Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 27, 2003
Publication Date: N/A
Interpretive Summary: Salmonella Typhimurium in the definitive type 104 (DT104) group is an important public health concern since it is resistant to multiple antibiotics, and since studies have shown that it may have a greater ability to cause disease than Salmonella that are not in the DT104 group (non-DT104). Studies are needed to determine if exposure to acidic conditions that may be encountered in foods can increase the ability of DT104 strains to cause disease and make the organism more resistant to stresses found in food environments and in the gastrointestinal tract. Results showed that the tolerance of Salmonella DT104 to exposure to the acidic environments of apple cider and acetic acid solutions, to hydrogen peroxide solutions, and to high salt solutions was not greater than that of non-DT104 Salmonella. The DT104 strains did not display an increased ability to invade and survive in mammalian cells compared to non-DT104 Salmonella. Acid-adapted DT104 and non-DT104 Salmonella were generally les tolerant to the applied stresses compared to non-acid-adapted bacteria; however, acid-adapted bacteria were more tolerant to acidic synthetic gastric fluid compared to non-acid-adapted Salmonella. This study establishes that the DT104 strains that were examined did not display increased resistance to food environment stresses and did not show a greater ability to cause disease compared to non-DT104 Salmonella. Exposure to acidic environments, however, increased the resistance of DT104 and non-DT104 Salmonella to the acidic gastric environment. Therefore, food processors should be aware that Salmonella exposed to acidic food environments may pose a greater public health risk than Salmonella exposed to non-acidic environments.
Technical Abstract: The ability of acid-adapted and non-acid-adapted Salmonella enterica serovar Typhimurum DT104 (DT104) to invade and multiply in mammalian cells and to survive stress conditions was examined. The DT104 and non-DT104 strains were grown in tryptic soy broth without glucose (non-acid-adapted, NA) or containing 1% glucose (acid-adapted, AA) for 18 h at 37C. The ability to invade and survive in J774A.1 and Int407 cell lines was similar in DT104 and non-DT104 strains, and AA bacteria were generally less invasive than NA bacteria. In related studies, survival of three strains of AA and NA DT104 and a non-DT104 strain (LT2) was compared in 150 mM 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. For all four strains, acid adaptation did not result in increased survival in apple cider. After 15 days of storage at 4C, reductions ranged from 1.96 to 4.1 log10 CFU/ml for AA bacteria compared to 0.48 to 1.34 log10 CFU/ml for NA bacteria from a starting level of 7.0 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 was not appreciably reduced after exposure to SGF; however, the level of NA decreased to non-detectable levels in SGF, pH 2 after 3 h of exposure. Thus, 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 to non-DT104 strains. However, compared to NA bacteria, AA bacteria showed increased resistance to a low pH gastric environment in all strains examined.