Abstract
Electron-microscopic cytological observations ofBacillus stearothermophilus (FS 7954) spore death during moist heat exposure partially elucidated the physical behaviour of cells predicted by a previously suggested kinetic model of death. This model consisted of two consecutive reaction states prior to death and accounted for the nonlogarithmic behaviour. Morphology of spores during the early heat exposure, where the majority of spores are still viable, remain unchanged from the initial state. Some changes were recognized in the spore laminated inner-coat layer. There are indications that this layer consists of keratin fibrils. These fibrils contract upon heating. It is believed that this contraction causes, either directly or indirectly, some water to be expelled from the spore protoplast. This belief is supported by previous observation of a minimum in the free deuterium oxide content of the spore given similar heat exposure. It is suggested that this contraction is the reason for enhanced thermal resistance during the nonlogarthmic death process. On prolonged heating the integrity of the spore coat integuments and protoplast envelopes become lost. This is concomitant with the death of spores and onset of increase in free deuterium oxide content. These cytological observations, together with changes in free water content and the kinetic behaviour of the sequential model for the death process, are discussed from the viewpoint of cellular membrane stability.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Berlin E., Curran H. R., Pallansch M. M.: Physical surface features and chemical density of dry bacterial spores.J. Bacteriol.86, 1030 (1963).
Black S. H., Arredondo M. I.: Evidence for an intracellular membrane in core of spores ofBacillus popilliae.Experientia22, 77 (1966).
Bradley D. E., Franklin J. G.: Electron microscope survey of the surface configuration of spores of the genusBacillus.J. Bacteriol.76, 618 (1958).
Brannen J. P.: On the role of DNA in wet heat sterilization of microorganisms.J. Theoret. Biol.27, 425 (1970).
Brock T. D.: Life at high temperature.Science158, 1012 (1967).
Crewther W. G., Fraser D. R. B., Leunox H. F., Lindley H. F.: The chemistry of keratins.Adv. Protein Chemistry20, 191 (1965).
Deindoerfer F. H., Humphrey A. E.: Analytical methods for calculating heat sterilization times.Appl. Microbiol.7, 256 (1958).
Finean J. B.: The fibrous proteins, p. 117, InEngstrom-Finean Biological Ultrastructure, 2nd ed. Academic Press 1967.
Fox K., Eder B.: Comparison of survival curves ofBacillus subtilis spores subjected to wet and dry heat.J. Food Sci.34, 518 (1969).
Frasca J. M., Parks V. R.: A routine technique for double-staining ultrathin sections using uranyl and lead salts.J. Cell Biol.25, 157 (1965).
Frederickson A. G.: Stochastic models for sterilization.Biotechnol. Bioeng.8, 167 (1966).
Freer J. H., Levinson H. S.: Fine structure ofBacillus megaterium during microcycle sporogenesis.J. Bacteriol.94, 441 (1967).
Gerhardt P., Black S. H.: Permeability of bacterial spores, p. 218, in H. O. Halvorson (Ed.):Spores II, Burgess Publ. Co., Minn., USA, (1960).
Glanert A. M., Glanert R. H.: Araldide as an embedding medium for electron microscopy.J. Biophys. Biochem. Cytol.4, 191 (1958).
Hibagi Y., Iijima K., Kadota H.: Splitting line of bacterial spore.Nature215, 1392 (1967).
Hunnel J. W., Ordall Z. J.: Cytological and chemical changes in heat killed and germinated bacterial spores, p. 101, in H. O. Halvorson (Ed.):Spores II, Burgess Publ. Co., Minn., USA, 1960.
Kadota H., Iijima K., Uchida A.: The presence of keratinlike substance in spore coat ofBacillus subtilis.Agric. Biol. Chem.29, 870 (1965).
Kellenberger E., Ryter A., Séchaud J.: Electron microscope study of DNA-containing plasma. II. Vegetative and mature phage DNA as compared with normal bacterial nucleoids in different physiological states.J. Biophys. Biochem. Cytol.4, 671 (1958).
Keynan A., Issahary-Braud G., Evenchik Z.: Activation of bacterial spores, p. 180, in L. L. Campbell, H. O. Halvorson (Eds.):Spores III, American Society for Microbiology (1965).
Lewis J. C., Snell N. S., Burr H. K.: Water permeability of bacterial spores and the concepts of a contractile cortex.Science132, 544 (1960).
Murrell W. G.: The biochemistry of the bacterial endospore.Adv. Microbial. Physiol.1, 133 (1967).
Ohye D. F., Murrell W. G.: Formation and structure of the spore ofBacillus coagulans.J. Cell Biol.14, 111 (1962).
Prokop A., Humphrey A. E.: Kinetics of disinfection, p.61, in M. A. Benarde (Ed.):Disinfection, Marcell Dekker Inc., New York (1970).
Reynolds E.S.: The use of lead citrate at high pH as an electron-opaque stain in electron microscopy.J. Cell Biol.17, 208 (1963).
Rosemberg B., Remeny G., Switser R. C., Hamilton T. C.: Quantitative evidence for protein denaturation as the cause of thermal death.Nature232, 472 (1971).
Rousseau M., Fléchon J., Hermier J.: Etude an microscope électronique de la germination de la spore chezBacillus subtilis.Ann. Inst. Pasteur111, 149 (1966).
Sacks L. E., Thomas R. S.: Internal membraneous structure inBacillus macerans spores.S. Bacteriol.89, 1615 (1965).
Scharer J. M.:Ph. D. Thesis, University of Pennsylvania, USA (1965).
Stern J. A., Proctor B. E.: A micromethod and apparatus for the multiple determination of rates of destruction of bacteria and bacterial spores subjected to heat.Food Technol.7, 138 (1954).
Thomas R. S.: Ultrastructural localization of mineral matter in bacterial spores by microincineration.J. Cell. Biol.23, 113 (1964).
Tokuyasu K., Yamada E.: Fine structure ofBacillus subtilis II. Sporulation progress.J. Biophys. Biochem. Cytol.5, 129 (1959).
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
Prokop, A., Humphrey, A.E. Mechanism of thermal death of bacterial spores: Electron-microscopic observations. Folia Microbiol 17, 437–445 (1972). https://doi.org/10.1007/BF02872728
Received:
Issue Date:
DOI: https://doi.org/10.1007/BF02872728