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Appl. Environ. Microbiol., Feb 1997, 461-467, Vol 63, No. 2
GJ Leyer and EA Johnson
Acid adaptation of Salmonella typhimurium at a pH of 5.0 to 5.8 for one to
two cell doublings resulted in marked sensitization of the pathogen to
halogen-based sanitizers including chlorine (hypochlorous acid) and iodine.
Acid-adapted S. typhimurium was more resistant to an anionic acid sanitizer
than was its nonadapted counterpart. A nonselective plating medium of
tryptose phosphate agar plus 1% pyruvate was used throughout the study to
help recover chemically stressed cells. Mechanisms of HOCl-mediated
inactivation of acid-adapted and nonadapted salmonellae were investigated.
Hypochlorous acid oxidized a higher percentage of cell surface sulfhydryl
groups in acid-adapted cells than in nonadapted cells, and sulfhydryl
oxidation was correlated with cell inactivation. HOCl caused severe
metabolic disruptions in acid-adapted and nonadapted S. typhimurium, such
as respiratory loss and inability to restore the adenylate energy charge
from a nutrient-starved state. Sensitization of S. typhimurium to
hypochlorous acid by acid adaptation also involved increased permeability
of the cell surface because nonadapted cells treated with EDTA became
sensitized. The results of this study establish that acid-adapted S.
typhimurium cells are highly sensitized to HOCl oxidation and that
inactivation by HOCl involves changes in membrane permeability, inability
to maintain or restore energy charge, and probably oxidation of essential
cellular components. This study provides a basis for improved practical
technologies to inactivate Salmonella and implies that acid pretreatment of
food plant environments may increase the efficacy of halogen sanitizers.
Copyright © 1997, American Society for Microbiology
Acid adaptation sensitizes Salmonella typhimurium to hypochlorous acid
Department of Food Microbiology and Toxicology, University of Wisconsin, Madison 53706, USA.
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