Individual and combined application of dry heat with high hydrostatic pressure to inactivate Salmonella and Escherichia coli O157:H7 on alfalfa seeds

Alfalfa sprouts are recurrently implicated in outbreaks of food-borne illnesses as a result of contamination with Salmonella or Escherichia coli O157:H7. In the majority of these outbreaks, the seeds themselves have been shown to be the most likely source of contamination. The aims of this study were to comparatively assess the efficacy of dry heat treatments alone or in conjunction with high hydrostatic pressure (HHP) to eliminate a ∼5 log CFU/g load of Salmonella and E. coli O157:H7 on alfalfa seeds. Dry heat treatments at mild temperatures of 55 and 60 °C achieved ≤1.6 and 2.2 log CFU/g reduction in the population of Salmonella spp. after a 10-d treatment, respectively. However, subjecting alfalfa seeds to more aggressive temperatures of 65 °C for 10 days or 70 °C for 24 h eliminated a ∼5 log population of Salmonella and E. coli O157:H7. We subsequently showed that the sequential application of dry heating followed by HHP could substantially reduce the dry heating exposure time while achieving equivalent decontamination results. Dry heating at 55, 60, 65 and 70 °C for 96, 24, 12 and 6 h, respectively followed by a pressure treatment of 600 MPa for 2 min at 35 °C were able to eliminate a ∼5 log CFU/g initial population of both pathogens. Finally, we evaluated the impact of selected treatments on the seed germination percentages and yield ratios and showed that dry heating at 65 °C for 10 days did not bring about any considerable decrease in the germination percentage. However, the sprout yield of treated alfalfa seeds was reduced by 21%. Dry heating at 60 and 65 °C for 24 and 12 h respectively followed by the pressure treatment of 600 MPa for 2 min at 35 °C did not significantly (P > 0.05) affect the germination percentage of alfalfa seeds although a reduction in the sprouting yield was observed.     

Fate of Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella on fresh-cut celery

Illnesses from Escherichia coli O157:H7, Listeria monocytogenes, and Salmonella have been associated with the consumption of numerous produce items. Little is known about the effect of consumer handling practices on the fate of these pathogens on celery. The objective of this study was to determine pathogen behavior at different temperatures under different storage conditions. Commercial fresh-cut celery was inoculated at ca. 3 log CFU/g onto either freshly cut or outer uncut surfaces and stored in either sealed polyethylene bags or closed containers. Samples were enumerated following storage for 0, 1, 3, 5, and 7 days when held at 4 °C or 12 °C, and after 0, 8, and 17 h, and 1, and 2 days when held at 22 °C. At 4 °C, all populations declined by 0.5–1.0 log CFU/g over 7 days. At 12 °C, E. coli O157:H7 and Salmonella populations did not change, while L. monocytogenes populations increased by ca. 0.5 log CFU/g over 7 days. At 22 °C, E. coli O157:H7, Salmonella, and L. monocytogenes populations increased by ca. 1, 2, or 0.3 log CFU/g, respectively, with the majority of growth occurring during the first 17 h. On occasion, populations on cut surfaces were significantly higher than those on uncut surfaces. Results indicate that populations are reduced under refrigeration, but survive and may grow at elevated temperatures.     

Antimicrobial activity of lactic acid and copper on growth of Salmonella and Escherichia coli O157:H7 in laboratory medium and carrot juice

Outbreaks of food-borne pathogens, such as Escherichia coli O157:H7 and Salmonella, continue to draw public attention to food safety. Several reports have demonstrated the efficacy of using natural ingredients to control the growth of food-borne pathogens. The objective of this study was to investigate antimicrobial effects of lactic acid and copper, alone and in combination, on the survival and growth of Salmonella spp. and E. coli O157:H7 in laboratory medium and carrot juice. Survival and growth of 38 Salmonella spp. and six E. coli O157:H7 strains were compared when grown in brain heart infusion (BHI) broth and carrot juice under conditions including either lactic acid (0.2%) alone, copper sulfate (50 ppm) alone or the combination of the two. The growth inhibition was negligible when copper sulfate was added to BHI broth and carrot juice. Lactic acid (0.2%) retarded the growth of bacterial strains. However, the growth of bacterial strains was significantly inhibited when both lactic acid and copper were in BHI broth and carrot juice within the time frame of this study. These findings indicated that lactic acid, in combination with copper sulfate, could be used to inhibit the growth of pathogens. Natural ingredients, such as lactic acid and low dose of copper ions, can be used to improve the safety of food products.     

Salmonella, Escherichia coli O157:H7 and E. coli biotype 1 in a pilot survey of imported and New Zealand pig meats

A pilot survey for the pathogens Salmonella and Escherichia coli O157:H7, and E. coli biotype 1 was conducted on 100 New Zealand-produced (domestic) pig carcasses and 110 imported pig meat samples over an 8-month period to assess the likelihood of introduction of novel pathogen strains into New Zealand (NZ), and as a guide for development of a domestic pork National Microbiological Database programme. Salmonella was not isolated from domestic pig carcasses or from pig meat imported from Canada and the USA. The prevalence of Salmonella in imported pig meat was 3.6% (95% CI 1.0–9.0) with positive samples detected from Australian pig meat. The prevalence of E. coli O157:H7 on domestic pig carcasses was 1% (95% CI 0.03–5.4) while the overall prevalence of E. coli O157:H7 in imported pig meat was 1.8% (95% CI 0.2–6.4), detected mainly from Australian but not from Canadian or US pork. All except three samples have an E. coli biotype 1 count of <100 CFU cm⁻² or g⁻¹, indicating good hygiene quality of domestic and imported pig meat. The results demonstrated that importation of uncooked pig meat is a potential route for the introduction of new clones of Salmonella and E. coli O157:H7 into New Zealand.     

Inactivation of Escherichia coli O157:H7 on stainless steel upon exposure to Paenibacillus polymyxa biofilms

We investigated the potential use of biofilm formed by a competitive-exclusion (CE) microorganism to inactivate Escherichia coli O157:H7 on a stainless steel surface. Five microorganisms showing inhibitory activities against E. coli O157:H7 were isolated from vegetable seeds and sprouts. The microorganism with the greatest antimicrobial activity was identified as Paenibacillus polymyxa (strain T5). In tryptic soy broth (TSB), strain T5 reached a higher population at 25 °C than at 12 or 37 °C without losing inhibitory activity against E. coli O157:H7. When P. polymyxa (6 log CFU/mL) was co-cultured with E. coli O157:H7 (2, 3, 4, or 5 log CFU/mL) in TSB at 25 °C, the number of E. coli O157:H7 decreased significantly within 24 h. P. polymyxa formed a biofilm on stainless steel coupons (SSCs) in TSB at 25 °C within 24 h, and cells in biofilms, compared to attached cells without biofilm formation, showed significantly increased resistance to a dry environment (43% relative humidity [RH]). With the exception of an inoculum of 4 log CFU/coupon at 100% RH, upon exposure to biofilm formed by P. polymyxa on SSCs, populations of E. coli O157:H7 (2, 4, or 6 log CFU/coupon) were significantly reduced within 48 h. Most notably, when E. coli O157:H7 at 2 log CFU/coupon was applied to SSCs on which P. polymyxa biofilm had formed, it was inactivated within 1 h, regardless of RH. These results will be useful when developing strategies using biofilms produced by competitive exclusion microorganisms to inactivate foodborne pathogens in food processing environments.     

Application of high hydrostatic pressure to decontaminate green onions from Salmonella and Escherichia coli O157:H7

Consumption of fecally contaminated green onions has been implicated in several major outbreaks of foodborne illness. The objectives of this study were to investigate the survival and growth of Salmonella and Escherichia coli O157:H7 in green onions during storage and to assess the application of high hydrostatic pressure (HHP) to decontaminate green onions from both pathogens. Bacterial strains resistant to nalidixic acid and streptomycin were used to inoculate green onions at low (∼1 log cfu/g) and high (∼2 log cfu/g) inoculum levels which were then kept at 4 or 22 °C for up to 14 days. Both pathogens grew to an average of 5-6 log cfu/g during storage at 22 °C and the bacterial populations were fairly stable during storage at 4 °C. High-pressure processing of inoculated green onions in the un-wetted, wetted (briefly dipped in water) or soaked (immersed in water for 30 min) conditions at 250-500 MPa for 2 min at 20 °C reduced the population of Salmonella and E. coli O157:H7 by 0.6 to >5 log cfu/g, depending on the pressure level and sample wetness state. The extent of pressure inactivation increased in the order of soaked > wetted > un-wetted state. The pressure sensitivity of the pathogens was also higher at elevated treatment temperatures. Overall, after pressure treatment at 400-450 MPa (soaked) or 450-500 MPa (wetted) for a retention time of 2 min at 20-40 °C, wild-type and antibiotic-resistant mutant strains of Salmonella and E. coli O157:H7 inoculated on green onions were undetectable immediately after treatment and throughout the 15-day storage at 4 °C. The pressure treatments also had minimal adverse impact on most sensorial characteristics as well as on the instrumental color of chopped green onions. This study highlights the promising applications of HHP to minimally process green onions in order to alleviate the risks of Salmonella and E. coli O157:H7 infections associated with the consumption of this commodity.     

Survey of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 in raw ingredients and ready-to-eat products by commercial real-time PCR kits

Real-time PCR (RTiPCR) assays including enrichment stage were evaluated for the rapid detection of Listeria monocytogenes, Salmonella spp. and Escherichia coli O157:H7 in raw ingredients and ready-to-eat products using molecular beacon probes available as commercial kits (WARNEX Genevision, Canada & AES Chemunex detection system, France). The accuracy of the assays was evaluated analyzing 1032 naturally contaminated food samples in combination to the conventional cultural methods. Presence/absence testing of the above pathogens was performed in 25 g samples of each product. In case of L. monocytogenes of 39 positive RTiPCR samples, 37 were confirmed by the cultural method (based on McNemar's test the difference between the two methods is insignificant). The highest incidence of L. monocytogenes in food products was found in desserts and the second highest in frozen pastries. None of the samples were cultural positive but negative in the RTiPCR test. One among the 343 investigated samples was positive for Salmonella spp. by RTiPCR and the cultural method. Out of 333 samples analyzed for E. coli O157:H7 no positive sample was detected. RTiPCR-based methods proved to be powerful tools for fast, sensitive and accurate pathogen detection in raw food ingredients and ready-to-eat products.     

Survival of Escherichia coli O157:H7 in channel catfish pond and holding tank water

Survival of Escherichia coli O157:H7 in channel catfish (Ictalurus punctatus), pond and holding tank water was investigated. Water from three channel catfish ponds was inoculated with ampicillin/nalidixic acid-resistant E. coli O157:H7 transformed with a plasmid encoding for green fluorescent protein at 10⁵, 10⁶, and 10⁷ CFU/ml. Samples were taken from surface, internal organs, and skin scrape of fish and pond water for E. coli O157:H7 enumeration on brain heart infusion (BHI) agar containing ampicillin and nalidixic acid. To determine the survival of E. coli O157:H7 in catfish holding tank water from two farmers markets, the water was inoculated with 10⁷E. coli O157:H7 CFU/ml. E. coli O157:H7 were detected by direct plating for 33 and 69 d in pond and holding tank water, respectively. A rapid decrease of the pathogen was observed in the first 2 weeks to reach 2 log CFU/ml. When E. coli O157:H7 was not recovered by direct plating, the pathogen was isolated by enrichment in TSB for approximately another 30 d from pond and holding tank water. The populations of E. coli O157:H7 found in the internal organs and skin scrape were 5.5 log and 2.5 log CFU/ml, respectively. E. coli O157:H7 from internal organs and water were recovered for at least 12 d. Results suggest that E. coli O157:H7 can survive in channel catfish pond and holding tank water and channel catfish may become a potential carrier of the pathogen.     

Prevalence and antimicrobial susceptibility of Escherichia coli O157:H7 on beef cattle slaughtered in Amman abattoir

Cattle are the main asymptomatic reservoir of Escherichia coli O157:H7 which can cause illness to human. The objectives of the study were to measure the prevalence of E. coli O157:H7 on cattle slaughtered in Amman abattoir, detect virulence factors in the isolates, determine antibacterial resistance of the isolates, and know how the isolates are different or similar when compared to characterized isolates from developed countries.     

Enhancing the thermal destruction of Escherichia coli O157:H7 in ground beef patties by trans-cinnamaldehyde

The effect of trans-cinnamaldehyde (TC) on the inactivation of Escherichia coli O157:H7 in undercooked ground beef patties was investigated. A five-strain mixture of E. coli O157:H7 was inoculated into ground beef (7.0 log CFU/g), followed by addition of TC (0, 0.15, and 0.3%). The meat was formed into patties and stored at 4 °C for 5 days or at −18 °C for 7 days. The patties were cooked to an internal temperature of 60 or 65 °C, and E. coli O157:H7 was enumerated. The numbers of E. coli O157:H7 did not decline during storage of patties. However, cooking of patties containing TC significantly reduced (P < 0.05) E. coli O157:H7 counts, by >5.0 log CFU/g, relative to the reduction in controls cooked to the same temperatures. The D-values at 60 and 65 °C of E. coli O157:H7 in TC-treated patties (1.85 and 0.08 min, respectively) were significantly lower (P < 0.05) than the corresponding D-values for the organism in control patties (2.70 and 0.29 min, respectively). TC-treated patties were more color stable and showed significantly lower lipid oxidation (P < 0.05) than control samples. TC enhanced the heat sensitivity of E. coli O157:H7 and could potentially be used as an antimicrobial for ensuring pathogen inactivation in undercooked patties. However detailed sensory studies will be necessary to determine the acceptability to consumers of TC in ground beef patties.     

The growth,survival and thermal inactivation of Escherichia coli O157:H7 in a traditional South African sausage

This study investigated the growth and survival of Escherichia coli O157:H7 inoculated into boerewors models with (B + P) and without (B − P) sulphur dioxide preservative at a low (L) and high (H) inoculum followed by storage at 0, 4 and 10 °C for 10 days. The pathogen’s thermal inactivation at 50, 60, 65 and 70 °C was also evaluated in B + P. The B − P at both low and high inocula had significantly higher recoveries at all temperatures compared to B + P. The BL + P and BH + P had significant reductions in recoveries at 0 °C, declining to below detectable limits at days 8 and 10, respectively. At 4 °C, the BL + P and BH + P recoveries declined significantly at day 10. At 10 °C, significant increases were observed from days 0 to day 10 in both models and at low and high inocula. At 0 °C, the BL − P and BH − P treatments had significant declines in recoveries. The combination of sulphur dioxide preservative and low temperature demonstrated the best efficacy against E. coli O157:H7 survival. Thermal inactivation of E. coli O157:H7 was 60 min at 60 °C, 80 s at 65 °C and 60 s at 70 °C. This study demonstrated that E. coli O157:H7 can survive in boerewors with and without preservative and is more sensitive to heat treatment at 70 °C.     

Control of Escherichia coli O157:H7 in corn silage with or without various inoculants: Efficacy and mode of action

This study aimed to evaluate the effectiveness of 3 commercial bacterial inoculants at controlling Escherichia coli O157:H7 in corn silages during ensiling and feedout phases of silage production. A second objective was to determine whether the inoculants exhibited and transferred antibacterial activity against E. coli O157:H7 to the silages. Chopped corn forage was ensiled after treatment with the following: distilled water (control); 5 × 10⁵ cfu/g of E. coli O157:H7 (EC); EC and 1 × 10⁶ cfu/g of Pediococcus pentosaceus and Propionibacterium freudenreichii (EC+BII); EC and 1 × 10⁶ cfu/g of Lactobacillus buchneri (EC+LB); and EC and 1 × 10⁶ cfu/g of L. buchneri and P. pentosaceus (EC+B500). Each treatment was ensiled in triplicate in mini silos for 3, 7, 31, and 82 d and analyzed for pH and E. coli O157:H7 counts. Samples from d 82 were also analyzed for volatile fatty acids, lactate, and aerobic stability. Antibacterial activity of inoculants and silages was determined by the Kirby-Bauer disc diffusion test. The pH of silages from all treatments decreased below 4 within 3 d of ensiling and remained low until d 82. Therefore, E. coli O157:H7 was not detected in silages after any of the ensiling durations. Applying inoculants containing L. buchneri resulted in less lactate, more acetate, and greater aerobic stability compared with the control. Applying EC+BII containing P. freudenreichii did not increase propionate or aerobic stability. Subsamples of d 82 silages were reinoculated with 1 × 10⁵ cfu/g of E. coli O157:H7 either immediately after silo opening on d 82 or after 144 h of aerobic exposure (d 88), and E. coli were enumerated 24 h later. All silages reinoculated with the pathogen on d 82 had similar, low pH values (<4) and no E. coli were detected 24 h later. Control, EC, and EC+BII silages reinoculated with the pathogen after 144 h of aerobic exposure had relatively greater pH values (4.71, 5.67, and 6.03, respectively) and E. coli counts (2.87, 6.73, and 6.87 log cfu/g, respectively) 24 h later, whereas those treated with L. buchneri had low pH values (<4) and undetectable (EC+B500) or 10-fold lower (1.97, cfu/g; EC+LB) E. coli counts. All pure cultures of commercial bacterial inoculants exhibited antibacterial activity independent of pH against E. coli O157:H7, but the pH-independent activity did not persist in the treated silages, suggesting that E. coli elimination from silages was mediated by pH reduction.     

Antibacterial effects of natural tenderizing enzymes on different strains of Escherichia coli O157:H7 and Listeria monocytogenes on beef

This study determined the efficacy of actinidin and papain on reducing Listeria monocytogenes and three mixed strains of Escherichia coli O157:H7 populations on beef. The average reduction of E. coli O157:H7 was greater than that of L. monocytogenes and higher concentrations of either protease yielded greater reduction in bacterial populations. For instance, actinidin at 700 mg/ml significantly (p ≤ 0.05) reduced the population of L. monocytogenes by 1.49 log cfu/ml meat rinse after 3 h at 25 & 35 °C, and by 1.45 log cfu/ml rinse after 24 h at 5 °C, while the same actinidin concentration significantly reduced the populations of three mixed strains of E. coli O157:H7 by 1.81 log cfu/ml rinse after 3 h at 25 & 35 °C, and 1.94 log cfu/ml rinse after 24 h at 5 °C. These findings suggest that, in addition to improving the sensory attributes of beef, proteolytic enzymes can enhance meat safety when stored at suitable temperatures.     

The physiologic state of Escherichia coli O157:H7 does not affect its detection in two commercial real-time PCR-based tests

Multiplex real-time PCR detection of Escherichia coli O157:H7 is an efficient molecular tool with high sensitivity and specificity for meat safety assurance. The Biocontrol GDS^® and DuPont Qualicon BAX^®-RT rapid detection systems are two commercial tests based on real-time PCR amplification with potential applications for quantification of specific E. coli O157:H7 gene targets in enriched meat samples. However, there are arguments surrounding the use of these tests to predict pre-enrichment concentrations of E. coli O157:H7, as well as arguments pertaining to the influence of non-viable cells causing false positive results. The present study attempts to illustrate the effects of different bacterial physiologic states and the presence of non-viable cells on the ability of these systems to accurately measure contamination levels of E. coli O157:H7 in ground beef. While the PCR threshold cycle (C_T) values of these assays showed a direct correlation with the number of bacteria present in pure cultures, this was not the case for ground beef samples spiked with various levels of injured or healthy cells. Furthermore, comparison of post-enrichment cell densities of bacteria did not correlate with injured or healthy cell numbers inoculated before enrichment process. Ground beef samples spiked with injured or healthy cells at different doses could not be distinguished by C_T values from either assay. In addition, the contribution of nonviable cells in generating positive real-time PCR signals was investigated using both assays on pre-enriched and post-enriched beef samples, but only if inoculated at levels of 10⁶ cells/sample or higher, which are levels not typically seen in ground beef.     

Effect of cooking procedures of kiymali pide,a traditional Turkish fast-food,on destruction of Escherichia coli O157:H7

The objective of the present study was to obtain data about cooking time and temperature of kiymali pide in the restaurants and to investigate thermal inactivation of E. coli O157:H7 during experimental kiymali pide making. A field study was conducted in randomly selected 23 of 87 pide restaurants. Processing parameters including oven temperature, cooking period and post-cooking temperature were determined. Kiymali pide samples were prepared using ground beef filling experimentally inoculated with E. coli O157:H7 (7.6 log₁₀ CFU/g). Pide samples were cooked at a conventional oven at 180 °C for 180, 240, 270, 300 and 330 s. Results of the current study suggest that cooking kiymali pide at 180 °C for at least 330 s (5.5 min) may provide sufficient food safety assurance (≥ 6 log₁₀ CFU/g) for E. coli O157:H7.     

Antibacterial activity of oregano and thyme essential oils against Listeria monocytogenes and Escherichia coli O157:H7 in feta cheese packaged under modified atmosphere

The antibacterial activity of the essential oils (EO) of oregano and thyme added at doses of 0.1 or 0.2 and 0.1 ml/100 g, respectively, to feta cheese inoculated with Escherichia coli O157:H7 or Listeria monocytogenes was investigated during cheese storage under modified atmosphere packaging (MAP) of 50% CO₂ and 50% N₂ at 4 °C. Compositional analysis showed that the predominant phenols were carvacrol and thymol for both EO. In control feta inoculated with the pathogens and stored under MAP, results showed that E. coli O157:H7 and L. monocytogenes strains survived up to 32 and 28 days of storage. However, in feta cheese treated with oregano EO at the dose of 0.1 ml/100 g, E. coli O157:H7 or L. monocytogenes survived up to 22 and 18 days, respectively, whereas at the dose of 0.2 ml/100 g up to16 or 14 days, respectively. Feta cheese treated with thyme EO at 0.1 ml/100 g showed populations of E. coli O157:H7 or L. monocytogenes not significantly different (P > 0.05) than those of feta cheese treated with oregano at 0.1 ml/100 g. Although both essential oils exhibited equal antibacterial activity against both pathogens, the populations of L. monocytogenes decreased faster (P < 0.05) than those of E. coli O157:H7 during the refrigerated storage, indicating a stronger antibacterial activity of both essential oils against the former pathogen.     

Influence of Simulated Apple Cider Composition on the Heat Resistance of Escherichia coli O157:H7

In light of recent outbreaks involving Escherichia coli O157:H7 in unpasteurized apple cider, this study was undertaken to determine the effect of apple cider composition on the heat resistance of this pathogen, and to develop regression models to predict its inactivation under varying conditions of pH (2.82-4.06), titratable acidity (TA) (31.14-111.80), and Brix (8.86-15.32). Heating was conducted in capillary tubes submerged in a stirred oil bath, and viability was determined by plating on tryptic soy agar. A central rotatable composite design was used which consisted of 18 treatment combinations at each of three heating temperatures (52, 54 and 56°C). The time (min) for a 2-log reduction (cT_2D) and a 4-log reduction (T_4D) were calculated for each of the 54 treatment combinations by fitting a smoothing spline to the survival curve. Two regression models were developed to predict the effect of the factors on T_2D andT_4D , and regression coefficients of 0.95 and 0.90 were obtained, respectively. The effects of pH and TA on T_2D and T_4D were significant (P\le0.05) at all heating temperatures. Increasing Brix to 15 ° had a protective effect on E. coliO157:H7. The interaction between pH and TA was significant, as was the combined effect of Brix and pH. The combination of Brix and TA was not significant. The results support the use of a nonparametric model such as a smoothing spline for the analysis of survival curves when parametric models are not adequate.     

Multiplex fiber optic biosensor for detection of Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica from ready-to-eat meat samples

Listeria monocytogenes, Escherichia coli O157:H7 and Salmonella enterica are the most common foodborne bacterial pathogens and are responsible for many outbreaks. Therefore, multiplex detection of these three using a single assay platform is highly desirable. The objective was to develop and optimize a fiber optic sensor for simultaneous detection of these three from food. The streptavidin coated optical waveguides were immobilized with biotinylated polyclonal antibodies and exposed to the bacterial suspensions or enriched food samples for 2 h. Pathogens were detected after reacting with Alexa-Fluor 647-labeled monoclonal antibodies. Ready-to-eat beef, chicken and turkey meats were inoculated with each pathogen (∼100 cfu/25 g), enriched in SEL (Salmonella, E. coli, Listeria), a multipathogen selective enrichment broth for 18 h and tested with the biosensor. The biosensor was able to detect each pathogen, individually or in a mixture with very little cross-reactivity. The limit of detection for the sensor was ∼10³ cfu/ml for all three pathogens. Furthermore, the biosensor successfully detected each pathogen, grown in a mixture from enriched meat samples under 24 h. The pathogen presence was further verified by PCR and immunofluorescence assay. The multiplex fiber optic sensor shows promise for detection of the three pathogens if present in the same sample eliminating the use of multiple single pathogen detection platforms.     

Inhibition of polymerase chain reaction for the detection of Escherichia coli O157:H7 and Salmonella enterica on walnut kernels

The aim of this study was to determine whether Escherichia coli O157:H7 can be reliably detected and isolated from walnut kernels using standard methods of analysis. The limit of detection approached 1 cell per analytical unit (25 g) for E. coli O157:H7 on walnut kernels enriched in modified tryptic soy broth with 20 μg/ml novobiocin and plating onto selective agar media. The presence of PCR inhibitors in walnut kernels was indicated by the failure to detect E. coli O157:H7 from culture positive enrichment broths analysed by PCR, with two separate polymerase and reagent compositions (Dupont BAX E. coli O157:H7 MP system, Promega GoTaq Green for stx) and three methods of template preparation (DuPont BAX, Qiagen DNeasy, Bio-Rad InstaGene). PCR inhibition was overcome by 1:100 dilution in TE buffer of the DNeasy or InstaGene template. PCR inhibition was not relieved by dilution of the BAX template. Similar results were observed for walnut kernels inoculated with Salmonella enterica and analysed for invA, indicating that PCR inhibition is not specific to the organism or primer/template. These results indicate that analysis of walnut kernels for pathogens should be with culture based methods or use protocols for DNA template preparation modified to remove or dilute inhibitors and the need for internal amplification controls in PCR methods.     

Pulsed UV light as an intervention strategy against Listeria monocytogenes and Escherichia coli O157:H7 on the surface of a meat slicing knife

The main objective of this work was to explore the applicability of the Intense Light Pulses (ILP) for decontamination of a stainless steel meat contact surface, exemplified by a slicing knife, as a function of time between contamination and decontamination, number of light pulses applied, and the prior contact with different meat matrices. Listeria monocytogenes and Escherichia coli O157:H7 were chosen as the challenge microorganisms. The ILP system was a laboratory-scale four-lamp batch system generating 3 J/cm² with an input voltage of 3000 V. The results obtained demonstrate successful application of ILP treatment for reduction of L. monocytogenes and E. coli O157:H7 on a surface of stainless steel slicing knife. The inactivation effectiveness depended on the type of meat product that was in the contact with the treated surface and on the time between the contamination and the ILP treatment. Statistical analysis showed the significant interaction between the time and type of meat product on the effectiveness of ILP treatment. The highest effectiveness of the ILP (the complete inactivation of 6.5 log CFU/side of knife) was obtained when the knife surface was in contact with the products containing lower fat and protein content and when it was treated with pulsed light as fast as possible after the contamination (within 60 s). The decontamination efficacy of ILP treatment could not be improved by multiple light pulses if lost due to the extended time between the moment of contamination and ILP treatment. Results showed that the suggested approach can be very effective as an intervention strategy along meat processing lines preventing cross-contamination between the equipment and the final product.