Characterization of the Repair of Injury Induced by Freezing Salmonella anatum

Abstract

Fast freezing and slow thawing of Salmonella anatum cells suspended in water resulted in injury of more than 90% of the cells that survived the treatment. The injured cells failed to form colonies on the selective medium (xyloselysine-peptone-agar with 0.2% sodium deoxycholate) but did form colonies on a nonselective (xylose-lysine-peptone-agar) plating medium. In Tryptic soy plus 0.3% yeast extract broth or minimal broth, most of the injured cells repaired within 1 to 2 hr at 25 C. Tryptic soy plus yeast extract broth supported repair to a greater extent than minimal broth. Phosphate or citrate at concentrations found in minimal broth supported repair of some cells. MgSO 4 , when present with inorganic phosphate or citrate or both, increased the extent of repair. The repair process in the presence of phosphate was not prevented by actinomycin D, chloramphenicol, and D-cycloserine, but was prevented by cyanide and 2,4-dinitrophenol (only at p H 6). This suggested that the repair process might involve energy metabolism in the form of adenosine triphosphate. The freeze-injured cells were highly sensitive to lysozyme, whereas unfrozen fresh cells were not. In the presence of phosphate or minimal broth this sensitivity was greatly reduced. This suggested that, at least in some of the cells, the injury involved the lipopolysaccharide of the cell wall and adenosine triphosphate synthesis was required for repair.

Phosphate Buffer Increases Recovery of Escherichia coli O157:H7 from Frozen Apple Juice

“…Although these diluents may be appropriate for some foods, they may not be useful for recovering injured E. coli O157:H7 from acidic foods such as apple juice. Low concentrations of potassium phosphate (0.25%) have been shown to improve the recovery of freeze-injured Salmonella (27). Phosphate buffer (0.1 M) with or without 0.1% Tween 80 has been used as a diluent for recovering yeasts and molds from frozen fruit or fruit purees (3,5).…”

“…Cellular damage occurs during freezing, frozen storage, and thawing (4,11,17,22,29,32). Frozen and thawed microorganisms often exhibit increased sensitivity to selective ingredients found in media (27,28,38) and may display altered nutrient requirements (24,28). Organisms damaged by freezing and thawing may also exhibit an increased sensitivity to some peptones added to plating media (24).…”