Thermal inactivation and injury of Bacillus stearothermophilus spores

Abstract

Aqueous spore suspensions of Bacillus stearothermophilus ATCC 12980 were heated at different temperatures for various time intervals in a resistometer, spread plated on antibiotic assay medium supplemented with 0.1% soluble starch without (AAMS) or with (AAMS-S) 0.9% NaCl, and incubated at 55°C unless otherwise indicated. Uninjured spores formed colonies on AAMS and AAMS-S; injured spores formed colonies only on AAMS. Values of D, the decimal reduction time (time required at a given temperature for destruction of 90% of the cells), when survivors were recovered on AAMS were 62.

Influence of recovery conditions on apparent heat resistance of Bacillus stearothermophilus spores

“…In relation to the effect of the subculture temperature our results show that the most suitable procedure for spore recovery after heating treatment is the use of slightly lower temperatures than the optimum for the growth of unheated spores. This agrees with previous results of Cook & Gilbert (1968) and Feeherry et al (1987), although it differs from those obtained by Mallidis & Scholefield (1986) who found better B. stearothermophilus spore counts at 60 ЊC than at 50 ЊC. Our results also show that D-values were only affected by recovering at 40 ЊC.…”

“…However, as this research was carried out at pH levels close to neutral, it is difficult to say how this quantitatively affects resistance of the organism in medium acid canned foods. Despite the great importance that the temperature of subculturing has on the apparent heat resistance, little attention has been given to the influence of incubation temperature on thermal characteristics of B. stearothermophilus and conflicting results have been reported (Cook & Gilbert, 1968;Mallidis & Scholefield, 1986;Feeherry et al, 1987).…”

Factors Influencing Recovery of Heat‐injured Bacillus thuringiensis Spores. Statistical Approach

“…However, the effect of the recovery temperature on B. cereus varied considerably depending on the strain. Nevertheless, fewer B. stearothermophilus spores were repaired at lower temperatures, even after a prolonged incubation period of 14 days (Feeherry et al, 1987). Of the surviving fraction, 62% which were able to proliferate at 55ЊC were unable to grow at 40ЊC.…”

“…In contrast, membrane damage may explain the increased sensitivity of heat-stressed sores to selective components such as antibiotics, curing salts or pH indicators such as bromocresol purple (Foegeding and Busta, 1981). This widespread result has often been demonstrated as a NaCl effect with B. stearothermophilus (Brown and Gaze, 1988;Feeherry et al, 1987;Labbe, 1979), B. subtilis, B. pumilus (Briggs andYazdany, 1970) and B. cereus (Adams, 1978). This increase in NaCl sensitivity has been used as an index of the percentage of injured spores.…”

Multiplex PCR for rapid detection of thermophilic Moorella thermoaceticaand Geobacillus stearothermophilus from canned foods and beverages

“…are often found in canned products. All of these species produce highly heat-resistant endospores (Ashton, 1981;Feeherry et al, 1987;Byrer et al, 2000) and share high heatresistance profiles. For example, G. stearothermophilus has a decimal reduction time at 121°C of >1 min in most instances, with M. thermoacetica displaying a thermal reduction time of ≥1 h at 124°C (Byrer et al, 2000;Sasaki et al, 2000), depending on sporulation conditions.…”