Difference in Injury of Cells of Vibrio parahaemolyticus Produced by Heat and Cold Stresses in liquid and Solid Menstrual

Abstract
Cells of Vibrio parahaemolyticus were stressed by heat, cold or heat-cold treatments of 45 C for 12 h, 0 C for 24 h or both. The five menstrua in which cells were stressed were 0.1 M phosphate buffer with 3% NaCl (B + 3%), 0.25 - strength Marine Broth (0.25 × MB) Trypticase Soy Broth with 3% NaCl (TSB + 3%) and Trypticase Soy Agar with 3 or 7% NaCl (TSA + 3% or TSA + 7%). The chill stress produced no cell injury, measured as the difference in colony counts in TSA+3% and TSA+7%, in the three liquid menstrua but caused more than 4 logs of cell injury in the solid menstrua compared to controls. The heat stress caused 2.5- and 1.5-log increases in the number of injured cells from B + 3% or 0.25 × MB, respectively. Cells heat-stressed in TSB + 3% showed no decline in colony counts, but those heat-stressed in TSA+ 7% produced about a 6-log lower colony count. For cells heated and then chilled in B+3% or 0.25 × MB as the liquid menstruum, the percentages of heat-injured cells that apparently regained tolerance to 7% NaCl when shifted to the cold were about 99.7 and 95.0%, respectively. Conversely, cells that were heated and then chilled in the solid menstrua did not regain tolerance to 7% NaCl. Thus, cell injury was greater and apparently less easily reversed for cells stressed in solid than liquid menstrua.

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