A multiplex RTi-PCR reaction for simultaneous detection of Escherichia coli O157:H7, Salmonella spp. and Staphylococcus aureus on fresh, minimally processed vegetables

In this work, a new multiplex single-tube real-time PCR approach is presented for the detection of Escherichia coli O157:H7, Salmonella spp. and Staphylococcus aureus, three of the more frequent food-borne bacterial pathogens that are usually investigated in a variety of food matrices. The study includes the design and specificity testing, of a new primer and probe specific for Salmonella spp. Reaction conditions were adjusted for the simultaneous amplification and detection of specific fragments in the beta-glucuronidase (uidA, E. coli) and Thermonulease (nuc, Sta. aureus) genes, and in the replication origin sequence (oriC, Salmonella spp.). Melting-curve analysis using a SYBR Green I RTi-PCR approach showed characteristic T(m) values demonstrating the specific and efficient amplification of the three fragments. Subsequently, a TaqMan RTi-PCR approach was settled, using FAM, NED and VIC fluorescently labelled specific probes for an automated detection. It was equally sensitive than uniplex RTi-PCR reactions in Sta. aureus and E. coli O157:H7, using same amounts of purified DNA, and allowed detection of 10 genome equivalents in the presence of 10(2) or 10(4) genome equivalents of the other two pathogens. Finally, it was tested in artificially inoculated fresh, minimally processed vegetables, revealing a sensitivity of 10(3)CFUg(-1) each of these pathogens in direct detection, following DNA extraction with DNeasy Tissue Kit (Qiagen). The multiplex RTi-PCR developed scored the sensitivity recognised for PCR in food and it allows a high-throughput and automation, thus it is promising as a rapid and cost-effective test for the food industry.     

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.     

Simultaneous detection of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella strains by real-time PCR

A protocol enabling simultaneous detection of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella strains was devised and evaluated using artificially contaminated fresh produce. Association of Official Analytical Chemists (AOAC)-approved polymerase chain reaction (PCR) detection methods for three human pathogens were modified to enable simultaneous and real-time detection with high throughput capability. The method includes a melting-curve analysis of PCR products, which serves as confirmatory test. The modified protocol successfully detected all three pathogens when fresh produce was washed with artificially contaminated water containing E. coli O157:H7 and S. typhimurium down to the predicted level of 1 to 10 cells/ml and L. monocytogenes at 1000 cells/ml. The ability to monitor several pathogens simultaneously will save time and increase our ability to assure food safety.     

Survival and growth of Listeria monocytogenes and enterohemorrhagic Escherichia coli O157:H7 in minimally processed artichokes

The ability of Listeria monocytogenes and Escherichia coli O157:H7 inoculated by immersion (at 4.6 and 5.5 log CFU/ g, respectively) to survive on artichokes during various stages of preparation was determined. Peeling, cutting, and disinfecting operations (immersion in 50 ppm of a free chlorine solution at 4 degrees C for 5 min) reduced populations of L. monocytogenes and E. coli O157:H7 by only 1.6 and 0.8 log units, respectively. An organic acid rinse (0.02% citric acid and 0.2% ascorbic acid) was more effective than a tap water rinse in removing these pathogens. Given the possibility of both pathogens being present on artichokes at the packaging stage, their behavior during the storage of minimally processed artichokes was investigated. For this purpose, batches of artichokes inoculated with L. monocytogenes or E. coli O157:H7 (at 5.5 and 5.2 log CFU/g, respectively) were packaged in P-Plus film bags and stored at 4 degrees C for 16 days. During this period, the equilibrium atmosphere composition and natural background microflora (mesophiles, psychrotrophs, anaerobes, and fecal coliforms) were also analyzed. For the two studied pathogens, the inoculum did not have any effect on the final atmospheric composition (10% O2, 13% CO2) or on the survival of the natural background microflora of the artichokes. L. monocytogenes was able to survive during the entire storage period in the inoculated batches, while the E. coli O157:H7 level increased by 1.5 log units in the inoculated batch during the storage period. The modified atmosphere was unable to control the behavior of either pathogen.     

三重荧光PCR检测沙门氏菌、金黄色葡萄球菌和大肠埃希氏菌O157:H7

目的 建立一种检验沙门氏菌、金黄色葡萄球菌、大肠埃希氏菌O157:H7的TaqMan探针三重荧光PCR方法.方法 针对沙门氏菌属特异性invA基因、金黄色葡萄球菌rpoB基因、大肠埃希氏菌O157:H7的rfbE基因设计引物与探针,建立三重荧光PCR体系,对引物与探针浓度及退火温度优化,并进行特异性和敏感性研究.结果 ...     

Multiplex PCR for simultaneous detection of Salmonella spp., Listeria monocytogenes, and Escherichia coli O157:H7 in meat samples

A multiplex PCR method was developed for simultaneous detection of Salmonella spp., Listeria monocytogenes, and Escherichia coli O157:H7 in meat samples. DNA detection sensitivity for this method was 10(3) CFU/ml for each pathogen. When this protocol was used for the detection of each of the above pathogenic bacteria in spiked pork samples, 1 cell per 25 g of inoculated sample could be detected within 30 h. In the samples of naturally contaminated meat, Salmonella spp., L. monocytogenes, and E. coli O157:H7 were detected over the same time period. Excellent agreement was obtained for the results of multiplex PCR and the conventional culture method, which suggests that the multiplex PCR is a reliable and useful method for rapid screening of meat products for Salmonella spp., L. monocytogenes, and E. coli O157:H7 contamination.     

Evaluation of a polymerase chain reaction-based system for detection of Salmonella enteritidis, Escherichia coli O157:H7, Listeria spp., and Listeria monocytogenes on fresh fruits and vegetables

A polymerase chain reaction (PCR)-based detection system, BAX, was evaluated for its sensitivity in detecting Salmonella Enteritidis, Escherichia coli O157:H7, Listeria sp., and Listeria monocytogenes on fresh produce. Fifteen different types of produce (alfalfa sprouts, green peppers, parsley, white cabbage, radishes, onions, carrots, mushrooms, leaf lettuce, tomatoes, strawberries, cantaloupe, mango, apples, and oranges) were inoculated, in separate studies, with Salmonella Enteritidis, E. coli O157:H7, and L. monocytogenes down to the predicted level of 1 CFU per 25-g sample. Detection by BAX was compared to recovery of the inoculated bacteria by culture methods according to the Food and Drug Administration's (FDA) Bacteriological Analytical Manual (BAM). BAX was essentially as sensitive as the culture-based method in detecting Salmonella Enteritidis and L. monocytogenes and more sensitive than the culture-based method for the detection of E. coli O157:H7 on green pepper, carrot, radish, and sprout samples. Detection of the pathogenic bacteria in samples spiked with a predicted number of less than 10 CFU was possible for most produce samples, but both methods failed to detect L. monocytogenes on carrot samples and one of two mushroom and onion samples spiked with less than 100 CFU. Both BAX and the culture method were also unable to consistently recover low numbers of E. coli O157:H7 from alfalfa sprouts. The PCR method allowed detection of Salmonella Enteritidis, E. coli O157:H7, and L. monocytogenes at least 2 days earlier than the conventional culture methods.     

Inactivation of Salmonella Typhimurium,Escherichia coli O157:H7, Staphylococcus aureus,and Listeria monocytogenes in cardamom using 150 KeV low-energy X-ray

This study aimed to investigate the inactivation effect of 150 KeV low-energy X-ray on Salmonella Typhimurium, Escherichia coli O157:H7, Staphylococcus aureus, and Listeria monocytogenes that were inoculated in dry cardamom. The D₁₀ value for E. coli O157:H7 was 71.43 Gy and the t_R values for S. Typhimurium, L. monocytogenes, and S. aureus were 53.57, 87.74, and 114.64 Gy, respectively. The irradiation did not significantly affect the amount of mono-unsaturated fatty acids (MUFAs) in cardamom; however, the content of poly-unsaturated fatty acids (PUFAs) decreased by approximate 20%. No 2-alkylcyclobutanones (2-ACBs), dimethyl disulfide and 3-methyl-thiophene were detected in the irradiated dry cardamom. These findings indicated that 150 KeV low-energy X-ray could be applied to effectively inactivate pathogens in dry cardamom.Industrial relevanceIt was shown that low-energy X-ray irradiation up to 350 Gy did not generate 2-ACBs, dimethyl disulfide and 3-methyl-thiophene in dry cardamom, which are among the major concerns with the application of food irradiation. The outcomes of this research highlight the potential of low-energy X-ray for the preservation of low moisture foods.     

Survival of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella in juice concentrates

The survival of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella was studied in apple, orange, pineapple, and white grape juice concentrates and banana puree. Pouches of juice concentrate or puree were inoculated with pathogens at a level > or = 10(3) CFU/g and stored at -23 degrees C (-10 degrees F). Pathogen survival was monitored at 6 and 24 h, once a week for four consecutive weeks, and biweekly thereafter until 12 weeks. When pathogens were not detectable by direct plating, samples were enriched in universal preenrichment broth for 72 h and plated on selective media. Results showed that E. coli O157:H7, L. monocytogenes, and Salmonella were recoverable from all five concentrates through 12 weeks of storage at -23 degrees C.     

SSEL,a selective enrichment broth for simultaneous growth of Salmonella enterica,Staphylococcus aureus,Escherichia coli O157: H7, and Listeria monocytogenes

Salmonella enterica, Staphylococcus aureus, Escherichia coli O157: H7, and Listeria monocytogenes may contaminate similar types of food and cause foodborne disease. The objective of this study was to develop a selective enrichment broth for simultaneous enrichment of Salmonella enterica, Staphylococcus aureus, Escherichia coli O157: H7, and Listeria monocytogenes (SSEL) using nalidixic acid, acriflavine, lithium chloride, and sodium cholate as selective agents. Developed SSEL broth not only enriched the target pathogens to 5 log10 CFU/ml after 18 hr incubation at 37°C with 10–100 CFU/mL of inoculation concentration, but also could successfully support the simultaneous enrichment of target pathogens with similar growth rates and inhibit the growth of most nontarget bacteria effectively. The enrichment effect of SSEL was confirmed by artificial contamination test coupled with multiplex PCR. In summary, SSEL has been shown to be a promising multiplex selective enrichment broth for the detection of the four pathogens on a single-assay platform.     

A novel multiplex PCR assay for rapid and simultaneous detection of five pathogenic bacteria: Escherichia coli O157:H7, Salmonella, Staphylococcus aureus, Listeria monocytogenes, and Vibrio parahaemolyticus

Rapid and sensitive detection techniques for foodborne pathogens are important to the food industry. However, traditional detection methods rely on bacterial culture in combination with biochemical tests, a process that typically takes 4 to 7 days to complete. Thus, this study was conducted to address the issue of time lag inherent in traditional methods by developing a novel PCR assay for each of five foodborne pathogenic bacteria. This new system consists of a simultaneous screening method using multiplex PCR in a single reaction tube for the rapid and sensitive detection of each of the five bacteria. Specific primers for multiplex PCR amplification of the Shiga-like toxin (verotoxin type II), femA (cytoplasmic protein), toxR (transmembrane DNA binding protein), iap (invasive associative protein), and invA (invasion protein A) genes were designed to allow simultaneous detection of Escherichia coli O157:H7, Staphylococcus aureus, Vibrio parahaemolyticus, Listeria monocytogenes, and Salmonella, respectively. To confirm the specificity of each primer pair for the respective target gene, three types of experiments were carried out using boiled cell lysates and their DNAs. In the multiplex PCR with mixed DNA samples, specific bands for corresponding genes were simultaneously detected from a single reaction. The detection of all five foodborne pathogenic bacteria could be completed in less than 24 h with this novel PCR method.     

Destruction of Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Staphylococcus aureus achieved during manufacture of whole-muscle beef Jerkyin home-style dehydrators

Adequate lethality in jerky manufacture destroys appropriate levels of Escherichia coli O157:H7, Salmonella, Listeria monocytogenes, and Staphylococcus aureus. Our goal was to evaluate the lethality of four home-style dehydrator processes against these pathogens. Whole-muscle beef strips were inoculated with L. monocytogenes (five strains), S. aureus (five strains), or a mixed inoculum of E. coli O157:H7 (five strains) and Salmonella (eight strains). After allowing for attachment, strips were marinated in Colorado-, Original-, or Teriyaki-seasoned marinade for 22 to 24 h and dried in three home-style dehydrators (Garden Master, Excalibur, and Jerky Xpress) at 57.2 to 68.3°C. Samples were taken postmarination; after 4, 6, and 8 h of drying; and after drying, followed by heating for 10 min in a 135°C oven. Surviving inocula were enumerated. With a criterion of ≥ 5.0-log CFU/cm2 reduction as the standard for adequate process lethality, none of the samples achieved the target lethality for any pathogen after 4 h of drying, even though all samples appeared "done" (water activity of less than 0.85). A postdehydration oven-heating step increased the proportion of samples meeting the target lethality after 4 h of drying to 71.9, 88.9, 55.6, and 77.8% for L. monocytogenes-, S. aureus-, E. coli O157:H7-, and Salmonella-inoculated samples, respectively, and after an 8-h drying to 90.6, 94.4, 83.3, and 91.7% of samples, respectively. Significantly greater lethality was seen with higher dehydrator temperature and significantly lower with Teriyaki-marinated samples. Heating jerky dried in a home-style dehydrator for 10 min in a 135°C oven would be an effective way to help ensure safety of this product.     

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 activity of pediocin-producing Lactococcus lactis on Listeria monocytogenes,Staphylococcus aureus and Escherichia coli O157:H7 in cheese

The antimicrobial activity of two pediocin-producing transformants obtained from wild strains of Lactococcus lactis on the survival of Listeria monocytogenes, Staphylococcus aureus and Escherichia coli O157:H7 during cheese ripening was investigated. Cheeses were manufactured from milk inoculated with the three pathogens, each at approximately 6 log cfu mL⁻¹. Pediococcus acidilactici 347 (Ped⁺), Lc. lactis ESI 153, Lc. lactis ESI 515 (Nis⁺) and their respective pediocin-producing transformants Lc. lactis CL1 (Ped⁺) and Lc. lactis CL2 (Nis⁺, Ped⁺) were added at 1% as adjuncts to the starter culture. After 30 d, L. monocytogenes, S. aureus and E. coli O157:H7 counts were 5.30, 5.16 and 4.14 log cfu g⁻¹ in control cheese made without adjunct culture. On day 30, pediocin-producing derivatives Lc. lactis CL1 and Lc. lactis CL2 lowered L. monocytogenes counts by 2.97 and 1.64 log units, S. aureus by 0.98 and 0.40 log units, and E. coli O157:H7 by 0.84 and 1.69 log units with respect to control cheese. All cheeses made with nisin-producing LAB exhibited bacteriocin activity throughout ripening. Pediocin activity was only detected throughout the whole ripening period in cheese with Lc. lactis CL1. Because of the antimicrobial activity of pediocin PA-1, its production in situ by strains of LAB growing efficiently in milk would extend the application of this bacteriocin in cheese manufacture.     

Incidence of Salmonella, Listeria monocytogenes, Escherichia coli O157:H7, and Staphylococcal enterotoxin in two types of Mexican fresh cheeses

Handcrafted fresh cheeses are popular among consumers in Mexico. However, unsafe raw materials and inadequate food safety practices during cheese manufacture and preservation make them a potential public health risk. The incidence of Salmonella, Listeria, Escherichia coli O157:H7, and staphylococcal enterotoxin was analyzed in two types of fresh cheese (panela and adobera) commonly marketed in Mexico. A total of 200 samples, 100 panela and 100 adobera, were acquired from 100 wholesale milk product distributors who supply small retailers in the Guadalajara metropolitan area, Jalisco State, Mexico. Pathogens were identified using culture and immunoassay (miniVidas) methods. The presence of staphylococcal enterotoxin was determined by an immunoassay method. Of the 200 analyzed samples, 92 were positive for at least one of the pathogens. The incidence in the panela samples was 56%: 34% Salmonella, 16% E. coli O157:H7, and 6% L. monocytogenes. In the adobera samples, incidence was 36%: 20% Salmonella, 4% E. coli O157:H7, and 12% L. monocytogenes. Staphylococcal enterotoxin was not detected in any of the 200 samples. Choice of technique had no effect on detection of pathogen incidence, although the immunoassay method identified more Salmonella serotypes than the culture method. Handcrafted panela and adobera fresh cheeses in Mexico frequently contain pathogenic bacteria and therefore pose a public health risk.     

Thermal inactivation of Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes in breaded pork patties

ABSTRACT:  Decimal reduction times ( D -values) and thermal resistance constants ( z -values) for 3 foodborne pathogenic bacteria in formulated ready-to-eat breaded pork patties were determined with thermal inactivation studies. Meat samples, inoculated with Escherichia coli O157:H7, Salmonella , and Listeria monocytogenes cultures or uninoculated controls, were packaged in sterile bags, immersed in circulated water bath, and held at 55, 57.5, 60, 62.5, 65, 67.5, and 70 °C for different durations of time. The D - and z -values were determined by using a linear regression model. Average calculated D -values for E. coli O157:H7, Salmonella , and L . monocytogenes at a temperature range of 55 to 70 °C were 32.11 to 0.08 min, 69.48 to 0.29 min, and 150.46 to 0.43 min, respectively. Calculated z -values for E. coli O157:H7, Salmonella , and L. monocytogenes were 5.4, 6.2, and 5.9 °C, respectively. The results of this study will be useful to food processors to validate thermal lethality of the studied foodborne pathogens in ready-to-eat breaded pork patties.     

Thermal resistance of Listeria monocytogenes, Salmonella Heidelberg, and Escherichia coli O157:H7 at elevated temperatures

A continuous-flow apparatus was developed to measure thermal resistance (D- and z-values) of microorganisms at temperatures above 65 degrees C. This apparatus was designed to test whether vegetative microorganisms exhibited unusually high thermal resistance that prevented them from being completely eliminated at temperatures applicable to vacuum-steam-vacuum processes (116 to 157 degrees C). The apparatus was composed of a high-pressure liquid chromatography pump, a heating unit, and a cooling unit. It was designed to measure small D-values (<1 s). Three randomly selected organisms, Listeria monocytogenes, Salmonella Heidelberg, and Escherichia coli O157:H7 suspended in deionized water were tested in the continuous-flow apparatus at temperatures ranging from 60 to 80 degrees C. Studies showed that the D-values of these organisms ranged from 0.05 to 20 s. Heating at 80 degrees C was found to be basically the physical limit of the system. Experimental results showed that L. monocytogenes, Salmonella Heidelberg, and E. coli O157:H7 did not exhibit unusual heat resistance. The conditions used in the vacuum-steam-vacuum processes should have completely inactivated organisms such as L. monocytogenes, Salmonella Heidelberg, and E. coli O157:H7 if present on food surfaces. The complete destruction of bacteria during vacuum-steam-vacuum processes might not occur because the surface temperatures never reached those of the steam temperatures and because bacteria might be hidden beneath the surface and was thus never exposed to the destructive effects of the steam.     

Validation of apple cider pasteurization treatments against Escherichia coli O157:H7, Salmonella, and Listeria monocytogenes.

Time and temperature pasteurization conditions common in the Wisconsin cider industry were validated using a six-strain cocktail of Escherichia coli O157:H7 and acid-adapted E. coli O157:H7 in pH- and degrees Brix-adjusted apple cider. Strains employed were linked to outbreaks (ATCC 43894 and 43895, C7927, and USDA-FSIS-380-94) or strains engineered to contain the gene for green fluorescent protein (pGFP ATCC 43894 and pGFP ATCC 43889) for differential enumeration. Survival of Salmonella spp. (CDC 0778. CDC F2833, and CDC H0662) and Listeria monocytogenes (H0222, F8027, and F8369) was also evaluated. Inoculated cider of pH 3.3 or 4.1 and 11 or 14 degrees Brix was heated under conditions ranging from 60 degrees C for 14 s to 71.1 degrees C for 14 s. A 5-log reduction of nonadapted and acid-adapted E. coli O157:H7 was obtained at 68.1 degrees C for 14 s. Lower temperatures, or less time at 68.1 degrees C, did not ensure a 5-log reduction in E. coli O157:H7. A 5-log reduction was obtained at 65.6 degrees C for 14 s for Salmonella spp. L. monocytogenes survived 68.1 degrees C for 14 s, but survivors died in cider within 24 h at 4 degrees C. Laboratory results were validated with a surrogate E coli using a bench-top plate heat-exchange pasteurizer. Results were further validated using fresh unpasteurized commercial ciders. Consumer acceptance of cider pasteurized at 68.1 degrees C for 14 s (Wisconsin recommendations) and at 71.1 degrees C for 6 s (New York recommendations) was not significantly different. Hence, we conclude that 68.1 degrees C for 14 s is a validated treatment for ensuring adequate destruction of E. coli O157:H7, Salmonella spp., and L. monocytogenes in apple cider.     

Use of organic acids to inactivate Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on organic fresh apples and lettuce

Abstract: This study was undertaken to investigate the antimicrobial effect of organic acids against Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on whole red organic apples and lettuce. Several studies have been conducted to evaluate organic acids as sanitizers. However, no studies have compared antimicrobial effects of various organic acids on organic fresh produce, including evaluation of color changes of produce. Apples and lettuce were inoculated with a cocktail of 3 strains each of 3 foodborne pathogens provided above and treated with 1% and 2% organic acids (propionic, acetic, lactic, malic, and citric acid) for 0, 0.5, 1, 5, and 10 min. With increasing treatment time and acid concentration, organic acid treatments showed significant reduction compared to the control treatment (distilled water), and differences in antimicrobial effects between organic acids were observed. After 10 min of treatment with 1% and 2% organic acids in apples, propionic (0.92 to 2.75 log reduction), acetic (0.52 to 2.78 log reduction), lactic (1.69 to >3.42 log reduction), malic (1.48 to >3.42 log reduction), and citric acid (1.52 to >3.42 log reduction) exhibited significant (P < 0.05) antibacterial effects against 3 foodborne pathogens compared to the control treatment. In lettuce, propionic (0.93 to 1.52 log reduction), acetic (1.13 to 1.74 log reduction), lactic (1.87 to 2.54 log reduction), malic (2.32 to 2.98 log reduction), and citric acid (1.85 to 2.86 log reduction) showed significant (P < 0.05) effects compared to the control treatment. Changes in sample color subjected to organic acids treatment were not significant during storage. Practical Application: It is suggested that organic acids have a potential as sanitizers for organic fresh produce. These data may help the organic produce industry provide safe fresh produce for consumers.     

Optimization of rapid detection of Escherichia coli O157:H7 and Listeria monocytogenes by PCR and application to field test

For rapid detection of Escherichia coli O157:H7 and Listeria monocytogenes, simple methods for sample preparation and PCR were established and applied to a field test. To improve specificity, primer sets LP43-LP44 and C(+)-D(-) were selected for E. coli O157:H7 and L. monocytogenes, respectively. Through centrifugation and partial heat treatment after enrichment, E. coli O157:H7 and L. monocytogenes were detected at 1 initial CFU without genomic DNA extraction in the culture and with artificially inoculated food samples including milk, chicken, ham, and pork. Based on the optimized PCR method, a feasibility test was carried out using randomly collected field samples. To remove false positives and false negatives, a PCR method using several primer sets, including the optimized primer set, and a standard culture method were used. With the PCR detection and standard culture methods, two pork samples were positive for L. monocytogenes after enrichment, indications that the PCR assay could be effectively used for rapid, sensitive, and species-specific detection of foodborne pathogens.