Inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce by chlorine dioxide gas

The purpose of this investigation was to study inactivation kinetics of inoculated Escherichia coli O157:H7 and Salmonella enterica on lettuce leaves by ClO(2) gas at different concentrations (0.5, 1.0, 1.5, 3.0, and 5.0 mg l(-1)) for 10 min and to determine the effect of ClO(2) gas on the quality and shelf life of lettuce during storage at 4 degrees C for 7 days. One hundred microliters of each targeted organism was separately spot-inoculated onto the surface (5 cm(2)) of lettuce (approximately 8-9 log CFU ml(-1)), air-dried, and treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity for 10 min. Surviving bacterial populations on lettuce were determined using a membrane transferring method, which included a non-selective medium followed by a selective medium. The inactivation kinetics of E. coli O157:H7 and S. enterica was determined using first-order kinetics to establish D-values and z-values. The D-values of E. coli and S. enterica were 2.9+/-0.1 and 3.8+/-0.5 min, respectively, at 5.0 mg l(-1) ClO(2) gas. The z-values of E. coli and S. enterica were 16.2+/-2.4 and 21.4+/-0.5 mg l(-1), respectively. A 5 log CFU reduction (recommended by the United States Food and Drug Administration) for E. coli and S. enterica could be achieved with 5.0 mg l(-1) ClO(2) gas for 14.5 and 19.0 min, respectively. Treatment with ClO(2) gas significantly reduced inherent microflora on lettuce and microbial counts remained significantly (p<0.05) lower than the uninoculated control during storage at 4 degrees C for 7 days. However, treatment with ClO(2) gas had a significantly (p<0.05) negative impact on visual leaf quality. These results showed that treatment with ClO(2) gas significantly reduced selected pathogens and inherent microorganisms on lettuce; however, the processing conditions would likely need to be altered for consumer acceptance.     

Inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enterica on strawberries by chlorine dioxide gas

Inactivation kinetics of inoculated Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enterica on strawberries by chlorine dioxide gas at different concentrations (0.5, 1, 1.5, 3 and 5 mgl(-1)) for 10 min were studied. A cocktail of three strains of each targeted organism (100 microl) was spotted onto the surface of the strawberries (approximately 8-9 log ml(-1)) separately followed by air drying, and then treated with ClO(2) gas at 22 degrees C and 90-95% relative humidity. Approximately a 4.3-4.7 logCFU reduction per strawberry of all examined bacteria was achieved by treatment with 5 mgl(-1) ClO(2) for 10 min. The inactivation kinetics of E. coli O157:H7, L. monocytogenes and S. enterica were determined using first-order kinetic models to establish D-values and z-values. The D-values of E. coli, L. monocytogenes and S. enterica were 2.6+/-0.2, 2.3+/-0.2 and 2.7+/-0.7 min, respectively, at 5 mgl(-1) ClO(2). The z-values of E. coli, L. monocytogenes and S. enterica were 16.8+/-3.5, 15.8+/-3.5 and 23.3+/-3.3 mgl(-1), respectively. Furthermore, treatment with ClO(2) gas significantly (p < or = 0.05) reduced the initial microflora (mesophilic, psychrotrophic bacteria, yeasts and molds) on strawberries. Treatment with ClO(2) gas did not affect the color of strawberries and extended the shelf-life to 16 days compared to 8 days for the untreated control.     

Decontamination of strawberries using batch and continuous chlorine dioxide gas treatments

Efficacy of chlorine dioxide (ClO2) gas in reducing Escherichia coli O157:H7 and Listeria monocytogenes on strawberries was determined using batch and continuous flow ClO2 gas treatment systems. Effects of continuous ClO2 gas treatment on total aerobic plate count, color, and residual ClO2 and chlorite on strawberries were also evaluated. Strawberries were spot inoculated with 7 to 8 log CFU per strawberry of each pathogen (E. coli O157:H7 and L. monocytogenes), stored for 1 day at 4 degrees C, and treated at 22 degrees C and 90 to 95% relative humidity with 0.2 to 4.0 mg/liter ClO2 gas for 15 or 30 min using a batch treatment system or with 0.6, 1.8, and 3.0 mg/liter for 10 min using a continuous treatment system. Surviving microbial populations were determined using a membrane-transfer plating recovery method. Increased ClO2 gas concentrations resulted in increased log reductions of each pathogen for both the batch and continuous systems. A batch treatment of strawberries with 4 mg/liter ClO2 for 30 min and continuous treatment with 3 mg/liter ClO2 for 10 min achieved greater than a 5-log reduction for both E. coli O157:H7 and L. monocytogenes. After continuous exposure to 3.0 mg/liter ClO2 gas for 10 min followed by 1 week of storage at 4 degrees C, no aerobic microorganisms were detected and the color of the strawberry surface did not change significantly (P > 0.05). Residues of ClO2 and chlorite on strawberries after the treatment were 0.19 +/- 0.33 mg ClO2 per kg and 1.17 +/- 2.02 mg Cl2 per kg, respectively, whereas after 1 week of storage no ClO2 residues were detected and residual chlorite levels were down to 0.07 +/- 0.12 mg Cl2 per kg. These results suggest that ClO2 gas treatment is an effective decontamination technique for improving the safety of strawberries while extending shelf life.     

Evaluation of gaseous chlorine dioxide as a sanitizer for killing Salmonella, Escherichia coli O157:H7, Listeria monocytogenes, and yeasts and molds on fresh and fresh-cut produce

Gaseous chlorine dioxide (ClO2) was evaluated for effectiveness in killing Salmonella, Escherichia coli O157:H7, and Listeria monocytogenes on fresh-cut lettuce, cabbage, and carrot and Salmonella, yeasts, and molds on apples, peaches. tomatoes, and onions. Inoculum (100 microl, ca. 6.8 log CFU) containing five serotypes of Salmonella enterica, five strains of E. coli O157:H7, or five strains of L. monocytogenes was deposited on the skin and cut surfaces of fresh-cut vegetables, dried for 30 min at 22 degrees C, held for 20 h at 4 degrees C, and then incubated for 30 min at 22 degrees C before treatment. The skin surfaces of apples, peaches, tomatoes, and onions were inoculated with 100 microl of a cell suspension (ca. 8.0 log CFU) containing five serotypes of Salmonella, and inoculated produce was allowed to dry for 20 to 22 h at 22 degrees C before treatment. Treatment with ClO2 at 4.1 mg/liter significantly (alpha = 0.05) reduced the population of foodborne pathogens on all produce. Reductions resulting from this treatment were 3.13 to 4.42 log CFU/g for fresh-cut cabbage, 5.15 to 5.88 log CFU/g for fresh-cut carrots, 1.53 to 1.58 log CFU/g for fresh-cut lettuce, 4.21 log CFU per apple, 4.33 log CFU per tomato, 1.94 log CFU per onion, and 3.23 log CFU per peach. The highest reductions in yeast and mold populations resulting from the same treatment were 1.68 log CFU per apple and 2.65 log CFU per peach. Populations of yeasts and molds on tomatoes and onions were not significantly reduced by treatment with 4.1 mg/liter ClO2. Substantial reductions in populations of pathogens on apples, tomatoes, and onions but not peaches or fresh-cut cabbage, carrot, and lettuce were achieved by treatment with gaseous ClO2 without markedly adverse effects on sensory qualities.     

Comparative survival of Salmonella typhimurium DT 104, Listeria monocytogenes, and Escherichia coli O157:H7 in preservative-free apple cider and simulated gastric fluid

This study compared the survival of three-strain mixtures (ca. 10(7) CFU ml(-1) each) of Salmonella typhimurium DT104, Listeria monocytogenes, and Escherichia coli O157:H7 in pasteurized and unpasteurized preservative-free apple cider (pH 3.3-3.5) during storage at 4 and 10 degrees C for up to 21 days. S. typhimurium DT104 populations decreased by <4.5 log10 CFU ml(-1) during 14 days storage at 4 and 10 degrees C in pasteurized cider, and by > or =5.5 log10 CFU ml(-1) during 14 days in unpasteurized cider stored at these temperatures. However, after 7 days at 4 degrees C, the S. typhimurium DT104 populations had decreased by only about 2.5 log10 CFU ml(-1) in both pasteurized and unpasteurized cider. Listeria monocytogenes populations decreased below the plating detection limit (10 CFU ml(-1)) within 2 days under all conditions tested. Survival of E. coli O157:H7 was similar to that of S. typhimurium DT104 in pasteurized cider at both 4 and 10 degrees C over the 21-days storage period, but E. coli O157:H7 survived better (ca. 5.0 log10 CFU ml(-1) decrease) than S. typhimurium DT104 (> 7.0 log10 CFU ml(-1) decrease) after 14 days at 4 degrees C in unpasteurized cider. In related experiments, when incubated in simulated gastric fluid (pH 1.5) at 37 degrees C, S. typhimurium DT104 and L. monocytogenes were eliminated (5.5-6.0 log10 CFU ml(-1) decrease) within 5 and 30 min, respectively, whereas E. coli O157:H7 concentrations decreased only 1.60-2.80 log10 CFU ml(-1) within 2 h.     

Efficacy of chlorine dioxide gas as a sanitizer of lettuce leaves

Aqueous solutions of sodium hypochlorite or hypochlorous acid are typically used to sanitize fresh fruits and vegetables. However, pathogenic organisms occasionally survive aqueous sanitization in sufficient numbers to cause disease outbreaks. Chlorine dioxide (ClO2) gas generated by a dry chemical sachet was tested against foodborne pathogens on lettuce leaves. Lettuce leaves were inoculated with cocktail of three strains each of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella Typhimurium and treated with CLO2 gas for 30 min, 1 h, and 3 h in a model gas cabinet at room temperature (22 +/- 2 degrees C). After treatment, surviving cells, including injured cells, were enumerated on appropriate selective agar or using the overlay agar method, respectively. Total ClO2, generated by the gas packs was 4.3, 6.7, and 8.7 mg after 30 min, 1 h, and 3 h of treatment, respectively. Inoculated lettuce leaves exposed to ClO2 gas for 30 min experienced a 3.4-log reduction in E. coli, a 4.3-log reduction in Salmonella Typhimurium, and a 5.0-log reduction in L. monocytogenes when compared with the control. After 1 h. the three pathogens were reduced in number of CFU by 4.4. 5.3, and 5.2 log, respectively. After 3 h, the reductions were 6.9, 5.4, and 5.4 log, respectively. A similar pattern emerged when injured cells were enumerated. The ClO2, gas sachet was effective at killing pathogens on lettuce without deteriorating visual quality. Therefore, this product can be used during storage and transport of lettuce to improve its microbial safety.     

Effects of X-ray treatments on pathogenic bacteria, inherent microflora, color, and firmness on whole cantaloupe

Inactivation of inoculated Escherichia coli O157:H7, Listeria monocytogenes, Salmonella enterica and Shigella flexneri on whole cantaloupes using X-ray at different doses (0.1, 0.5, 1.0, 1.5, and 2.0 kGy) was studied. The effect of X-ray on quality parameters (color and texture) of untreated and treated whole cantaloupes was instrumentally determined. The effect of X-ray on microflora counts (mesophilic counts, psychrotrophic counts and yeast and mold counts) of untreated and treated whole cantaloupes was also determined during storage at 22°C for 20 days. A mixture of three strains of each tested organism was spot inoculated (100 μl), separately, onto the surface (5 cm(2)) of cantaloupe rinds (approximately 8-9 log CFU ml(-1)) separately, air dried (60 min), and then treated with X-ray at 22°C and 55% relative humidity. Surviving bacterial populations on cantaloupe surfaces were evaluated using a nonselective medium (tryptic soy agar) with a selective medium overlay for each bacterium; E. coli O157:H7 (CT-SMAC agar), L. monocytogenes (MOA), and S. enterica and S. flexneri (XLD). More than a 5 log CFU reduction was achieved after treatment with 2.0 kGy X-ray, for all tested pathogens. No significant effect of X-ray treatment on cantaloupe color or firmness was detected. Furthermore, treatment with X-ray significantly reduced the initial inherent microflora on whole cantaloupes and inherent levels were significantly (p<0.05) lower than the control sample throughout storage for 20 days.     

Efficacy of chlorine dioxide gas sachets for enhancing the microbiological quality and safety of blueberries

In response to increasingly stringent microbial specifications being imposed by purchasers of frozen blueberries, chlorine dioxide (ClO2) gas generated by a dry chemical sachet was assessed for inactivation of Listeria monocytogenes, Salmonella spp., and Escherichia coli O157:H7 as well as five yeasts and molds known for blueberry spoilage. Fresh blueberry samples (100 g) were separately inoculated with cocktails of L. monocytogenes, Salmonella, E. coli O157:H7 (three strains each), or yeasts and molds (five strains each) to contain approximately 10(6) CFU/g and exposed to ClO2 (4 mg/liter, 0.16 mg/g) for 12 h in a sealed 20-liter container (99.9% relative humidity) at approximately 22 degrees C. After gassing, 25 g of blueberries was added to 225 ml of neutralizing buffer, pulsified for 1 min, and plated using standard procedures to quantify survivors. This treatment yielded reductions of 3.94, 3.62, 4.25, 3.10, and 3.17 log CFU/g for L. monocytogenes, Salmonella, E. coli O157:H7, yeasts, and molds, respectively. Thereafter, 30 lugs of uninoculated blueberries (approximately 9.1 kg per lug) were stacked on 1.2 by 1.2-m pallets (5 lugs per level x six levels), tarped, and exposed to ClO2 (18 mg/liter, 0.13 mg/g) for 12 h. After gassing, significant (P < 0.05) reductions of 2.33, 1.47, 0.52, 1.63, and 0.48 log CFU/g were seen for mesophilic aerobic bacteria, coliforms, E. coli, yeasts, and molds, respectively, compared with non-gassed controls. No significant differences (P > 0.05) in microbial inactivation were seen between lug levels and, with one exception (mesophilic aerobic bacteria), between the bottom and top surface of individual lugs. Based on these findings, ClO2 sachets may provide a simple, economical, and effective means of enhancing the microbial shelf life and safety of blueberries.     

Effects of recovery, plating, and inoculation methods on quantification of Escherichia coli O157:H7 and Listeria monocytogenes from strawberries

Effects of different recovery and inoculation methods on quantification of Escherichia coli O157:H7 and Listeria monocytogenes from strawberries were studied. Strawberries were spot or dip inoculated with 7 to 8 log CFU per strawberry of each pathogen, air dried for 2 h, and stored for 1, 3, and 7 days at 4 degrees C. The inoculated samples were stomached or washed with phosphate-buffered saline (PBS; pH 7.2) or with modified PBS (pH 8.4). Bacterial levels were determined using a direct selective plating, thin agar layer plating, or membrane-transferring plating (MTP) with tryptic soy agar and sorbital MacConkey agar (E. coli O157:H7) or modified Oxford agar (L. monocytogenes). Under most test conditions, washing with PBS followed by MTP had significantly higher (P < 0.05) recovery for both bacteria compared with other tested methods. Within a 7-day storage period for spot-inoculated strawberries, a stomaching step resulted in an injury of 0.9 to 1.4 log CFU for E. coli O157: H7 and 1.4 to 1.7 log CFU for L. monocytogenes. When a washing step was used instead, this resulted in an injury of only 0.2 to 0.6 log CFU for E. coli O157:H7 and 0.2 to 0.7 log CFU for L. monocytogenes. Both bacteria could survive on strawberry surfaces, but their recovered levels decreased with the increase of storage time at 4 degrees C for both spot and dip inoculation methods. Dip inoculation generally had a lower recovery than spot inoculation. An ideal protocol to recover and enumerate E. coli O157:H7 and L. monocytogenes from strawberries involved shaking and washing samples with 100 ml of PBS for 15 min at 22 degrees C coupled with a MTP enumeration method.     

Identification of a non-pathogenic surrogate organism for chlorine dioxide (ClO2) gas treatment

The identification of non-pathogenic surrogate microorganisms is beneficial for determining and validating the efficacy of antimicrobial treatments in food manufacturing environments. A surrogate organism was identified to aid in the decontamination process of fresh produce when treated with chlorine dioxide (ClO(2)) gas. Thirty-two known strains of pathogenic and non-pathogenic microorganisms and seven unknown microbial isolates from mushroom, tomatoes, and strawberries were evaluated. The primary goal was to find alternative non-pathogenic organisms that had an equal or higher resistance compared to Escherichia coli O157:H7, Salmonella spp., and Listeria monocytogenes. Among the strains tested, MR1 (mushroom isolate), E. coli O157:H7 C7927, E. coli O157:H7 204P, STB2 (strawberry isolate), and vegetative cells of Bacillus cereus 232 in wet inoculum were found to be the most resistant to gaseous ClO(2) treatment at 0.3 mg/l for 1 min and D-values at 0.3 mg/l ClO(2) were 3.53, 1.95, 1.72, 1.68, and 1.57 min, respectively. For identification, the MR1 and STB2 strains were identified using a Ribotyper with the EcoRI restriction enzyme of 16S rDNA sequence. MR1 was identified as Hafnia alvei with a similarity value of 94% using the ribotype pattern and with a 93.6% similarity using an API 20E strip, and with a 99% similarity using 16S rDNA analysis. The Ped-2E9-based cytotoxicity assay was conducted for the MRI strain extracellular toxin and whole cell toxicity and did not show cytotoxicity. Analysis, using multiplex PCR, was performed to verify absence of the eaeA gene. H. alvei is a suitable non-pathogenic surrogate, with higher resistance to ClO(2) gas compared to pathogens studied, that may be useful to establish optimum conditions of ClO(2) gas decontamination systems.     

Effect of chemical sanitizer combined with modified atmosphere packaging on inhibiting Escherichia coli O157:H7 in commercial spinach

Escherichia coli O157:H7 contaminated spinach has recently caused several outbreaks of human illness in the USA and Canada. However, to date, there has been no study demonstrating an effective way to eliminate E. coli O157:H7 in spinach. Therefore, this study was conducted to investigate the effect of chemical sanitizers alone or in combination with packaging methods such as vacuum and modified atmosphere packaging (MAP) on inactivating E. coli O157:H7 in spinach during storage time. Spinach inoculated with E. coli O157:H7 was packaged in four different methods (air, vacuum, N(2) gas, and CO(2) gas packaging) following treatment with water, 100 ppm chlorine dioxide, or 100 ppm sodium hypochlorite for 5 min at room temperature and stored at 7+/-2 degrees C. Treatment with water did not significantly reduce levels of E. coli O157:H7 in spinach. However, treatment with chlorine dioxide and sodium hypochlorite significantly decreased levels of E. coli O157:H7 by 2.6 and 1.1 log(10)CFU/g, respectively. Levels of E. coli O157:H7 in samples packaged in air following treatments grew during storage time, whereas levels were maintained in samples packaged in other packaging methods (vacuum, N(2) gas, and CO(2) gas packaging). Therefore there were significant differences (about 3-4 log) of E. coli O157:H7 populations between samples packed in air and other packaging methods following treatment with chemical sanitizers after 7 days storage. These results suggest that the combination of treatment with chlorine dioxide and packaging methods such as vacuum and MAP may be useful for improving the microbial safety of spinach against E. coli O157:H7 during storage.     

Use of hydrogen peroxide in combination with nisin, sodium lactate and citric acid for reducing transfer of bacterial pathogens from whole melon surfaces to fresh-cut pieces

Hydrogen peroxide (2.5%) alone or hydrogen peroxide (1%) in combination with nisin (25 microg/ml), sodium lactate (1%), and citric acid (0.5%) (HPLNC) were investigated as potential sanitizers for reducing Escherichia coli O157:H7 or Listeria monocytogenes populations on whole cantaloupe and honeydew melons. Whole cantaloupes inoculated with E. coli O157:H7 and L. monocytogenes at 5.27 and 4.07 log10 CFU/cm2, respectively, and whole honeydew melons inoculated with E. coli O157:H7 and L. monocytogenes at 3.45 and 3.05 log10 CFU/cm2, respectively, were stored at 5 degrees C for 7 days. Antimicrobial washing treatments were applied to inoculated whole melons on days 0 or 7 of storage and surviving bacterial populations and the numbers transferred to fresh-cut pieces were determined. At days 0 and 7 treatment with HPLNC significantly (p<0.05) reduced the numbers of both pathogens, by 3 to 4 log CFU/cm2 on both types of whole melon. Treatment with HPLNC was significantly (p<0.05) more effective than treatment with 2.5% hydrogen peroxide. While fresh-cut pieces prepared from stored whole melons were negative for the pathogens by both direct plating and by enrichment, fresh-cut pieces from cantaloupe melons treated with 2.5% hydrogen peroxide were positive for both pathogens and pieces from honeydew melons were positive for E. coli 0157:H7. The native microflora on fresh-cut melons were also substantially reduced by HPLNC treatment of whole melons. The results suggest that HPLNC could be used to decontaminate whole melon surfaces and so improve the microbial safety and quality of fresh-cut melons.     

Combination of high-intensity pulsed electric fields with natural antimicrobials to inactivate pathogenic microorganisms and extend the shelf-life of melon and watermelon juices

The effect of high-intensity pulsed electric field (HIPEF) combined with citric acid (0.5-2.0%, w/v) or cinnamon bark oil (0.05-0.30%, w/v) against populations of Escherichia coli O157:H7, Salmonella Enteritidis and Listeria monocytogenes in melon and watermelon juices were evaluated. Microbiological shelf-life and sensory attributes were also determined. Populations of E. coli O157:H7, S. Enteritidis and L. monocytogenes were reduced by more than 5.0log(10)CFU/ml in HIPEF-processed melon (35kV/cm for 1709 micros at 193Hz and 4 micros pulse duration) and watermelon (35kV/cm for 1682 micros at 193Hz and 4 micros pulse duration) juices containing 2.0% and 1.5% of citric acid, respectively, or 0.2% of cinnamon bark oil. In addition, these treatments were also able to inactivate mesophilic, psychrophilic and, molds and yeasts populations, leading to a shelf-life of more than 91 days in both juices stored at 5 degrees C. Hence, the microbiological quality and safety of these fruit juices by combining HIPEF and citric acid or cinnamon bark oil were ensured. However, the taste and odor in those HIPEF-treated melon and watermelon juices containing antimicrobials were significantly affected. Therefore, further studies are needed to decrease the impact on the sensory attributes by using antimicrobials.     

Reduction of Listeria monocytogenes and Escherichia coli O157:H7 numbers on vacuum-packaged fresh beef treated with nisin or nisin combined with EDTA.

Nisin or nisin combined with EDTA was used to treat fresh beef. Beef cubes (2.5 by 2.5 by 2.5 cm) that were inoculated with approximately 7 log CFU/ml of Listeria monocytogenes Scott A or Escherichia coli O157:H7 505 B were dipped in the following solutions: (i) H2O, (ii) HCl, (iii) nisin, (iv) EDTA, or (v) nisin combined with EDTA, respectively, for 10 min each, with an exception of one set of control beef samples without treatment. Beef samples were then drip-dried for 15 min, vacuum packaged, and stored at 4 degrees C for up to 30 days. The pH on beef after different treatments was not a key factor in preventing bacterial growth. Treatment with nisin or with nisin combined with EDTA reduced the population of L. monocytogenes by 2.01 and 0.99 log CFU/cm2 as compared to the control, respectively, under the conditions of vacuum package and storage at 4 degrees C for up to 30 days. However, the effect of nisin and nisin combined with EDTA against E. coli O157:H7 505 B was marginal at 1.02 log CFU/cm2 and 0.8 log CFU/cm2 reductions, respectively.     

Application of reuterin produced by Lactobacillus reuteri 12002 for meat decontamination and preservation

Lactobacillus reuteri strain 12002 was used for reuterin production in the two-step fermentation process. A batch culture fermentation was used to produce a maximum biomass of L. reuteri. Then cells were harvested, resuspended in a glycerol-water solution, and anaerobically incubated to produce reuterin. The lyophilized supernatants (approximately 4000 activity units (AU) of reuterin per ml) were diluted in distilled water for decontamination and preservation trials. The MIC values of reuterin for Escherichia coli O157:H7 and Listeria monocytogenes were 4 and 8 AU/ml, respectively. In meat decontamination experiments, the surface of cooked pork was inoculated with either L. monocytogenes or E. coli O157:H7 at a level of approximately log10 5 CFU/cm2, incubated for 30 min at 7 degrees C, and decontaminated by exposure to reuterin (500 AU/ml). The bactericidal effect of reuterin was analyzed 15 s and 24 h after exposure at 7 degrees C. After 15 s of exposure to reuterin, viable numbers decreased by 0.45 and 0.3 log10 CFU/cm2 for E. coli O157:H7 and L. monocytogenes, respectively. After 24 h the numbers decreased by 2.7 log10 CFU/cm2 for E. coli O157:H7 and by 0.63 log10 CFU/cm2 for L. monocytogenes. In the same experiment, the combined effect of reuterin and lactic acid was also investigated. Adding lactic acid (5%, vol/vol) to reuterin significantly enhanced (P < or = 0.05) the efficacy of reuterin. No additional effect (P < or = 0.05) was found when ethanol (40%) was added to the mixture of reuterin and lactic acid. To evaluate the preservative effect of reuterin during meat storage, reuterin was added to raw ground pork contaminated with E. coli O157:H7 or L. monocytogenes. Reuterin at a concentration of 100 AU/g resulted in a 5.0-log10 reduction of the viability of E. coli O157:H7 after 1 day of storage at 7 degrees C. Reuterin at a concentration of 250 AU/g reduced the number of the viable cells of L. monocytogenes by log10 3.0 cycles after 1 week of storage at 7 degrees C.     

Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes on plastic kitchen cutting boards by electrolyzed oxidizing water.

One milliliter of culture containing a five-strain mixture of Escherichia coli O157:H7 (approximately 10(10) CFU) was inoculated on a 100-cm2 area marked on unscarred cutting boards. Following inoculation, the boards were air-dried under a laminar flow hood for 1 h, immersed in 2 liters of electrolyzed oxidizing water or sterile deionized water at 23 degrees C or 35 degrees C for 10 or 20 min; 45 degrees C for 5 or 10 min; or 55 degrees C for 5 min. After each temperature-time combination, the surviving population of the pathogen on cutting boards and in soaking water was determined. Soaking of inoculated cutting boards in electrolyzed oxidizing water reduced E. coli O157:H7 populations by > or = 5.0 log CFU/100 cm2 on cutting boards. However, immersion of cutting boards in deionized water decreased the pathogen count only by 1.0 to 1.5 log CFU/100 cm2. Treatment of cutting boards inoculated with Listeria monocytogenes in electrolyzed oxidizing water at selected temperature-time combinations (23 degrees C for 20 min, 35 degrees C for 10 min, and 45 degrees C for 10 min) substantially reduced the populations of L. monocytogenes in comparison to the counts recovered from the boards immersed in deionized water. E. coli O157:H7 and L. monocytogenes were not detected in electrolyzed oxidizing water after soaking treatment, whereas the pathogens survived in the deionized water used for soaking the cutting boards. This study revealed that immersion of kitchen cutting boards in electrolyzed oxidizing water could be used as an effective method for inactivating foodborne pathogens on smooth, plastic cutting boards.     

Surface pasteurization of whole fresh cantaloupes inoculated with Salmonella poona or Escherichia coli

Numerous outbreaks of salmonellosis by Salmonella Poona have been associated with the consumption of cantaloupe. Commercial washing processes for cantaloupe are limited in their ability to inactivate or remove this human pathogen. Our objective was to develop a commercial-scale surface pasteurization process to enhance the microbiological safety of cantaloupe. Populations of indigenous bacteria recovered from cantaloupes that were surface pasteurized at 96, 86, or 76 degrees C for 2 to 3 min were significantly (P < 0.05) lower than those of the controls. Whole cantaloupes, surface inoculated with Salmonella Poona RM 2350 or Escherichia coli ATCC 25922 to a final cell concentration of ca. 5 log CFU/cm2 were stored at 4 degrees C or room temperature (RT = 19+/-1 degrees C) for up to 72 h before processing. Treatments at 76 degrees C for 2 to 3 min at 24 h postinoculation resulted in a reduction in excess of 5 log CFU/cm2 of Salmonella Poona and E. coli populations. Cantaloupes that were surface pasteurized and stored at 4 degrees C for 21 days retained their firmness qualities and had no visible mold growth compared with the controls, which became soft and moldy. These results indicate that surface pasteurization will enhance the microbiological safety of cantaloupes and will extend the shelf life of this commodity as well. Storage of untreated inoculated cantaloupes at RT for 24 to 72 h postinoculation caused a significant (P < 0.05) increase in Salmonella Poona and E. coli populations compared with storage at 4 degrees C. This indicates that cantaloupes should be refrigerated as soon as possible following harvest to suppress the growth of any possible contaminant on the rind.     

Growth and survival of Escherichia coli O157:H7 and Listeria monocytogenes in egg products held at different temperatures

Growth and survival of Escherichia coli O157:H7 and Listeria monocytogenes in steamed eggs and scrambled eggs held at different temperatures (5, 18, 22, 37, 55, and 60 degrees C) were investigated in the present study. Among the holding temperatures tested, both pathogens multiplied best at 37 degrees C followed by 22, 18, and 5 degrees C. In general, E. coli O157:H7 grew better in the egg products than L. monocytogenes did at all the storage temperatures tested except at 5 degrees C. E. coli O157:H7 did not grow in steamed eggs and scrambled eggs held at 5 degrees C. L. monocytogenes showed a slight population increase of approximately 0.6 to 0.9 log CFU/g in these egg products at the end of the 36-h storage period at 5 degrees C. The population of both pathogens detected in the egg products was affected by the initial population, holding temperature, and length of the holding period. It was also noted that L. monocytogenes was more susceptible than E. coli O157:H7 in steamed eggs held at 60 degrees C. After holding at 60 degrees C for 1 h, no detectable viable cells of L. monocytogenes with a population reduction of 5.4 log CFU/g was observed in steamed eggs, whereas a lower population reduction of only approximately 0.5 log CFU/ml was noted for E. coli O157:H7.     

Reduction of bacteria on spinach, lettuce, and surfaces in food service areas using neutral electrolyzed oxidizing water

Food safety issues and increases in food borne illnesses have promulgated the development of new sanitation methods to eliminate pathogenic organisms on foods and surfaces in food service areas. Electrolyzed oxidizing water (EO water) shows promise as an environmentally friendly broad spectrum microbial decontamination agent. EO water is generated by the passage of a dilute salt solution ( approximately 1% NaCl) through an electrochemical cell. This electrolytic process converts chloride ions and water molecules into chlorine oxidants (Cl(2), HOCl/ClO(-)). At a near-neutral pH (pH 6.3-6.5), the predominant chemical species is the highly biocidal hypochlorous acid species (HOCl) with the oxidation reduction potential (ORP) of the solution ranging from 800 to 900mV. The biocidal activity of near-neutral EO water was evaluated at 25 degrees C using pure cultures of Escherichia coli, Salmonella typhimurium, Staphylococcus aureus, Listeria monocytogenes, and Enterococcus faecalis. Treatment of these organisms, in pure culture, with EO water at concentrations of 20, 50, 100, and 120ppm total residual chlorine (TRC) and 10min of contact time resulted in 100% inactivation of all five organisms (reduction of 6.1-6.7log(10)CFU/mL). Spray treatment of surfaces in food service areas with EO water containing 278-310ppm TRC (pH 6.38) resulted in a 79-100% reduction of microbial growth. Dip (10min) treatment of spinach at 100 and 120ppm TRC resulted in a 4.0-5.0log(10)CFU/mL reduction of bacterial counts for all organisms tested. Dipping (10min) of lettuce at 100 and 120ppm TRC reduced bacterial counts of E. coli by 0.24-0.25log(10)CFU/mL and reduced all other organisms by 2.43-3.81log(10)CFU/mL.     

Inactivation of Escherichia coli O157: H7 and Listeria monocytogenes by PR-26, a synthetic antibacterial peptide.

This study reports the antibacterial effect of PR-26, a synthetic peptide derived from the first 26 amino acid sequence of PR-39, an antimicrobial peptide isolated from porcine neutrophils. A three-strain mixture of Escherichia coli O157:H7 or Listeria monocytogenes of approximately 10(8) CFU was inoculated to a final concentration of 10(7) CFU/ml in 1% peptone water (pH 7.0), containing 50 or 75 microg/ml of PR-26, and incubated at 37 degrees C for 0, 6, 12, and 24 h; at 24 degrees C for 0, 12, 24, and 36 h; or at 10 or 4 degrees C for 0, 24, 72, and 120 h. Control samples included 1% peptone water inoculated with each pathogen mixture but containing no PR-26. The surviving population of each pathogen at each sampling time was determined by plating on tryptic soy agar with incubation at 37 degrees C for 24 h. At 37 degrees C, PR-26 decreased E. coli O157:H7 and L. monocytogenes populations by >5.0 log CFU/ml at 12 h, with complete inactivation at 24 h. At 24 degrees C, PR-26 reduced E. coli O157:H7 and L. monocytogenes by approximately 3.5, 4.0, and 4.5 log CFU/ml at the end of 12-, 24-, and 36-h incubations, respectively. At 4 and 10 degrees C, the inhibitory effect of PR-26 on E. coli O157:H7 and L. monocytogenes was significantly lower (P < 0.05) than that at 37 and 24 degrees C: a 2- to 3-log CFU/ml reduction was observed at 120-h incubation. Results indicate that PR-26 could potentially be used as an antimicrobial agent, but applications in appropriate foods need to be validated.