title: Survival of Listeria monocytogenes cells and the effect of extended frozen storage (-20°C) on the expression of its virulence gene.
abstract: Listeria monocytogenes is the main bacteria incriminated in contaminating cold storage food and ready-to-eat products. Survival of four L. monocytogenes food isolates was examined during freezing and cold storage. Slices of artisanal cheese were inoculated with Listeria strains and incubated at -20 °C. Their survival rate was recorded during the storage period. Then, transcript levels of four virulence genes (hlyA, iap, fri, and flaA) were evaluated using a semiquantitative reverse transcriptase PCR. Our results revealed that after 6 months of frozen storage, the number of L. monocytogenes cells had declined by 2.04 ± 0.1 log10 colony-forming units (CFU) g(-1), 2.52 ± 0.1 log10 CFU g(-1), and 2.58 ± 0.1 log10 CFU g(-1) for the strains S2, S3, and S4, respectively. Our data revealed that all the studied genes (hlyA, iap, fri, and flaA) were expressed after 6 months of incubation in artisanal cheese at -20 °C, and the transcript level has been affected by the factor freezing, whether for the reference strain ATCC 19115 or for other isolates. The iap gene expression was decreased for the four strains after 6 months of storage, and hlyA expression rate was consistently slightly lower. Transcript levels of fri and flaA genes were consistently higher in L. monocytogenes cells before cold exposure than in stressed cells and were significantly affected by the freezing process.
authors: Laboratoire d'Analyses, Traitement et Valorisation des Polluants de l'Environnement et des Produits, Faculté de Pharmacie, rue Avicenne 5000, Monastir, Tunisia. rbs_23@yahoo.fr
authors: Rihab
authors: R
authors: Ben Slama
authors: Hanene
authors: H
authors: Miladi
authors: Kamel
authors: K
authors: Chaieb
authors: Amina
authors: A
authors: Bakhrouf
mesh_terms: D018070:Biological Specimen Banks; D002470:Cell Survival / Q000502:physiology; D015925:Cryopreservation / Q000379:methods*; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D008089:Listeria monocytogenes / Q000166:cytology* / Q000502:physiology*; D037521:Virulence Factors / Q000096:biosynthesis* / Q000235:genetics*
chemical_list: D037521:Virulence Factors