title: Differential scanning calorimetry of bacteria.
abstract: Thermograms obtained by differential scanning calorimetry of a range of bacteria of different heat resistances were compared. Equations were derived to calculate the rate at which the numbers of viable organisms in a calorimeter decline as the temperature is raised at a constant rate. Vegetative bacteria scanned at 10 degrees C min-1 showed multi-peaked thermograms with four major peaks (denoted m, n, p and q) occurring in the regions 68-73, 77-84, 89-99 and 105-110 degrees C respectively. Exceptions were that peak m (the largest peak) occurred at 79-82 degrees C in Bacillus stearothermophilus and an additional peak, r, was detected in Escherichia coli at 119 degrees C. At temperatures below the main peak m there were major differences in thermograms between species. There was a direct relationship between the onset of thermal denaturation and the thermoresistance of different organisms. Heat-sensitive organisms displayed thermogram features which were absent in the more heat-resistant types. When samples were cooled to 5 degrees C and re-heated, a small endothermic peak, pr, was observed at the same temperature as p. Peaks p and pr were identified as the melting endotherms of DNA. In all vegetative organisms examined, maximum death rates, computed from published D and z values, occurred at temperatures above the onset of thermal denaturation, i.e. cell death and irreversible denaturation of cell components occurred within the same temperature range.
mesh_terms: D001409:Bacillus cereus / Q000032:analysis; D001419:Bacteria / Q000032:analysis*; D001482:Base Composition; D002151:Calorimetry; D002152:Calorimetry, Differential Scanning; D004269:DNA, Bacterial; D013293:Enterococcus faecalis / Q000032:analysis; D004926:Escherichia coli / Q000032:analysis; D001411:Geobacillus stearothermophilus / Q000032:analysis; D011549:Pseudomonas / Q000032:analysis; D013291:Streptococcus / Q000032:analysis; D013696:Temperature; D014733:Vibrio / Q000032:analysis
chemical_list: D004269:DNA, Bacterial