Summary: The effect of NaCl on the thermal inactivation of Listeria monocytogenes has been investigated by conventional microbiological techniques and by using differential scanning calorimetry (DSC). Addition of 1·5 m-NaCI to cells grown at lower NaCl concentrations significantly increases the tolerance of cells to mild heat stress (56–62 °C). DSC thermograms show five main peaks which are shifted to higher temperatures in the presence of 1·5 m-NaCI. Measurement of loss of viability in the calorimeter gave good correlation between cell death and the first major thermogram peak at two NaCI concentrations. The time course of the loss of this first peak when cells were heated and held at 60 °C in the calorimeter matched the loss of viability, whereas the peak attributable to DNA showed little change during this process. The use of DSC to investigate the mechanisms involved in thermal inactivation is discussed.
BunningV. K.,
DonnellyC. W.,
PeelerJ. T.,
BriggsE. H.,
BradshawJ. G.,
CrawfordR. G.,
BeliveauC. M.,
TierneyJ. T.1988; Thermal inactivation of Listeria monocytogenes within bovine milk phagocytes. Applied and Environmental Microbiology 54:364–370
ColeM. B.,
JonesM. V.1990; A submerged-coil heating apparatus for investigating the thermal inactivation of bacteria. Letters in Applied Microbiology II:233 235:
ConnorD. E.,
BrackettR. E.,
BeuchatL. R.1986; Effect of temperature, NaCl and pH on growth of Listeria monocytogenes in cabbage juice. Applied and Environmental Microbiology 52:59–63
CooteP. J.,
HolyoakC. D.,
ColeM. B.1991; Thermal inactivation of Listeria monocytogenes during simulated microwave heating. Journal of Applied Bacteriology (in the Press)
CrabbJ. W.,
MurdockA. L.,
AmelunxenR. E.1975; A proposed mechanism of thermophily in facultative thermophiles.. Biochemical and Biophysical Research Communications 62:627–633
GazeJ. E.,
BrownG. D.,
GaskellD. E.,
BanksJ. G.1989; Heat resistance of Listeria monocytogenes in homogenates of chicken, beef steak and carrot. Food Microbiology 6:251–259
GoepfertJ. M.,
IskanderI. K.,
AmundsonC. H.1970; Relation of the heat resistance of Salmonellae to the aw of the environment.. Applied Microbiology 19:429–433
GriemeL. E.,
BarbanoD. M.1983; Method for use of a differential scanning calorimeter for determination of bacterial thermal death times. Journal of Food Protection 46:797–801
HurstA.,
HughesA.1981; Repair of salt tolerance and recovery of lost D-alanine and magnesium following sublethal heating of Staphylococcus aureus are independant events. Canadian Journal of Microbiology 27:627–632
JonesM. V.,
SpencerW. N.1985; Thermostability of the enzymes of the tricarboxylic acid cycle of Bacillus coagulans . Antonie van Leeuwenhoek 51:193–201
LambertP. A.,
HammondS. M.1973; Potassium fluxes, first indication of membrane damage in microorganisms. Biochemical and Biophysical Research Communications 54:796–799
LeeA. C.,
GoepfertJ. M.1975; Influence of selected solutes on thermally induced death and injury of Salmonella typhimurium . Journal of Milk and Food Technology 38:175–200
LepockJ. R.,
FreyH. E.,
RodahlM.,
KruuvJ.1988; Thermal analysis of CHL V79 cells using differential scanning calorimetry: implications for hyperthermic cell killing and heat shock response. Journal of Cellular Physiology 137:14–24
MackeyB. M.,
ParsonsS. E.,
MilesC. A.,
OwenR. J.1988; The relationship between base composition of bacterial DNA and its intracellular melting temperature as determined by differential scanning calorimetry. Journal of General Microbiology 134:1185–1195
NollerH. F.,
NomuraM.1987; Ribosomes. Escherichia coli and Salmonella typhimurium: Cellular and Molecular Biology104–125NeidhardtF. C.,
IngrahamJ. L.,
LowK. B.,
MagasanikB.,
SchaechterM.,
UmbargerH. E.
Washington, DC: American Society for Microbiology;
PrivalovP. L.,
KnechninashviliN. N.1974; A thermodynamic approach to the stabilization of globular protein structure: a calorimetric study. Journal of Molecular Biology 86:665–654
RheinbergerH.,
GeigenmullerU.,
WeddeM.,
NeirhausK. H.1988; Parameters for preparation of E. coli ribosomes and ribosomal sub-units active in tRNA binding. Methods in Enzymology 164:658–662
VerripsC. T.,
KwastR. H.1977; Heat resistance of Citrobacter freundii in media with various water activities. European Journal of Applied Microbiology 4:225–231