 min at 15 degrees C. No injured cells were recovered from grapefruit and orange juices, whereas the same treatment demonstrated reduction in numbers of Salmonella serovars Agona and Muenchen in apple juices and to a lesser extent with Typhimurium, Agona, and Muenchen in carrot juice. The present study demonstrated that low-temperature, high-pressure treatment has the potential to inactivate E. coli O157:H7 strains and different Salmonella spp. in different fruit juices.     

Inactivation of Listeria innocua, Salmonella Typhimurium, and Escherichia coli O157:H7 on Surface and Stem Scar Areas of Tomatoes Using In-Package Ozonation

A novel in-package ozonation device was evaluated for its efficacy in inactivating three microorganisms (viz., Listeria innocua, attenuated Salmonella Typhimurium, and Escherichia coli O157:H7) on tomatoes and for its effect on fruit quality. The device produced ozone inside sealed film bags, reaching a concentration of 1,000 ppm within 1 min of activation. The three bacterial cultures were inoculated onto either the smooth surface or the stem scar areas of the tomatoes, which were then sealed in plastic film bags and subjected to in-package ozonation. L. innocua on tomatoes was reduced to nondetectable levels within 40 s of treatment on the tomato surface, with inactivation of ca. 4 log CFU per fruit on the stem scar area. An increase in treatment time did not result in a proportional increase in bacterial reduction. For E. coli O157:H7 and Salmonella, there was little difference (<1 log) in the effectiveness of the system when comparing surface and scar-inoculated bacteria. Both bacteria were typically reduced by 2 to 3 log CFU per fruit after 2- to 3-min treatments. No negative effects on fruit color or texture were observed during a 22-day posttreatment storage study of ozone-treated tomatoes. These results suggest that the three bacteria responded differently to ozonation and that in-package ozonation may provide an alternative to chemical sanitizers commonly used by the industry.     

Effectiveness of electrolyzed acidic water in killing Escherichia coli O157:H7, Salmonella enteritidis,and Listeria monocytogenes on the surfaces of tomatoes

A study was conducted to evaluate the efficacy of electrolyzed acidic water, 200-ppm chlorine water, and sterile distilled water in killing Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes on the surfaces of spot-inoculated tomatoes. Inoculated tomatoes were sprayed with electrolyzed acidic water, 200-ppm chlorine water, and sterile distilled water (control) and rubbed by hand for 40 s. Populations of E. coli O157:H7, Salmonella, and L. monocytogenes in the rinse water and in the peptone wash solution were determined. Treatment with 200-ppm chlorine water and electrolyzed acidic water resulted in 4.87- and 7.85-log10 reductions, respectively, in Escherichia coli O157:H7 counts and 4.69- and 7.46-log10 reductions, respectively, in Salmonella counts. Treatment with 200-ppm chlorine water and electrolyzed acidic water reduced the number of L. monocytogenes by 4.76 and 7.54 log10 CFU per tomato, respectively. This study's findings suggest that electrolyzed acidic water could be useful in controlling pathogenic microorganisms on fresh produce.     

Heat Resistance of Salmonella spp., Listeria monocytogenes, Escherichia coli 0157:H7, and Listeria innocua M1, a Potential Surrogate for Listeria monocytogenes, in Meat and Poultry: A Review

ABSTRACT: The heat-resistance data in meat and poultry for various strains of Salmonella, Listeria monocytogenes , and Escherichia coli O157:H7 as well as Listeria innocua M1 are summarized. Heat resistance of these organisms is affected by many factors. Different strains of the same organism have different responses to heat. Heat resistance can also be influenced by the age of the culture, growth conditions, pH, and numerous other factors. Data from this review may prove useful to processors in validating their times and temperatures for thermal processing of meat and poultry. The obvious gaps in the data will provide researchers opportunities to fill those gaps. In addition, it will encourage the development of surrogates, whether biological or otherwise, that will be able to be used in an actual processing environment.     

D and z Values of Salmonella, Listeria innocua, and Listeria monocytogenes in Fully Cooked Poultry Products

: The D and z values of Salmonella, Listeria innocua, and Listeria monocytogenes were obtained for different ready‐to‐eat poultry products, including chicken, turkey, and duck. The D values of Salmonella, L. innocua, and L. monocytogenes were 151.5 to 0.1 min at 55 to 70°C, and the z values of Salmonella, L. innocua, and L. monocytogenes were 4.9 to 7.0 °C. Significant differences were found for the heat resistance of Salmonella, L. innocua, and L. monocytogenes among turkey, duck, and chicken products, indicating that the kinetic values of a certain pathogen in a specific product should be used for determining process lethality in fully cooked and vacuum‐packaged poultry products during post‐cook heat treatments.     

Antimicrobial Efficacy of Zinc Oxide Quantum Dots against Listeria monocytogenes, Salmonella Enteritidis, and Escherichia coli O157:H7

ABSTRACT:  Zinc oxide quantum dots (ZnO QDs) are nanoparticles of purified powdered ZnO. These were evaluated for antimicrobial activity against Listeria monocytogenes , Salmonella Enteritidis, and Escherichia coli O157:H7. The ZnO QDs were utilized as a powder, bound in a polystyrene film (ZnO-PS), or suspended in a polyvinylprolidone gel (ZnO-PVP). Bacteria cultures were inoculated into culture media or liquid egg white (LEW) and incubated at 22 °C. The inhibitory efficacies of ZnO QDs against 3 pathogens were concentration dependent and also related to type of application. The ZnO-PVP (3.2 mg ZnO/mL) treatment resulted in 5.3 log reduction of L. monocytogenes and 6.0 log reduction of E. coli O157:H7 in growth media after 48 h incubation, as compared to the controls. Listeria cells in the LEW control increased from 3.8 to 7.2 log CFU/mL during 8 d incubation, while the cells in the samples treated with 1.12 and 0.28 mg ZnO/mL were reduced to 1.4 and 3.0 log CFU/mL, respectively. After 8 d incubation, the cell populations of Salmonella in LEW in the presence of 1.12 and 0.28 mg ZnO/mL were reduced by 6.1 and 4.1 log CFU/mL over that of controls, respectively. ZnO powder and ZnO-PVP showed significant antimicrobial activities against all 3 pathogens in growth media and LEW. ZnO-PVP coating had less inhibitory effect than the direct addition of ZnO-PVP. No antimicrobial activities of ZnO-PS film were observed. This study suggested that the application of ZnO nanoparticles in food systems may be effective at inhibiting certain pathogens.