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The ability of acid-adapted (AA) and non-acid-adapted (NA) Salmonella enterica serovar Typhimurium definitive type 104 (DT104) strains to invade and multiply in mammalian cells in vitro and to survive
stress conditions was examined. DT104 and non-DT104 strains were grown in tryptic soy broth without glucose (NA) or in tryptic soy broth containing 1% glucose (AA) for 18 h at 37°C. The invasiveness
of DT104 strains in J774A.1 macrophage and Int407 intestinal cell lines was not more extensive than that of non-DT104 strains. In most cases, AA bacteria were less invasive than NA bacteria in both cell
lines. Confocal microscopy showed that both DT104 and non-DT104 strains replicated in the two cell lines. In related studies, the survival levels of three strains of AA and NA DT104 and a non-DT104 (LT2)
strain in 150 and 15 mM H2O2, 170 and 43 mM acetic acid, 2.6 M NaCl, 2.6 M NaCl containing 170 mM acetic acid, synthetic gastric fluid (SGF) at pH 2 and pH 3, and apple cider were
compared. For all four strains, acid adaptation did not result in increased survival in apple cider. After 15 days of storage at 4°C, reductions ranged from 1.96 to 4.1 log10 CFU/ml for AA
bacteria and from 0.48 to 1.34 log10 CFU/ml for NA bacteria from a starting level of ca. 7.00 log10 CFU/ml of cider. Neither AA nor NA DT104 strains were more resistant to NaCl, acetic
acid, H2O2, or SGF solutions than non-DT104 strain LT2. The level of AA bacteria was not appreciably reduced after exposure to SGF; however, the level of NA bacteria decreased to nondetectable
levels in SGF at pH 2 within 3 h of exposure. These results indicate that the DT104 strains examined were not more invasive, nor did they display increased survival in mammalian cells or increased resistance
to food environment stresses compared with non-DT104 strains. However, acid adaptation resulted in increased resistance to a low-pH gastric environment for all strains tested. These data indicate that DT104
strains are likely not more virulent or resistant to stresses relevant to foods than are non-DT104 Salmonella and that procedures used to inactivate or inhibit the growth of Salmonella in
foods are likely adequate for DT104 strains.
Document Type: Research Article
U.S. Department of Agriculture, Agricultural Research Service, Eastern Regional Research Center, 600 East Mermaid Lane, Wyndmoor, Pennsylvania
Publication date: July 1, 2003
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