Survival of Escherichia coli O157:H7 in soil and on carrots and onions grown in fields treated with contaminated manure composts or irrigation water

Many foodborne outbreaks of enterohemorrhagic Escherichia coli O157:H7 infection have been associated with the consumption of contaminated vegetables. On-farm contaminations through contaminated manure or irrigation water application were considered likely sources of the pathogen for several outbreaks. Field studies were done to determine the survival of E. coli O157:H7 on two subterranean crops (carrots and onions), and in soil fertilized with contaminated manure compost or irrigated with contaminated water. Three different types of composts, PM-5 (poultry manure compost), 338 (dairy manure compost) and NVIRO-4 (alkaline stabilized dairy manure compost), and irrigation water were inoculated with an avirulent strain of E. coli O157:H7 at 10⁷ cfu g⁻¹ and 10⁵ cfu ml⁻¹, respectively. A split-plot block design plan was used for each crop, with five treatments (one without compost, three with each of the three composts, and one without compost but with contaminated irrigation water applied) and five replicates for a total of 25 plots, each measuring 1.8×4.6 m², for each crop. Composts were applied to soil as a strip at a rate of 4.5 metric tons ha⁻¹ before carrots and onions were sown. Contaminated irrigation water was sprayed once on the vegetables at the rate of 2 l per plot for this treatment 3 weeks after carrots and onions were sown. E. coli O157:H7 survived in soil samples for 154–196 days, and was detected for 74 and 168 days on onions and carrots, respectively. E. coli O157:H7 survival was greatest in soil amended with poultry compost and least in soil containing alkaline-stabilized dairy manure compost. Survival profiles of E. coli O157:H7 on vegetables and soil samples, contaminated either by application of contaminated compost or irrigation water, were similar. Hence, preharvest contamination of carrots and onions with E. coli O157:H7 for several months can occur through both contaminated manure compost and irrigation water.     

Determination of the efficacy of ultrasound in combination with essential oil of oregano for the decontamination of Escherichia coli on inoculated lettuce leaves

Recent outbreaks related to fresh produce have shown that there is a need to develop new efficient and effective decontamination technologies that protect consumers' safety. Ultrasound and assisted ultrasound, i.e., the combination of ultrasound with another decontamination technology has been shown to be effective against bacteria. In this study equal surfaces of free-bacteria of Romaine lettuce were inoculated with Escherichia coli O157:H7 NCTC 12900. Leaves were then treated with an ultrasound probe system (26 kHz, 90 μm, 200 W, 14 mm Ø). Same processing time (300 s) was applied with continuous and pulsed modes of: (i) 10 s on/6 s off, (ii) 5 s on/5 s off and (iii) 2 s on/8 s off. Thus, total treatment durations were 5, 8, 10 and 25 min. Moreover, concentrations of essential oil (i.e. 0.010% v/v, 0.014% v/v. 0.018% v/v, 0.022% v/v and 0.025% v/v) of oregano were tested, operating with continuous and 2 s on/8 s off pulsed mode. The structure of treated samples was also analysed by SEM and light microscopy. Continuous ultrasound treatments led to a reduction of 2.65 ± 0.23 log CFU/cm² of E. coli on the lettuce. No significant differences were found among the tested pulsed and continuous modes. In addition no significant differences were found between injured and no-injured cells among all the applied treatments on the leaves of the lettuce. Application of the different concentrations of EO alone, at the levels mentioned previously reduced the bacteria on the surface of the lettuce. Less than 2 logs of total inactivation (on the lettuce and the treated water) were achieved when different concentrations of EO were tested alone. Assisted ultrasound enhanced the levels of microbial reduction on the surface of the lettuce at concentrations higher than 0.010% (v/v) of oregano EO. Significant differences were found at 0.018%, 0.022% and 0.025% (v/v) both in continuous and pulsed US modes when compared with samples treated only with US. Same concentrations of EO combined with continuous or pulsed mode of US reduced the level of E. coli in water below the limit of detection. When continuous or pulse mode of US was combined with 0.025% (v/v) of EO of oregano the result was synergetic. Images reported neither structural differences nor damage of the leaves among treated samples and controls. Concluding, the effectiveness of the assisted ultrasound process was dependent on the processing time rather than on the different configurations (continuous or on/off) or the total treatment duration. Furthermore, EO combined with US could work synergistically on enhancing the inactivation of the tested bacteria.     

The impact of extreme weather events on Salmonella internalization in lettuce and green onion

Salmonella internalization is an important issue in raw vegetable consumption because washing usually cannot remove or inactivate the internalized pathogens effectively. In this study, the impact of extreme weather events, drought and heavy rains, caused by climate change on the internalization of Salmonella Typhimurium was investigated. Two leafy green fresh produce, iceberg lettuce and green onion were chosen. Rhizosphere soil inoculation was conducted to mimic the contamination routes via soil and then root uptake. Most internalized S. Typhimurium were found in lettuce leaves and in the root portions of green onion under all three irrigation conditions (optimal, drought, storm). In general, high concentration of soil inoculation facilitated the internalization level in both lettuce and green onion. Under extreme weather conditions, the internalization of S. Typhimurium in lettuce occurred when the soil was contaminated with a high level of bacteria (8–9 log colony forming unit (CFU)/g soil) and under these conditions, the internalization level was higher than the lettuce grown at the optimal water condition, except with 8 log CFU/g contamination (storm). Under drought, the results showed high variation, but the level of internalization of S. Typhimurium in lettuce increased by 16 times (1.21 log CFU/g) and 27 times (1.43 log CFU/g) compared to the optimally irrigated group when the soil was contaminated with 8 log and 9 log CFU/g soil, respectively. Ten-fold increased internalization was observed in the over-irrigated lettuce leaves when the soil was contaminated with 9 log CFU/g soil. The green onion samples showed ~ 4 log CFU/g green onion of S. Typhimurium internalization when exposed to high level of contamination (> 7 log CFU/g soil), which is a much higher internalization rate than the lettuce (average 2–3 log CFU/g). However, from the green onion experiments, no apparent patterns of water stress that affect on the levels on the Salmonella internalization were observed.     

Monitoring of Escherichia coli O157:H7 in food samples using lectin based surface plasmon resonance biosensor

A novel surface plasmon resonance (SPR) biosensor using lectin as bioreceptor was developed for the rapid detection of Escherichia coli (E. coli) O157:H7. The selective interaction of lectins with carbohydrate components from bacterial cells surface was used as the recognition principle for the detection. Five types of lectins from Triticum vulgaris, Canavailia ensiformis, Ulex europaeus, Arachis hypogaea, and Maackia amurensis, were employed to evaluate the selectivity of the approach for binding E. coli O157:H7 effectively. A detection limit of 3 × 10³ cfu mL^?1 was obtained for determination of E. coli O157:H7 when used the lectin from T. vulgaris as the binding molecule. Furthermore, the proposed biosensor was used to detect E. coli O157:H7 in real food samples. Results showed that the lectin based SPR biosensor was sensitive, reliable and effective for detection of E. coli O157:H7, which hold a great promise in food safety analysis.     

Inactivation of Escherichia coli O157:H7 and Listeria monocytogenes in milk by caprylic acid and monocaprylin

Listeria monocytogenes and Escherichia coli O157:H7 are major foodborne pathogens implicated in various outbreaks involving pasteurized or unpasteurized milk, and various dairy products. The objective of this study was to determine the antibacterial effect of caprylic acid (CA, C_8:0) and its monoglyceride, monocaprylin (MC) on L. monocytogenes and E. coli O157:H7 in whole milk. A five-strain mixture of E. coli O157:H7 or L. monocytogenes was inoculated in autoclaved milk (10⁶ CFU/ml) containing 0, 25, or 50 mM of CA or MC. At 37°C, all the treatments, excepting 25 mm CA, reduced the population of both pathogens by approximately 5.0 log CFU/ml in 6 h. At 24 h of storage at 8°C, MC at both levels and CA at 50 mM decreased L. monocytogenes and E. coli O157:H7, respectively by >5.0 log CFU/ml. At 48 h of 4°C storage, populations of L. monocytogenes and E. coli O157:H7 were decreased to below detection level (enrichment negative) by 50 mm of MC and CA, respectively. Results indicate that MC could potentially be used to inhibit L. monocytogenes and E. coli O157:H7 in milk and dairy products, but sensory studies need to be conducted before recommending their use.     

The influence of lactoperoxidase,heat and low pH on survival of acid-adapted and non-adapted Escherichia coli O157:H7 in goat milk

In hot climates where quality of milk is difficult to control, a lactoperoxidase (LP) system can be applied in combination with conventional preservation treatments at sub-lethal levels to inhibit pathogenic microbes. This study investigated the effect of combined heat treatments (55 °C, 60 °C and 72 °C) and milk acidification (pH 5.0) on survival of acid-adapted and non-adapted Escherichia coli O157:H7 strains UP10 and 1062 in activated LP goat milk. Heat treatment at 72 °C eliminated E. coli O157:H7. Acid-adapted strains UP10 and 1062 cells showed resistance to combined LP and heat at 60 °C in fresh milk. The inhibition of acid-adapted and non-adapted E. coli O157:H7 in milk following combined LP-activation, heat (60 °C) and milk acidification (pH 5.0) suggests that these treatments can be applied to reduce E. coli O157:H7 cells in milk when they occur at low numbers (<5 log₁₀ cfu mL^?1) but does not eliminate E. coli O157:H7 to produce a safe product.     

Effect of mild heat pre-treatment with alkaline electrolyzed water on the efficacy of acidic electrolyzed water against Escherichia coli O157:H7 and Salmonella on Lettuce

Cut lettuce dip-inoculated with Escherichia coli O157:H7 and Salmonella was treated with alkaline electrolyzed water (AlEW) at 20°C for 5 min, and subsequently washed with acidic electrolyzed water (AcEW) at 20°C for 5 min. Pre-treatment with AlEW resulted in an approximate 1.8 log₁₀ cfu/g reduction of microbial populations, which was significantly (p⩽0.05) greater than microbial reductions resulting from other pre-treatment solutions, including distilled water and AcEW. Repeated AcEW treatment did not show a significant bacterial reduction. Mildly heated (50°C) sanitizers were compared with normal (20°C) or chilled (4°C) sanitizers for their bactericidal effect. Mildly heated AcEW and chlorinated water (200 ppm free available chlorine) with a treatment period of 1 or 5 min produced equal reductions of pathogenic bacteria of 3 log₁₀ and 4 log₁₀ cfu/g, respectively. The procedure of treating with mildly heated AlEW for 5 min, and subsequent washing with chilled (4°C) AcEW for period of 1 or 5 min resulted in 3–4 log₁₀ cfu/g reductions of both the pathogenic bacterial counts on lettuce. Extending the mild heat pre-treatment time increased the bactericidal effect more than that observed from the subsequent washing time with chilled AcEW. The appearance of the mildly heated lettuce was not deteriorated after the treatment. In this study, we have illustrated the efficacious application of AlEW as a pre-wash agent, and the effective combined use of AlEW and AcEW.     

Inspection of lymph nodes for caseous lymphadenitis and its effect on the density of microbes on sheep carcasses

This study aimed to measure the amount of microbial contamination caused by inspecting the lymph nodes of adult sheep carcasses for caseous lymphadenitis (CLA). Surface swabs from carcasses pre-inspection (N = 296) and post-inspection (N = 296) were obtained for enumeration of indicator organisms at three commercial abattoirs. At the scapular site, inspection doubled the probability of detecting E. coli (Pr before = 0.35, Pr after = 0.67) and increased the expected count of E. coli from 2 cfu/cm² to 13 cfu/cm². Inspection at the rump site increased the probability of detecting E. coli by 1.1 times (Pr before = 0.84, Pr after = 0.93) and increased the expected count from 32 cfu/cm² to 45 cfu/cm². Effects were also observed for Enterobacteriaceae and total viable count. The findings show that routine inspection of adult sheep carcasses for CLA has a detrimental impact on carcass microbiological traits.     

Development of an immunosensor based on surface plasmon resonance for enumeration of Escherichia coli in water samples

An immunosensor for the rapid, sensitive and selective detection of generic Escherichia coli in water samples was developed on the basis of surface plasmon resonance (SPR). Antibodies against E. coli were immobilized on a sensor surface and water samples with different concentrations of E. coli were injected to the flow cell. The changes in the response unit (RU) due to the binding of different concentrations of bacteria were computed and a linear correlation (R² = 0.976) was obtained between log E. coli concentration and the change in the RU with a working range of 9 × 10¹ and 1.8 × 10⁵ cfu ml⁻¹. The complete regeneration of the sensor surface was realized by using 1% SDS solution. The selectivity of the developed sensor was examined with Enterobacter aerogenes and Enterobacter dissolvens which did not produce any significant response. The ability of the developed sensor to detect E. coli in real water samples was investigated and the results were closed to that obtained from plate counting method. Based on these results, the developed immunosensor can be employed for rapid, label-free, sensitive and selective detection of E. coli in water samples.     

Inactivation of Escherichia coli O157:H7 by cinnamic aldehyde purified from Cinnamomum cassia shoot

Escherichia coli O157:H7 is a pathogen, which causes the hemorrhagic colitis, hemolytic uremic syndrome and thrombotic thrombocytopenic purpura in humans. Control of the bacterial cells in foods is an important factor to reduce outbreaks of the foodborne diseases. In this study, cinnamic aldehyde possessing antimicrobial activity against the bacterial cells was purified from the extract of cinnamon (Cinnamomum cassia Blume) shoot by sequential fractionation with various solvents and silica gel column chromatography. When E. coli O157:H7 cells were incubated at 37°C for 12 h in the presence of 500 μg ml⁻¹ of the purified from cinnamic aldehyde, the viable counts decreased dramatically (from 4.9×10⁶ to 1.0×10² cfu ml⁻¹). In the presence of 1000 μg ml⁻¹ of the substance, most of the cells were killed after 2 h of incubation suggesting that the antimicrobial activity of cinnamic aldehyde is bacteriocidal in E. coli. Scanning electron microscopic observations revealed that the bacterial cells treated with the cinnamic aldehyde suffered from severe damages in their surface structure. Minimal inhibitory concentration of the cinnamic aldehyde was determined to be 250 μg ml⁻¹ against E. coli strains O157:H7 and O26 or 500 μg ml⁻¹ against strains ATCC11105 and O111.     

The growth and survival of Escherichia coli O157:H7 on minced bison and pieces of bison meat stored at 5 and 10 °C

This study investigated the growth and survival of Escherichia coli O157:H7 on minced and whole pieces of bison meat. Growth curves of native microflora, including Pseudomonas spp. and Enterobacteriaceae were also generated. A marked E. coli O157:H7 strain was inoculated onto minced and whole pieces of bison meat at an initial level of 1.5 log₁₀ cfu g⁻¹. The inoculated meat was stored at either 5 °C for 28 days or 10 °C for 21 days. Survival, but no growth, of E. coli O157:H7 was observed on both forms of bison meat stored at 5 °C, while significant growth of the organism was observed at 10 °C. E. coli O157:H7 counts on whole pieces were generally higher than counts observed on minced bison meat, and reached their highest population by 14 days, with a total increase of 3.36 log₁₀ cfu g⁻¹ on whole pieces and 2.12 log₁₀ cfu g⁻¹on minced bison meat stored at 10 °C. Under the same storage temperature, Pseudomonas spp. and total counts displayed similar growth patterns on both pieces and minced bison meat, while the Enterobacteriaceae showed a slower growth rate. This study showed that the growth of E. coli O157:H7 on bison meat is similar to that observed in studies of beef.     

Comparison of multiple chemical sanitizers for reducing Salmonella and Escherichia coli O157:H7 on spinach (Spinacia oleracea) leaves

Effectiveness of multiple chemical sanitizers on the reduction of Salmonella spp. and Escherichia coli O157:H7 on spinach was compared. Fresh spinach (Spinacia oleracea) was inoculated with a bacterial suspension containing multiple strains of rifampin-resistant Salmonella and E. coli O157:H7. Inoculated spinach leaves were treated with a water wash or water wash followed by 2% L-lactic acid at 55 °C, peroxyacetic acid (80 mg/L), calcium hypochlorite (200 mg/L), ozonated water (mg/L) or ClO₂ gas (1.2 or 2.1 mg/L). The l-lactic acid produced a 2.7 log CFU/g reduction for E. coli O157:H7 and a 2.3 log CFU/g reduction for Salmonella, statistically significant compared to water wash alone (P < 0.05), which resulted in a reduction of 0.7 log CFU/g for both pathogens. These findings indicate that 2% l-lactic acid at 55 °C may be an effective treatment for reducing pathogens on spinach leaves.     

Modeling inactivation kinetics and occurrence of sublethal injury of a pulsed electric field-resistant strain of Escherichia coli and Salmonella Typhimurium in media of different pH

A study of the effect of pulsed electric fields (PEF) on the kinetics of inactivation and the occurrence of cell damage in Escherichia coli O157:H7 and Salmonella Typhimurium 878 treated in McIlvaine buffer covering a range from pH 3.5 to 7.0 was conducted. Mathematical equations based on the Weibull distribution were developed to describe the influence of the electric field strength, treatment time and pH of the treatment medium on the lethality and generation of cell damage of both Gram negative pathogenic bacteria after the application of PEF treatments. E. coli O157:H7 was more PEF resistant than Salmonella Typhimurium at all pH investigated. PEF resistance of E. coli was influenced by the pH but the pH hardly affected the PEF resistance of Salmonella Typhimurium 878. After 150 μs at 35 kV/cm, 1 and 5 log₁₀ cycles of inactivation of E. coli O157:H7 were observed in the range of pH 3.5–4.5 and 5.5–6.5, respectively. Cell damage increased with the field strength and treatment time. A maximum cell damage level of 4.2 and 2.7 log₁₀ cycles for E. coli O157:H7 and Salmonella Typhimurium was observed respectively after a treatment of 30 kV/cm at pH 3.5. PEF induced cell damage was not detected at pH higher than 5.0 for both microorganisms. The developed equations can be applied to design combining processes which can increase the lethality of PEF or to reduce the intensity of PEF treatments to achieve a determine level of microbial inactivation.Industrial relevanceThis study demonstrates that when the influence of several factors on the microbial behavior is investigated, the development of mathematical models is a very useful tool to evaluate the influence of each parameter and their interactions. In this study, it has been mathematically described for first time the influence of the pH of the treatment medium and the occurrence of sublethal injury in a wide range of electric field strengths and treatment times in two Gram negative pathogenic bacteria, Escherichia coli O157:H7 and Salmonella Typhimurium 878. These models would also be of interest for engineering design, evaluation and optimization of PEF process as a new technique for food preservation.     

Polymorphonuclear neutrophils and Escherichia coli proteases involved in proteolysis of casein during experimental E. coli mastitis

An Escherichia coli mastitis model was used to characterize enzymes involved in bovine mammary tissue damage and proteolysis in milk. One-quarter each of four cows were inoculated with a suspension (10⁴ cfu mL⁻¹) of E. coli P4:O32. Blood and milk were collected before inoculation and for 216 h afterwards. Intracellular elastase, collagenase and cathepsin activities were measured by flow cytometry of peripheral blood leukocytes and milk polymorphonuclear neutrophils (PMNs). Leukopenia occurred in peripheral blood 9 h after infection, concomitant with an increase in somatic cell count in milk. Milk PMNs had lower activity of cathepsins and collagenase than peripheral blood PMNs. In parallel, milk samples were studied by zymography, and several proteases were detected in mastitic milk. These activities increased after infection, to reach a peak in 6 h. However, total protease profiles and plasmin activities differed. It was concluded that proteases released by PMNs and E. coli contribute to proteolysis of casein during mastitis, as well as plasmin.     

High pressure–low temperature processing of beef: Effects on survival of internalized E. coli O157:H7 and quality characteristics

High pressure–low temperature (HPLT) processing was investigated to achieve Escherichia coli O157:H7 inactivation in non-intact, whole muscle beef while maintaining acceptable quality characteristics. Beef semitendinosus was internally inoculated with a four strain E. coli O157:H7 cocktail and frozen to − 35 °C, then subjected to 551 MPa for 4 min (HPLT). Compared to frozen, untreated control (F), HPLT reduced microbial population by 1.7 log colony forming units (CFU)/g on selective media and 1.4 log on non-selective media. High pressure without freezing (551 MPa/4 min/3 °C) increased pH and lightness while decreasing redness, cook yield, tenderness, and protein solubility. Aside from a 4% decrease in cook yield, HPLT, had no significant effects on quality parameters. It was demonstrated that HPLT treatment reduces internalized E. coli O157:H7 with minimal effect on quality factors, meaning it may have a potential role in reducing the risk associated with non-intact red meat.Industrial relevanceIn the current work, high pressure (551 MPa, 4 min) was applied to beef semitendinosus while it was at subfreezing temperatures (<− 30 °C). Most studies utilizing this high pressure–low temperature (HPLT) process employ subzero capable thermostatic high pressure equipment, which currently has no commercial equivalent. Successful HPLT runs were completed in this study using more conventional temperature control (1–3 °C) on pilot scale (20 L) high pressure processing equipment. The process yielded E. coli O157:H7 reductions of 1.4–1.7 log colony forming units (CFU)/g, which, while lower than conventional high pressure processing (HPP), may be sufficient to eliminate O157 populations typical of non-intact, whole muscle beef. Various quality factors, including color, purge losses and cooked tenderness, were unaffected by HPLT, while an equivalent HPP process at nonfreezing temperatures (551 MPa, 3 °C) induced color change (loss of redness), increased cook losses and decreased cooked tenderness compared to the control and HPLT beef. Producers of non-intact, whole muscle (blade tenderized or brine injected) meat, especially those that ship and sell frozen products, may look to HPLT processes to improve food safety.     

Inactivation of food spoilage bacteria and Escherichia coli O157:H7 in phosphate buffer and orange juice using dynamic high pressure

This study aimed to evaluate the potential of dynamic high pressure (DHP) technology to inactivate pathogenic and spoilage microflora in orange juice. Escherichia coli O157:H7 ATCC 35150, Lactobacillus plantarum ATCC 14917, Leuconostoc mesenteroides ATCC 23386 and two orange juice isolates: Saccharomyces cerevisiae and Penicillium ssp. were subjected individually to different DHP treatments. The effectiveness of DHP treatment was first evaluated in phosphate buffered saline (PBS) before application in orange juice samples. The inactivation efficacy of DHP depended on the pressure applied and the number of passes. It was more efficient against Gram-negative strains than Gram-positives. Complete inactivation and 5 log reduction of E. coli O157:H7 were achieved in orange juice at 200 MPa after 5 and 3 passes at 25 °C, respectively. Lower inactivation was obtained with Penicillium ssp. (4 log), S. cerevisiae (2.5 log), L. plantarum (2.3 log) and L. mesenteroides (1.6 log). The gathered results revealed the potential of DHP to inactivate all the tested microorganisms and then, it could constitute a promising alternative technology for cold pasteurization of fruit juices.     

Ultrasound treatments improve the microbiological quality of water reservoirs used for the irrigation of fresh produce

Irrigation water has been highlighted as a source of microbial contamination in produce. Water treatment has been recommended as an intervention strategy to reduce microbial risks associated to irrigation water. Commercial water treatments mostly depend on chemical agents; although growers search for greener alternatives to chemical biocides. Ultrasounds (US) have been proposed as an environmentally friendly technology for irrigation water. In the present study, the suitability of two US treatments (20 kHz: US20 and 40 kHz: US40 at a specific energy (Es) of 745 J/L) and one chlorine treatment (1–2 ppm free chlorine) was evaluated and compared to the untreated control. Five water reservoirs belonging to five commercial intensive farms were selected as representative of irrigation practices generally used in south of Europe. All tested water treatments were able to reduce microbial loads, including Escherichia coli (0.5–0.6 log units), to values that were accepted in most of the recommended guidelines of good agricultural practices (≤ 2 log units). The obtained reductions were lower than those previously reported for these water treatment technologies in lab-scale tests. High microbial reductions are commonly obtained in laboratory studies, yielding impressive results. However, when the same treatments are applied under real commercial conditions, microbial reductions are usually less impressive. All water treatments were able to reduce COD of irrigation water when compared to the untreated control. COD reductions obtained using chlorine (≥ 430 mg/L) and US 20 (~ 100 mg/L) were higher than those observed using US 40 (< 50 mg/L). The impact of the water quality on the efficacy of US treatments was evaluated in two types of water including surface water and treated wastewater. It was found that the quality of the irrigation water significantly influences the efficacy of the ultrasound treatment. Correlations between indicator parameters have been also evaluated. Obtained results showed that high algae counts were well correlated with high levels of coliforms and E. coli. It could be concluded that US can be proposed as an alternative water treatment to chemical treatments to preserve microbial quality of irrigation water stored in water reservoirs reducing the environmental impact.     

Enterobacteriaceae in beef products from retail outlets in the Republic of Ireland and comparison of the presence and counts of E. coli O157:H7 in these products

This study investigated the prevalence and numbers of Enterobacteriaceae in minced beef and beef burgers purchased from supermarkets and butcher shops in the Republic of Ireland (RoI). Samples (n=1303) collected between June 2001 and April 2002 from every county in the RoI (∼60 per county) were examined for the presence of Enterobacteriaceae using method BS 5763. Overall, in the 43 beef products in which E. coli O157:H7 was present the Enterobacteriaceae counts ranged from 0.52 to 6.98 log₁₀ cfu g⁻¹. There was no correlation between the number of Enterobacteriaceae and the presence of E. coli O157:H7. There were no significant differences between Enterobacteriaceae numbers in fresh, unpackaged, minced beef samples from butcher shops and supermarkets, or in fresh, unpackaged, beef burgers from butcher shops and supermarkets. However, there were significant differences among the numbers of Enterobacteriaceae detected in different minced beef products. The numbers of Enterobacteriaceae in fresh, unpackaged, minced beef (6.54–6.98 log₁₀ cfu g⁻¹) were considerably higher than in preprepared or prepackaged minced beef (2.95–3.62 log₁₀ cfu g⁻¹).     

Inactivation of Escherichia coli O157:H7, Salmonella and human norovirus surrogate on artificially contaminated strawberries and raspberries by water-assisted pulsed light treatment

This study investigated the inactivation of Escherichia coli O157:H7, Salmonella and murine norovirus (MNV-1), a human norovirus surrogate, on strawberries and raspberries using a water-assisted pulsed light (WPL) treatment. The effects of combinations of WPL treatment with 1% hydrogen peroxide (H₂O₂) or 100 ppm sodium dodecyl sulfate (SDS) were also evaluated. Strawberries and raspberries were inoculated with E. coli O157:H7 and treated by WPL for 5–60 s. E. coli O157:H7 on both strawberries and raspberries was significantly reduced in a time-dependent manner with 60-s WPL treatments reducing E. coli O157:H7 by 2.4 and 4.5 log CFU/g, respectively. Significantly higher reductions of E. coli O157:H7 were obtained using 60-s WPL treatment than washing with 10 ppm chlorine. Compared with washing with chlorine, SDS and H₂O₂, the combination of WPL treatment with 1% H₂O₂ for 60 s showed significantly higher efficacy by reducing E. coli O157:H7 on strawberries and raspberries by 3.3- and 5.3-log units, respectively. Similarly, Salmonella on strawberries and raspberries was inactivated by 2.8- and 4.9-log units after 60-s WPL–H₂O₂ treatments. For decontamination of MNV-1, a 60-s WPL treatment reduced the viral titers on strawberries and raspberries by 1.8- and 3.6-log units, respectively and the combination of WPL and H₂O₂ did not enhance the treatment efficiency. These results demonstrated that the WPL treatment can be a promising chemical-free alternative to chlorine washing for decontamination of berries destined for fresh-cut and frozen berry products. WPL–H₂O₂ treatment was the most effective treatment in our study for decontamination of bacterial pathogens on berries, providing an enhanced degree of microbiological safety for berries.     

Transcriptional and functional responses of Escherichia coli O157:H7 growing in the lettuce rhizoplane

Lettuce and spinach are increasingly implicated in foodborne illness outbreaks due to contamination by Escherichia coli O157:H7. While this bacterium has been shown to colonize and survive on lettuce leaf surfaces, little is known about its interaction with the roots of growing lettuce plants. In these studies, a microarray analyses, mutant construction and confocal microscopy were used to gain an understanding of structure and function of bacterial genes involved in the colonization and growth of E. coli O157:H7 on lettuce roots. After three days of interaction with lettuce roots, 94 and 109 E. coli O157:H7 genes were significantly up- and down-regulated at least 1.5 fold, respectively. While genes involved in biofilm modulation (ycfR and ybiM) were significantly up-regulated, 40 of 109 (37%) of genes involved in protein synthesis were significantly repressed. E. coli O157:H7 was 2 logs less efficient in lettuce root colonization than was E. coli K12. We also unambiguously showed that a ΔycfR mutant of E. coli O157:H7 was unable to attach to or colonize lettuce roots. Taken together these results indicate that bacterial genes involved in attachment and biofilm formation are likely important for contamination of lettuce plants with Shiga toxin-producing E. coli strains.