Characterization of the acid tolerance response in Salmonella typhimurium and its impact on food safety.

摘要

Salmonella typhimurium can adapt to mild acid stress which enhances survival in severe acid environments. Acid-adapted cells had increased resistance to inactivation by organic acids commonly present in foods. They also had increased survival during a milk fermentation and in Cheddar, Swiss, and Mozzarella cheeses. Acid adaptation is an important survival mechanism enabling Salmonella spp. to persist in fermented dairy products and probably other acidic food products.;A variety of factors including organic acids, a;Although acid-adapted cells were more tolerant towards an acid anionic sanitizer, they were found unexpectedly to be markedly more susceptible to halogen based sanitizers. Hypochlorous acid (HOCl) oxidized a higher percentage of cell surface sulfhydryl groups in acid-adapted cells than in nonadapted cells. Other metabolic alterations in acid-adapted cells included respiration loss, enzyme inactivation, and an inability to restore the adenylate energy charge from a nutrient starved state. Permeabilization of the outer membrane by the use of a divalent cation chelator (EDTA), sensitized nonadapted cells towards HOCl. These results are discussed in relation to changes in membrane permeability that result in an accumulation of metabolic disruptions in S. typhimurium leading to cell death.;In summary, acid adaptation is an important stress response in Salmonella that has considerable implications in food, medical, and environmental microbiology. This adaptive condition should be considered when evaluating food systems and biocides in challenge tests for survival of foodborne pathogens.