Bacterial Spores I. A Study in Heat Resistance and Dormancy

Abstract

Our knowledge regarding the properties of bacterial spores, per se, has been impeded by the more or less universal impression that spores are metabolically inactive or inert. Except for occasional theories concerning spore-cycles and the like, the usual conception of spore function has been limited to ipso facto sporulation under conditions of unfavorable environment, and germination when conditions again become favorable. Some exceptions are noted in the cases of certain organisms having peculiar tendencies toward dormancy or latent germination.Spore properties, such as minimal metabolism, respiration, enzyme production and the possibility of varying degrees of pregermination stimulation have received little attention or credence. There have been isolated attempts to gain information concerning these still hypothetical properties; some of these will be discussed later.Just as studies of the intimate details of metabolism have aided greatly in other fields of biological research, so a finer comprehension of spore properties and spore function should result in material improvement and greater precision in studies of the heat resistance and dormancy of bacterial spores, a subject which so vitally affects various routine laboratory procedures and their industrial applications.The two strains of the organism with which all of the preliminary work reported here was concerned were isolated in pure cul-1 This communication is based on a portion of a thesis submitted to the Graduate School of Yale University by the senior author in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

The accelerating effect of sublethal heat on spore germination in mesophilic aerobic bacteria

“…The results obtained with the different heating mediums are of interest in connection with an earlier observation by Morrison and Rettger (1930a). These authors found that the spores of a spoilage organism when heated in water and subcultured in broth exhibited the familiar "skips" with a consequent ill-defined thermal death-time.…”

The Nonlogarithmic Rate of Thermal Destruction of Spores of Bacillus coagulans12

“…This view is consistent with the concept that death of a particular cell is a chance event, and that all cells have the same probability of destruction at any given instant during heating. Attempts have been made to demonstrate the presence of organisms of differing resistances in a given population, and the results have been variable (Magoon 1926;Williams, 1929;Sommer, 1930;Morrison and Rettger, 1930;Davis and Williams, 1948;Sugiyama, 1951;and Desrosier and Esselen, 1951). Yesair and Cameron (1936) reported that by differential centrifugation they were able to separate a spore crop of a putrefactive anaerobe into fractions of differing thermal resistances.…”

Relation of Maximum Growth Temperature to Resistance to Heat

“…Esty and Cathcart (1921) have shown that heating in soft or hard glass changes the pH of a solution. The buffer has been reported by Morrison and Rettger (1930) to resist change in pH at the temperatures and times employed.…”