ACID ADAPTATION SENSITIZES SALMONELLA-TYPHIMURIUM TO HYPOCHLOROUS ACID

Acid adaptation of Salmonella typhimurium at a pH of 5.0 to 5.8 for on e to two cell doublings resulted in marked sensitization of the pathog en to halogen-based sanitizers including chlorine (hypochlorous acid) and iodine, Acid-adapted S. typhimurium was more resistant to an anion ic acid sanitizer than was its nonadapted counterpart, A nonselective plating medium of tryptose phosphate agar plus 1% pyruvate was used th roughout the study to help recover chemically stressed cells, Mechanis ms of HOCl-mediated inactivation of acid-adapted and nonadapted salmon ellae were investigated, Hypochlorous acid oxidized a higher percentag e of cell surface sulfhydryl groups in acid-adapted cells than in nona dapted cells, and sulfhydryl oxidation was correlated with cell inacti vation, HOCl caused severe metabolic disruptions in acid-adapted and n onadapted S. typhimurium, such as respiratory loss and inability to re store the adenylate energy charge from a nutrient-starved state, Sensi tization of S. typhimurium to hypochlorous acid by acid adaptation als o involved increased permeability of the cell surface because nonadapt ed cells treated with EDTA became sensitized, The results of this stud y establish that acid adapted S. typhimurium cells are highly sensitiz ed 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 Sal monella and implies that acid pretreatment of food plant environments may increase the efficacy of halogen sanitizers.