Publications by authors named "Lisbeth Mehli"

5 Publications

  • Page 1 of 1

Occurrence, diversity and temperature-dependent growth kinetics of Aeromonas spp. in lettuce.

Int J Food Microbiol 2020 Dec 31;335:108852. Epub 2020 Aug 31.

Norwegian University of Science and Technology, NTNU, 7491 Trondheim, Norway. Electronic address:

Bagged, pre-cut and prewashed lettuce products are marketed as ready to eat. This concept poses a food safety concern, due to lack of efficient hurdles to eliminate possible microbial contaminants from the fresh produce and/or the processing itself. Aeromonas spp. are potential foodborne pathogens that are frequently isolated from lettuce. High counts of, e.g., A. hydrophila have been found in retail ready-to-eat (RTE) vegetable salads. The aim of this study was to assess the general microbiological quality, the occurrence and diversity of potential human pathogenic mesophilic Aeromonas spp. of retail RTE lettuce products. Additionally, temperature-dependent growth kinetic parameters of Aerobic Plate Counts (APC) and Aeromonas spp. in one selected RTE lettuce product, rocket lettuce, were quantified by performing storage experiments at 4 °C, 8 °C and 12 °C. The Aeromonas isolates were further characterized regarding pathogenic traits and phylogenetic relationship. The overall hygienic quality of the lettuce products was unsatisfactory, as 60% of the products had an APC level higher than 7.0 log CFU/g. Presumptive Aeromonas spp. were detected in 52% of the samples, levels ranging from approximately 2.0-6.0 log CFU/g. Significantly lower counts of APC and Aeromonas spp. were found in uncut and unwashed products. Presumptive Aeromonas spp. were able to proliferate in rocket lettuce stored at 4 °C (μ = 0.39 ± 0.06/d and μ = 0.43 ± 0.05/d for lettuce from producers A and B, respectively), and μ was approximately 2× higher at 8 °C and 3× higher at 12 °C. Eighty-four percent of the collected isolates were identified as A. media, based on partial gyrB sequencing. Additionally A. salmonicida and A. bestiarum were detected. The pathogenic potential in this material was high, most of the isolates harbored at least one of the toxin genes, act, ast, alt.
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http://dx.doi.org/10.1016/j.ijfoodmicro.2020.108852DOI Listing
December 2020

Assessment of microbiological quality of retail fresh sushi from selected sources in Norway.

J Food Prot 2015 May;78(5):977-82

Department of Food Technology, Sør-Trøndelag University College, N-7004 Trondheim, Norway.

Retail fresh sushi is gaining popularity in Europe. This study was conducted to investigate the microbiological quality of selected samples of fresh sushi with a shelf life of 2 to 3 days offered as complete meals in Norwegian supermarkets. Analysis of aerobic plate counts in 58 sushi samples from three producers revealed large variations in microbiological quality, and 48% of the analyzed sushi boxes were rated as unsatisfactory (> 6.0 log CFU/g). Mesophilic Aeromonas spp. was detected in 71% of the samples. In a follow-up study, we collected products and raw materials directly from the production facility of one producer and observed a significant decrease (P < 0.01) in aerobic plate counts compared with the initial sampling. The observed difference between products purchased in stores compared with those collected directly from the factory suggests that poor temperature control during distribution and display in stores leads to reduced microbiological quality. Microbiological analysis of the sushi ingredients revealed that potentially pathogenic bacteria such as mesophilic Aeromonas spp. or bacteria belonging to the Enterobacteriaceae can be introduced into sushi through both raw vegetables and fish. The results highlight the importance of high quality ingredients and proper temperature control to ensure stable quality and safety of these food products.
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http://dx.doi.org/10.4315/0362-028X.JFP-14-480DOI Listing
May 2015

A case study from the interaction of strawberry and Botrytis cinerea highlights the benefits of comonitoring both partners at genomic and mRNA level.

New Phytol 2005 Nov;168(2):465-74

Sør-Trøndelag University College, Faculty of Food Science and Medical Technology, Trondheim, Norway.

Strawberry Fragaria x ananassa (cv. Korona) was inoculated with Botrytis cinerea by dipping berries in a conidial suspension. Colonization by the pathogen was monitored using real-time PCR, ELISA and ergosterol assays, the first showing the highest sensitivity. The expression of pathogen beta-tubulin and six polygalacturonases (Bcpg1-6) and three host defence genes (polygalacturonase-inhibiting protein (FaPGIP) and two class II chitinases) were monitored using real-time RT-PCR. The maximum transcript levels of the host defence genes occurred at 16 h postinoculation (hpi) at the presumed initial penetration stage. The unique transcript profile of Bcpg2 over the 96-h incubation time and its high transcript levels relative to those of the other Bcpgs at 8-24 hpi suggest that the gene has a specific role in the penetration stage. Bcpg1 was expressed constitutively at a relatively high level in actively growing mycelia throughout the experimental period. Comparison of the transcript profiles indicated that Bcpg1 and Bcpg3-6 were coordinately regulated.
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http://dx.doi.org/10.1111/j.1469-8137.2005.01526.xDOI Listing
November 2005

Quantification of allele-specific expression of a gene encoding strawberry polygalacturonase-inhibiting protein (PGIP) using Pyrosequencing.

Plant J 2005 Feb;41(3):493-500

Plant Research International, Wageningen University and Research Centre, PO Box 16, 6700 AA Wageningen, The Netherlands.

Recent studies indicate that allele-specific differences in gene expression are a common phenomenon. The extent to which differential allelic expression exists might be underestimated, due to the limited accuracy of the methods used so far. To demonstrate allele-specific expression, we investigated the transcript abundance of six individual, highly homologous alleles of a polygalacturonase-inhibiting protein gene (FaPGIP) from octoploid strawberry (Fragaria x ananassa). We applied the highly quantitative Pyrosequencing method which, for the gene under study, detected allele frequency differences as small as 4.0 +/- 2.8%. Pyrosequencing of RT-PCR products showed that one FaPGIP allele was preferentially expressed in leaf tissue, while two other alleles were expressed in a fruit-specific way. For fruits that were inoculated with Botrytis cinerea a strong increase in overall FaPGIP gene expression was observed. This upregulation was accompanied by a significant change in FaPGIP allele frequencies when compared with non-treated fruits. Remarkably, in the five cultivars tested, the allele frequency in cDNA from the inoculated fruits was similar to that in genomic DNA, suggesting uniform upregulation of all FaPGIP alleles present as a result of pathogenesis-related stress. The results demonstrate that when Pyrosequencing of RT-PCR products is performed, novel allele-specific gene regulation can be detected and quantified.
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http://dx.doi.org/10.1111/j.1365-313X.2004.02299.xDOI Listing
February 2005

A gene encoding a polygalacturonase-inhibiting protein (PGIP) shows developmental regulation and pathogen-induced expression in strawberry.

New Phytol 2004 Jul;163(1):99-110

Plantebiosenteret, Department of Biology, NTNU, 7491 Trondheim, Norway.

•  Polygalacturonase-inhibiting proteins (PGIPs) have been demonstrated to play a role in host defence in several plants. •  The PGIP now cloned from strawberry (Fragaria × ananassa) showed a high degree of homology to other fruit PGIPs. The gene expression of strawberry PGIP was monitored in healthy leaves, flowers and fruit at different maturity stages. PGIP transcript levels were also analysed following fruit inoculation with the fungal pathogen Botrytis cinerea in strawberry cultivars displaying variation in susceptibility. •  Healthy mature berries showed the highest constitutive PGIP gene expression levels compared with leaves, flowers and immature fruit, indicating that the gene is developmentally regulated. Among the cultivars studied ('Elsanta', 'Korona', 'Polka', 'Senga sengana', 'Tenira'), 'Polka' had the highest constitutive expression level of PGIP. After inoculation with B. cinerea, all five cultivars displayed a significant induction of PGIP gene expression, but the differences between them were not statistically significant. •  The high induction of the PGIP gene after inoculation with B. cinerea indicates that PGIP has a role in defence of strawberry.
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http://dx.doi.org/10.1111/j.1469-8137.2004.01088.xDOI Listing
July 2004