Influence of Sublethal Treatment with Heat or Chlorine on the Growth of Psychrophilic Bacteria

Abstract

When cultures of psychrophilic bacteria isolated from milk were partially killed by heat, the survivors had a greatly increased lag phase when holding was at 5 or 10[degree] C. A slightly increased lag phase was noted when holding was at 25[degree]C. Immediately after heating, larger numbers of survivors of sublethal doses of heat failed to develop colonies on Standard Plate Count agar than on Tryptone, glucose-meat extract agar, but by 24 hours this difference had largely disappeared. The growth curves of organisms surviving treatment with chlorine were not altered to any great extent.