| 1. |
- Mogren, Lars, et al.
(author)
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The hurdle approach-A holistic concept for controlling food safety risks associated with pathogenic bacterial contamination of leafy green vegetables. A review
- 2018
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In: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 9:AUG
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Research review (peer-reviewed)abstract
- Consumers appreciate leafy green vegetables such as baby leaves for their convenience and wholesomeness and for adding a variety of tastes and colors to their plate. In Western cuisine, leafy green vegetables are usually eaten fresh and raw, with no step in the long chain from seed to consumption where potentially harmful microorganisms could be completely eliminated, e.g., through heating. A concerning trend in recent years is disease outbreaks caused by various leafy vegetable crops and one of the most important foodborne pathogens in this context is Shiga toxin-producing Escherichia coli (STEC). Other pathogens such as Salmonella, Shigella, Yersinia enterocolitica and Listeria monocytogenes should also be considered in disease risk analysis, as they have been implicated in outbreaks associated with leafy greens. These pathogens may enter the horticultural value network during primary production in field or greenhouse via irrigation, at harvest, during processing and distribution or in the home kitchen/restaurant. The hurdle approach involves combining several mitigating approaches, each of which is insufficient on its own, to control or even eliminate pathogens in food products. Since the food chain system for leafy green vegetables contains no absolute kill step for pathogens, use of hurdles at critical points could enable control of pathogens that pose a human health risk. Hurdles should be combined so as to decrease the risk due to pathogenic microbes and also to improve microbial stability, shelf-life, nutritional properties and sensory quality of leafy vegetables. The hurdle toolbox includes different options, such as physical, physiochemical and microbial hurdles. The goal for leafy green vegetables is multi-target preservation through intelligently applied hurdles. This review describes hurdles that could be used for leafy green vegetables and their biological basis, and identifies prospective hurdles that need attention in future research.
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| 2. |
- Alsanius, Beatrix, et al.
(author)
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Dining in Blue Light Impairs the Appetite of Some Leaf Epiphytes
- 2021
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In: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 12
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Journal article (peer-reviewed)abstract
- Background: The phyllosphere is subjected to fluctuating abiotic conditions. This study examined the phenotypic plasticity (PP) of four selected non-phototrophic phyllosphere bacteria [control strain: Pseudomonas sp. DR 5-09; Pseudomonas agarici, Bacillus thuringiensis serovar israeliensis (Bti), and Streptomyces griseoviridis (SG)] regarding their respiration patterns and surfactant activity as affected by light spectrum and nutrient supply.Methods: The PP of the strains was examined under four light regimes [darkness (control); monochromatic light-emitting diodes (LED) at 460 nm (blue) and 660 nm (red); continuously polychromatic white LEDs], in the presence of 379 substrates and conditions.Results: Light treatment affected the studied bacterial strains regarding substrate utilization (Pseudomonas strains > SG > Bti). Blue LEDs provoked the most pronounced impact on the phenotypic reaction norms of the Pseudomonas strains and Bti. The two Gram-positive strains Bti and SG, respectively, revealed inconsistent biosurfactant formation in all cases. Biosurfactant formation by both Pseudomonas strains was supported by most substrates incubated in darkness, and blue LED exposure altered the surface activity profoundly. Blue and white LEDs enhanced biofilm formation in PA in highly utilized C-sources. Putative blue light receptor proteins were found in both Pseudomonas strains, showing 91% similarity with the sequence from NCBI accession number WP_064119393.Conclusion: Light quality–nutrient interactions affect biosurfactant activity and biofilm formation of some non-phototrophic phyllosphere bacteria and are, thus, crucial for dynamics of the phyllosphere microbiome.
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| 3. |
- Alsanius, Beatrix, et al.
(author)
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E. coli:s dolda liv: sockersug och kurragömma
- 2016
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In: LTV-fakultetens faktablad.
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Other publication (pop. science, debate, etc.)abstract
- Frukt och grönsaker ingår i en hälsosam kost. Dessa konsumeras antingen i rå eller tillredd form. Ett ökat antal utbrott av tarmsmittor har dock relaterats till frukt och grönsaker för direktkonsumtion eller konsumtion med minimal tillredning, både i Sverige och utomlands. Ofta förknippas magsmittor på frukt och grönt med importerade varor. Det tragiska utbrottet av EHEC, en mycket aggressiv grupp av E. coli (serotyp O157:H7), sensommaren 2005 satte problematiken på den svenska kartan. För att skapa förutsättningar för att förebygga spridning av humanpatogena sjukdomsalstrare (såsom EHEC, Salmonella, Campylobacter) under odlingen till produkten har vi undersökt hur E. coli O157:H7 förökas på ytan av bladgrönsaker och i vilken omfattning den förmår att krypa in och gömma sig i bladvävnaden. Invasion i bladvävnaden innebär att den blir oåtkomlig vid tvättning. För bladgrönt fann vi att E. coli O157:H7- kan invadera både oskadd växtvävnad och växtvävnad som skadats antingen mekaniskt eller genom sjukdomsangrepp, - förmår att överleva och att växa till på ytan av intakta och tryckskadade, skurna och strimlade blad och - tillväxten är växtspecifik.Glukos och fruktos var de främsta sockerarterna på bladytan av intakta eller tryckskadade blad. Glukos, fruktos, sukros och galaktos förekom i stora mängder på skurna resp. sönderdelade blad. Ett mycket starkt samband mellan tillväxt av E. coli och sockerhalten konstaterades.Våra resultat visar att hög hygien måste råda i hela produktionskedjan från jord till bord. Att skölja grönsakerna innan förtäring har begränsad effekt och når inte de skadeorganismerna som har trängt in i växtvävnaden. Studien har genomförts inom ramen av Tvärlivs-projekt "Risker för humanpatogener i frukt och grönt i en globaliserad värld och strategier att bemästra dem", samt Partnerskap Alnarp projektet "Förekomst av tarmsmittor i bladgrönt under processing", båda i samarbete med Sydgrönt ek. för.
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| 4. |
- Gharaie, Samareh, et al.
(author)
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Light spectrum modifies the utilization pattern of energy sources in Pseudomonas sp. DR 5-09
- 2017
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In: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 12
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Journal article (peer-reviewed)abstract
- Despite the overruling impact of light in the phyllosphere, little is known regarding the influence of light spectra on non-phototrophic bacteria colonizing the leaf surface. We developed an in vitro method to study phenotypic profile responses of bacterial pure cultures to different bands of the visible light spectrum using monochromatic (blue: 460 nm; red: 660 nm) and polychromatic (white: 350-990 nm) LEDs, by modification and optimization of a protocol for the Phenotype MicroArray (TM) technique (Biolog Inc., CA, USA). The new protocol revealed high reproducibility of substrate utilization under all conditions tested. Challenging the non-phototrophic bacterium Pseudomonas sp. DR 5-09 with white, blue, and red light demonstrated that all light treatments affected the respiratory profile differently, with blue LED having the most decisive impact on substrate utilization by impairing respiration of 140 substrates. The respiratory activity was decreased on 23 and 42 substrates under red and white LEDs, respectively, while utilization of one, 16, and 20 substrates increased in the presence of red, blue, and white LEDs, respectively. Interestingly, on four substrates contrasting utilization patterns were found when the bacterium was exposed to different light spectra. Although non-phototrophic bacteria do not rely directly on light as an energy source, Pseudomonas sp. DR 5-09 changed its respiratory activity on various substrates differently when exposed to different lights. Thus, ability to sense and distinguish between different wavelengths even within the visible light spectrum must exist, and leads to differential regulation of substrate usage. With these results, we hypothesize that different light spectra might be a hitherto neglected key stimulus for changes in microbial lifestyle and habits of substrate usage by non-phototrophic phyllospheric microbiota, and thus might essentially stratify leaf microbiota composition and diversity.
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| 5. |
- Lindblom, Tobias, et al.
(author)
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Processing of leafy vegetables matters: Damage and microbial community structure from field to bag
- 2021
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In: Food Control. - : Elsevier BV. - 0956-7135 .- 1873-7129. ; 125
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Journal article (peer-reviewed)abstract
- Leafy vegetables undergo abiotic and biotic stresses, and a series of processing steps that cause mechanical injury. Breaching the epidermis alters phyllosphere structural and nutrient conditions, resulting in successional shifts in leaf microbiota and entry of human pathogens. This study examined damage during processing of baby leaves (Swiss chard, spinach) and concomitant microbial successional events. Machine-harvesting, washing, and packaging caused major phyllosphere perturbations, with increasing levels of leaf damage. Older leaves showed most damage, but plant species was influential. Diversity estimates of bacterial and fungal communities revealed shifts in microbiota post-harvest, particularly after the washing step. Relative abundance of Pseudomonadaceae and Enterobacteriaceae increased from field to bag. Bacterial species specific to different harvesting and processing steps replaced core microbiota species. While processing is unavoidable, procedures that mitigate leaf damage can enhance shelf-life and food safety.
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| 6. |
- Mulaosmanovic, Emina, et al.
(author)
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Size Matters: Biological and Food Safety Relevance of Leaf Damage for Colonization of Escherichia coli O157:H7 gfp
- 2021
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In: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 11
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Journal article (peer-reviewed)abstract
- This study examined the biological and food safety relevance of leaf lesions for potential invasion of food pathogens into the plant tissue (internalization). This was done by determining the role of artificial leaf damage in terms of damaged leaf area on proliferation of E. coli O157:H7 gfp+. In a two-factorial experiment, unwashed fresh baby leaf spinach (Spinacia oleracea L.) was subjected to four damage levels (undamaged, low, moderate, high damage; factor 1) and three incubation intervals (0, 1, 2 days post-inoculation; factor 2). Individual leaves were immersed for 15 s in a suspension loaded with E. coli O157:H7 gfp+ (106 CFU × mL–1). The leaves were analyzed individually using image analysis tools to quantify leaf area and number and size of lesions, and using confocal laser scanning and scanning electron microscopy to visualize leaf lesions and presence of the introduced E. coli strain on and within the leaf tissue. Prevalence of E. coli O157:H7 gfp+ was assessed using a culture-dependent technique. The results showed that size of individual lesions and damaged leaf area affected depth of invasion into plant tissue, dispersal to adjacent areas, and number of culturable E. coli O157:H7 gfp+ directly after inoculation. Differences in numbers of the inoculant retrieved from leaf macerate evened out from 2 days post-inoculation, indicating rapid proliferation during the first day post-inoculation. Leaf weight was a crucial factor, as lighter spinach leaves (most likely younger leaves) were more prone to harbor E. coli O157:H7 gfp+, irrespective of damage level. At the high inoculum density used, the risk of consumers’ infection was almost 100%, irrespective of incubation duration or damage level. Even macroscopically intact leaves showed a high risk for infection. These results suggest that the risk to consumers is correlated with how early in the food chain the leaves are contaminated, and the degree of leaf damage. These findings should be taken into account in different steps of leafy green processing. Further attention should be paid to the fate of viable, but non-culturable, shiga-toxigenic E. coli on and in ready-to-eat leafy vegetables.
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