Author
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Zaika, Laura |
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Submitted to: Meeting Abstract
Publication Type: Abstract Only Publication Acceptance Date: 5/2/2001 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: Bacterial survival at low pH depends not only on the pH value, but also on the type of acid and on storage temperature. Shigella, a major foodborne pathogen, is acid tolerant. We studied survival of Shigella flexneri strain 5348 in brain heart infusion broth (BHI) supplemented with organic acids. Media containing 0.04 acetic, citric, lactic, malic, or tartaric acid were adjusted to pH 4 with HC1 or NaOH. The control medium was BHI adjusted to pH 4 with HCI. Stationary phases cells were inoculated into media to give initial populations of 6 to 7 log 10 CFU/ml and incubated at 4, 19, 28, and 37 deg C. A two-phase linear inactivation model was applied to plate count data to calculate the time for a 4-log 10 decrease in population (T 4D). In all cases, survival increased with decreasing temperature. All acids inhibited S. flexneri to some extent: lactic > acetic > citric, malic, > tartaric acid. At 28 deg C, the T 4D values for the control medium and media containing acetic, citric, lactic, malic, and tartaric acids were 232, 145, 153, 120, 155, and 166 h, respectively. S. flexneri was undetectable (<1.32 log 10 CFU/ml) after 96 h at 28 deg C in BHI acidified to pH 4 with acetic or lactic acids, while the population remained unchanged in BHI acidified with HCl. Results suggest that organic acids may aid in inactivation of Shigella in foods. |
