Thermal Activation and Dry‐heat Inactivation of Spores of Bacillus subtilis MD2 and Bacillus subtilis var. niger

Abstract

Spores of Bacillus subtilis MD2 and Bacillus subtilis var. niger were heat activated for different times at 60° and 80°C. Strain MD2 required considerable heat activation while B. subtilis var. niger did not. Maximum germination rates increased with heat activation dose and declined subsequently without loss of germinability. Germination rates and percentages were considerably greater in tryptone glucose extract (TGE) than in nutrient broth. The addition of 2°° dimethyl sulphoxide did not increase germination in nutrient broth. The spores of var. niger are more resistant to dry‐heat than MD2 although they are less resistant to moist heat. Survivor curves in the dry‐heat range 140°‐170°C gave D‐values from 4–123 to 0.106 min for MD2 and 5.679 to 0.233 min for var. niger recovered on TGE agar. D‐values were lower on poorer media. The z‐values for MD2 and var. niger on TGE were 18.7°C and 21.25d̀C respectively.

Sensitization of thermally injured spores of Bacillus stearothermophilus to sodium benzoate and potassium sorbate

“…Evidence provided here demonstrates that zvalues calculated for this organism were not affected when potassium sorbate and sodium benzoate were added to the counting medium. From our data and the others available in the literature for B. stearothermophilus (Feeherry et al 1987;López et al 1997) and other spore-formers (Gurney and Quesnel 1980;González et al 1995González et al , 1996González et al , 1997 …”

Importance of Considering Injured Microorganisms in Sterilization Validation

“…For example, Ca, glucose or alanine are considered as germinants and thus inclusion of them into the culture medium is indispensable to attain reproducible and successful sterilization validation (Shintani, 2006;Sasaki et al, 2000). Damage to the germination system has been demonstrated with the use of calcium dipicolinate (Edwards et al, 1965a,b), lactate (Foegeding and Busta, 1983a), lysozyme Adams and Busta, 1972;Barach et al, 1974;Adams, 1974;Duncan et al, 1972;Alderton et al, 1974), and mixtures of amino acids (Uchida and Kadota, 1979;Gurney and Quesnel, 1981;Gurney and Quesnel, 1980) and so on. As most chemicals that promote improved recovery (e.g., lysozyme, other lytic enzymes, calcium dipicolinate, and amino acids) are involved in promoting spore germination (Gould, 1984), it is speculated that they act by helping the spores bypass the injured L-alanine germination system (Gould, 1984).…”

“…The inactivation of germination enzymes has been supported by large losses of cortex lytic enzyme activity in thermally injured spores, and by thermodynamic values for the inactivation of the L-alanine germination system that were consistent with protein denaturation . Increased recovery by the use of complex amino acid mixtures may be effective through the generation of NADH and ammonium, since these could be unavailable in the Lalanine germination system through the inactivation cycle (Gurney and Quesnel, 1981;Gurney and Quesnel, 1980). Treatment with chemical agents may render the germination process sensitive to lysozyme, which enhances the germination of spores (Hurst, 1977).…”

The Reduction of Aerobic Bacterial Counts of Bovine Milk as Influenced by Heat-treatments at Pasteurisation Temperatures

“…The occurrence of spore forming strain also possibly influenced such a variation. Those spores germinated at pasteurisation temperature so that they were observed during bacterial enumeration [20][21][22][23][24][25][26][27]. …”