title: Listeria monocytogenes efficiently invades Caco-2 cells after low-temperature storage in broth and on deli meat.
abstract: The objective of this study was to investigate how various growth conditions influence the virulence of Listeria monocytogenes monitored by its ability to invade the epithelial cell lines Caco-2 and INT-407. The growth conditions examined were modified atmosphere-packaged deli meat and brain heart infusion broth (BHI) with and without salt. Five strains of L. monocytogenes were selected to investigate their invasiveness and all strains invaded Caco-2 cells at higher levels than INT-407 cells. Further, the clinical strains (3443 and 3734) were more invasive (p < 0.05) than the strains isolated from meat and food-processing environments (3008, 3126, and 4140) after grown in BHI at 30 degrees C. This attenuation could not be ascribed to a defective Internalin A as all strains encoded an intact inlA gene. To determine the influence of food products on virulence, the ability of L. monocytogenes to invade Caco-2 cells was compared after growth on a fermented sausage and on cured cooked ham to that of bacteria grown in BHI broth supplemented with salt. Samples were stored under chilling conditions for up to 4 weeks. The results showed no difference (p > 0.05) in invasiveness after 7 days at 10 degrees C in BHI broth or on sausage, whereas a slight increase (p < 0.05) was observed after incubation on ham for 2 and 4 weeks compared to that in BHI broth. Most importantly, our results show that L. monocytogenes efficiently invade Caco-2 cells even after 4 weeks of storage at chilled temperature. This is highly relevant for safety assessment of this organism in food as these conditions reflect storage of ready-to-eat food products in domestic refrigerators.
authors.affiliation: Department of Veterinary Disease Biology, Centre for Advanced Food Studies, Faculty of Life Sciences, University of Copenhagen, Frederiksberg C, Denmark. mhl@life.ku.dk
authors.forename: Marianne Halberg
authors.initials: MH
authors.lastname: Larsen
authors.forename: Anette Granly
authors.initials: AG
authors.lastname: Koch
authors.forename: Hanne
authors.initials: H
authors.lastname: Ingmer
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D001431:Bacteriological Techniques; D018938:Caco-2 Cells; D002460:Cell Line; D003080:Cold Temperature; D003470:Culture Media; D004847:Epithelial Cells / Q000382:microbiology; D005511:Food Handling; D005516:Food Microbiology; D006801:Humans; D007422:Intestines / Q000382:microbiology; D008089:Listeria monocytogenes / Q000235:genetics / Q000254:growth & development* / Q000472:pathogenicity*; D008088:Listeriosis / Q000382:microbiology; D008460:Meat / Q000382:microbiology; D008461:Meat Products / Q000382:microbiology; D013045:Species Specificity
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; C069761:internalin protein, Bacteria