Effects of sodium nitrite reduction, removal or replacement on cured and cooked meat for microbiological growth, food safety, colon ecosystem, and colorectal carcinogenesis in Fischer 344 rats

Epidemiological and experimental evidence indicated that processed meat consumption is associated with colorectal cancer risks. Several studies suggest the involvement of nitrite or nitrate additives via N-nitroso-compound formation (NOCs). Compared to the reference level (120 mg/kg of ham), sodium nitrite removal and reduction (90 mg/kg) similarly decreased preneoplastic lesions in F344 rats, but only reduction had an inhibitory effect on Listeria monocytogenes growth comparable to that obtained using the reference nitrite level and an effective lipid peroxidation control. Among the three nitrite salt alternatives tested, none of them led to a significant gain when compared to the reference level: vegetable stock, due to nitrate presence, was very similar to this reference nitrite level, yeast extract induced a strong luminal peroxidation and no decrease in preneoplastic lesions in rats despite the absence of NOCs, and polyphenol rich extract induced the clearest downward trend on preneoplastic lesions in rats but the concomitant presence of nitrosyl iron in feces. Except the vegetable stock, other alternatives were less efficient than sodium nitrite in reducing L. monocytogenes growth

Caractérisation de souches de portage asymptomatique de Listeria monocytogenes isolées chez l'Homme : Evaluation des capacités invasives et étude de leur survie en milieu acide et en présence de sels biliaires

While the gut is the final reservoir separating the external environment from the host tissues, it can harbor strains of Listeria monocytogenes following ingestion of contaminated food. The criteria required to reach the intestine are related to the stresses encountered in the host. The first criterion analyzed is the ability of the strain to activate its glutamate decarboxylase (GAD) at acidic pH because this system would protect the strain from the acidity of the stomach. Fecal carriage strains are particularly resistant to the acidity of the medium simulating gastric fluids in the presence of glutamate. Few foodborne strains possess levels of GAD activity comparable to those observed for asymptomatic carriage strains and strains responsible for human listeriosis cases. The resistance of L. monocytogenes to bile salts is common to all the strains studied, regardless of their origin. The study of the invasive capacities of the 14 strains of asymptomatic carriage in the host cell showed that 10 strains of fecal carriage had an attenuated level of virulence on the 14-day-old embryonated chicken egg in contrast to the strains linked to epidemic or sporadic episodes. Five of these asymptomatic carriage strains have reduced abilities to enter the Caco-2 epithelial cell in culture. Internalin A, a bacterial virulence protein involved in epithelial cell entry, appears to be the deficient factor for these 5 strains. Analysis of partial sequences of the inlA gene allowed the detection of point mutations responsible for the appearance of premature stop codons and the production of the truncated forms of Internalin A observed by Western-blot. The use of PCR-RFLP on the variable regions of the inlA gene of strains of various origins allowed us to detect the presence of this deficiency in strains of food origin. The frequency of this type of potentially non-invasive strains in food could therefore explain, at least in part, the existence of asymptomatic carriage and the relatively low incidence of listeriosis cases in proportion to the estimated frequency of ingested L. monocytogenes.Alors que l’intestin est le dernier réservoir qui sépare le milieu extérieur des tissus de l’hôte, il peut héberger des souches de Listeria monocytogenes suite à l’ingestion d’aliments contaminés. Les critères requis pour parvenir dans l’intestin sont liés aux stress rencontrés chez l’hôte. Le premier critère analysé est la capacité de la souche à activer sa glutamate décarboxylase (GAD) à pH acide car ce système protégerait la souche de l’acidité de l’estomac. Les souches de portage fécal résistent particulièrement bien à l’acidité du milieu simulant les fluides gastriques en présence de glutamate. Peu de souches d’origine alimentaire possédent des niveaux d’activité GAD comparables à ceux observés pour les souches de portage asymptomatique et les souches responsables de cas de listériose chez l’Homme. La résistance de L. monocytogenes aux sels biliaires est par contre un caractère commun à l’ensemble des souches étudiées quelle que soit leur origine. L’étude des capacités invasives des 14 souches de portage asymptomatique dans la cellule hôte a montré que 10 souches de portage fécal avaient un niveau de virulence atténué sur l’œuf embryonné de poulet de 14 jours contrairement aux souches liées à des épisodes épidémiques ou sporadiques. Cinq de ces souches de portage asymptomatique ont des capacités réduites d’entrée dans la cellule épithéliale Caco-2 en culture. L’Internaline A, une protéine de virulence bactérienne impliquée dans l’entrée de la bactérie dans la cellule épithéliale, apparaît être le facteur déficient pour ces 5 souches. L’analyse de séquences partielles du gène inlA a permis de déceler des mutations ponctuelles responsables de l’apparition de codons stop prématurés et de la production des formes tronquées d’Internaline A observées par Western-blot. L’utilisation de la PCR-RFLP sur les régions variables du gène inlA de souches d’origines diverses nous a permis de détecter la présence de cette déficience chez des souches d’origine alimentaire. La fréquence de ce type de souches potentiellement non invasives dans l’aliment pourrait donc expliquer au moins en partie, l’existence du portage asymptomatique et l’incidence relativement faible de cas de listérioses en proportion de la fréquence estimée de L. monocytogenes ingérées

Caractérisation de souches de portage asymptomatique de Listeria monocytogenes isolées chez l'homme (évaluation des capacités invasives et étude de leur survie en milieu acide et en présence de sels biliaires)

DIJON-BU Sciences Economie (212312102) / SudocSudocFranceF

Use of PCR-restriction fragment length polymorphism of inlA for rapid screening of Listeria monocytogenes strains deficient in the ability to invade Caco-2 cells

International audienceA PCR-restriction fragment length polymorphism (RFLP) method was developed in order to screen a large number of strains for impaired adhesion to epithelial cells due to expression of truncated InlA. inlA polymorphism was analyzed by PCR-RFLP in order to correlate inlA PCR-RFLP profiles and production of truncated InlA. Thirty-seven Listeria monocytogenes strains isolated from various sources, including five noninvasive and two invasive reference strains, were screened. Two endonucleases (AluI and Tsp509I) were used, and they generated five composite profiles. Thirteen L. monocytogenes isolates were characterized by two specific PCR-RFLP profiles similar to PCR-RFLP profiles of noninvasive reference strains previously described as strains that produce truncated InlA. Ten of the 13 isolates showed low abilities to invade human epithelial Caco-2 cells. However, 4 of the 13 isolates were able to invade Caco-2 cells like reference strains containing complete InlA. Sequencing of inlA and Western blot analysis confirmed that truncated InlA was expressed in the 10 L. monocytogenes strains which were isolated from food. This PCR-RFLP method allowed us to identify 10 new strains expressing a truncated internalin. Based on the results obtained in this study, the PCR-RFLP method seems to be an interesting method for rapidly screening L. monocytogenes strains deficient in the ability to invade Caco-2 cells when a sizeable number of strains are studied

Screening of glutamate decarboxylase activity and bile salt resistance of human asymptomic carriage, clinical, food, and environmental isolates of Listeria monocytogenes

International audienceFollowing consumption, stomach acidity is the first major barrier encountered by thefood-borne pathogen Listeria monocytogenes. Analysis of low pH sensitivity and glutamatedecarboxylase (GAD) acid resistance system of 14 isolates of L. monocytogenes carriedasymptomatically by humans showed that levels of GAD activity was subjected to strainvariation. Similar variations were observed for strains responsible of 18 listeriosis, whereas incomparison, 13 strains isolated from food and from food-processing plant environmentshowed lower GAD activity. Following survival of the stomach barrier, L. monocytogenesalso has to resist to bile salts encountered in the small intestine. Analysis revealed that allstrains tested were able to grow in presence of bile salts with concentrations as high as thoseencountered in the small intestine and had the previously identified Bile Salt Hydrolase(BSH) activity. Strain variation was observed but there was no relationship between the originof the strains and the ability to degrade bile salts

Truncated Internalin A and Asymptomatic Listeria monocytogenes Carriage: In Vivo Investigation by Allelic Exchange

Allelic exchange of the region coding for the C terminus of InlA between one epidemic (with an 80-kDa InlA) and one asymptomatic (with a 47-kDa InlA) carriage Listeria monocytogenes strain confirmed the need for this region for internalin entry in vitro. Interestingly, restoration of internalin A functionality did not result in full virulence in chicken embryo assays

Assessment of the pathogenic potential of two Listeria monocytogenes human faecal carriage isolates

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Expression of Truncated Internalin A Is Involved in Impaired Internalization of Some Listeria monocytogenes Isolates Carried Asymptomatically by Humans

Fourteen human carriage Listeria monocytogenes isolates were compared to sporadic and epidemic-associated human strains in order to ascertain the pathogenic behavior of these unrecognized asymptomatic strains. Experimental infection of 14-day-old chick embryos revealed that the majority of the carriage strains were attenuated for virulence. Of the 10 attenuated carriage strains, 5 were affected in their invasion capacities in vitro. Western blot analysis with antibody directed against InlA, the surface protein implicated in the internalization in host cells, allowed correlation between the ability of the carriage strains to enter Caco-2 cells and InlA expression. Indeed, these five carriage strains produced truncated forms of InlA. Four of the five truncated forms of InlA had an apparent molecular mass of 47 kDa. In order to assess the existence of a genetic lineage, partial sequences of inlA gene of these four strains were compared and revealed that they had a high degree of sequence conservation at the gene (99.86%) and amino acid (100%) levels. Comparison of their nucleotide sequences with that of the corresponding segment of inlA from EGD-e and Scott A strains, taken as epidemic references, showed more divergence. Taken together, these observations suggest the presence of specific traits that characterize L. monocytogenes strains isolated during asymptomatic carriage. Some of these traits could provide some explanations about the determinants that make them unable to cause systemic human infection

Impact d'un régime hyper lipidique sur le microbiote intestinal au cours de la carcinogenèse mammaire : effetsur la réponse immunitaire anti-tumorale chez la souris C57BL/6

Impact d'un régime hyper lipidique sur le microbiote intestinal au cours de la carcinogenèse mammaire : effetsur la réponse immunitaire anti-tumorale chez la souris C57BL/6. Journée NACRe/Partenariat 201