Modélisation du développement de bactéries potentiellement altérantes ou biopréservatrices sur du boudin blanc conservé à différentes conditions de températures et analysées par microbiologie classique et métagénomique (ADNr 16S)

An important way to prevent the spoilage of food is the respect of the cold chain during the storage. While the temperature instructions are generally respected during process and distribution of food products, it is not always the case with the consumers. Indeed, a few persons reach the right temperature level required for a safe storage of foodstuffs in their refrigerator. Besides, the food can sometimes spend a few hours in ambient temperature between the buying in the supermarket and the storage in cold temperature. In this study, we propose to model the growth of microorganisms on white pudding, stored in different conditions of temperature that reflect the situations described above (constant 4°C, constant 8°C, constant 12°C, 1/3 4°C – 2/3 8°C, 1/3 4°C – breach during 4h at 20°C – 2/3 4°C and 1/3 4°C – breach during 4h at 20°C – 2/3 8°C. The product was surface inoculated with potential spoilage and biopreservative strains (Raoultella terrigena, Serratia quinivorans, Carnobacterium maltaromaticum, Lactobacillus oligofermentans, Lactobacillus nenjiangensis, Lactobacillus fuchuensis, Leuconostoc mesenteroides, lactococcus lactis and Lactobacillus graminis). Analyses by classical microbiology and V1-V3 16S rDNA metagenomics were done each day until the out of date of the food matrix. The transition from 4 to 8°C and the breach at 20°C during 4h have clearly boosted the growth of the microorganisms. The metagenomic analysis was a powerful tool to follow separately each population in each condition of storage. The results of this communication show the importance of keeping the foodstuffs in 4°C or lower in the refrigerator with the goal to avoid the spoilage or the development of pathogens and the potential of metagenomics for selection of biopreservative strains

The use of 16S rRNA gene metagenetic monitoring of refrigerated food products for understanding the kinetics of microbial subpopulations at different storage temperatures: the example of white pudding

In order to control food losses and wastage,monitoring the microbial diversity of food products, during processing and storage is important, as studies have highlighted the metabolic activities of somemicroorganismswhich can lead to spoilage. Knowledge of this diversity can be greatly improved by using a metagenetic approach based on high throughput 16S rRNA gene sequencing, which enables a much higher resolution than culture-based methods. Moreover, the Jameson effect, a phenomenon described by Jameson in 1962, is often used to classify bacterial strains within an ecosystem. According to this, we have studied the bacterial microbiota of Belgian white pudding during storage at different temperatures using culture-dependent and independent methods. The product was inoculated with a mix of dominant strains previously isolated from this foodstuff at the end of its shelf life (Carnobacterium maltaromaticum, Lactobacillus fuchuensis, Lactobacillus graminis, Lactobacillus oligofermentans, Lactococcus lactis, Leuconostoc mesenteroides, Raoultella terrigena and Serratia sp.). Daily during 16 days, the absolute abundance of inoculated strain was monitored by combining total count on plate agar and metagenetic analysis. The resultswere confirmed by qPCR analysis. The growth of each specieswasmodelled for each temperature conditions, representative of good or bad storage practices. These data allowed the bacterial strains subdivision into three classes based on criteria of growth parameters for the studied temperature: the “dominant”, the “subdominant” and the “inhibited” bacterial species, according to their maximal concentration (Nmax, log CFU/g), growth rate (μmax, 1/h) and time to reach the stationary phase (TRSP, days). Thereby, depending on the storage conditions, these data have permitted to follow intrinsically the evolution of each strain on the bacterial ecosystemof Belgianwhite pudding. Interestingly, it has shown that the reliability of the Jameson effect can be discussed. For example, at 4 °C when Lactococcus lactis and Serratia sp. stopped growth at day 12, at the same time Carnobacterium maltaromaticum reached its maximal concentration and entered its stationary phase. In opposition to this, it can be noticed that in the same condition, the “sub-dominant” organisms continued their growth independently of the “dominant” species behaviour. In this case, the Jameson effect was not illustrated. This pattern is described for all storage conditions with the same strain classifications. These results highlighted the importance of combining metagenetic analysis and classical methods, with modelling, to offer a new tool for studying the evolution ofmicroorganisms present in perishable foodwithin different environmental conditions.METAMODE

Optimization of serologic diagnosis of celiac disease in the pediatric setting

BACKGROUND: The clinical presentation of celiac disease (CD) varies between children. The objective of this study was to document the pre-test probability for CD based on symptoms and routine laboratory test and to evaluate the performance of two IgA anti-tissue transglutaminase (tTG) assays. We critically reviewed the concept of using multiples of the manufacturer's upper limit of normal (ULN), as proposed in the ESPGHAN guidelines (if IgA tTG is >10 times ULN, no biopsy is needed). METHODS: The retrospective study included 91 children with newly diagnosed CD and 605 controls (<16 years). All underwent upper endoscopy with small bowel biopsies. Four laboratory parameters and 16 symptoms were registered. All patients were tested for IgA anti-tTG antibodies with assays from Inova Diagnostics and Thermo Fisher Scientific. RESULTS: Some combinations of clinical symptoms and laboratory parameters had a high pre-test probability for CD, such as (combinations of) anorexia, failure to thrive, low ferritin level and elevated AST. The diagnostic performance of both IgA anti-tTG assays was excellent and comparable (no difference in ROC curve area under the curve). At a threshold that corresponds to a specificity of 100% (5 times ULN for Inova Diagnostics and 2 times ULN for Thermo Fisher), the sensitivity was 82% for both assays. At the 10 times ULN threshold, the sensitivity differed between the assays (77% vs. 57%), indicating that such threshold does not completely align interpretation across companies. CONCLUSIONS: Our study showed that some combinations of symptoms and aberrant laboratory parameters had a high pre-test probability. The use of the ESPGHAN non-biopsy approach could reduce small bowel biopsies, but thresholds for IgA-tTG levels are not aligned across assays and should be based on predefined likelihood ratios or specificity.status: publishe