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

Abstract

The effects of post‐treatment environmental factors on the heat resistance of Bacillus stearothermophilus spores (ATCC 12980, 7953, 15951 and 15952) were investigated. Nutrient Agar (NA), Antibiotic Assay Medium (AAM), Dextrose Tryptone Agar (DTA) and Tryptic Soy Agar (TSA) with Ca2+ added to a final concentration of 100 p.p.m. were used as recovery media. No significant differences were seen between D‐values obtained except in the case of strain 12980 when comparing TSA with the other media and for strain 7953 comparing AAM and DTA. The optimum incubation temperature was slightly lower for heated than for unheated spores of each strain, although, in general, 50 °C was adequate. Higher D‐values were obtained at 50–55 °C. The effects of the pH of the medium in the range 5.0–7.0 and the addition of starch and phosphate on heat resistance have also been investigated. Maximum colony counts of heated spores were obtained at pH 7.0 and decreased as pH fell. D‐values were significantly lower at pH ≤ 5.5. Increasing the concentration of phosphate in the recovery medium from 0 to 0.2% resulted in a progressive decrease in spore recovery and D‐values. The addition of starch improved recoverability. The z‐values obtained for the four strains studied under the different recovery conditions were similar with a mean value of 7.58 °C ± 0.28.

Inactivation ofGeobacillus stearothermophilusSpores by High-Pressure CarbonDioxideTreatment

“…Previous studies have shown that G. stearothermophilus spores are highly resistant to heat (7,20,26). Similarly, we found that at 85°C the heat treatment D value for G. stearothermophilus spores was remarkably higher than the values for four other species.…”

“…G. stearothermophilus usually causes flat sour spoilage of canned liquid foods, such as coffee, during storage in automatic vending machines. Because of the heat resistance of this microorganism's spores, they are often used as a biological indicator to evaluate the effectiveness of sterilization processes (7,20,26). In general, foods are cooked at temperatures around 100°C, and it is assumed that the foods are not damaged by heat treatment at temperatures below 100°C.…”

Characterization of Bacillus cereus spores isolated from Algerian processed cheese

“…At 102°C D value (D102°C) for the strain studied LMBCF002 decreased from 4.30 to 0.95min; for pH=7 and pH=4.5 respectively. The result suits those quoted by Lopez et al (1997) and Couvert (1999). The obtained ZpH=3.58 value was close to ZpH reported by Gaillard et al (1998).…”

Inactivation of Geobacillus stearothermophilus spores by alkaline hydrolysis applied to medical waste treatment

“…The D-values herein obtained at 100 o C were even lower than those found in studies using thermal inactivation at temperatures above 100 o C. Except in the experiments carried out with 0.1 M NaOH, the highest D-value obtained was 2.3 min (Table 1). In contrast, at 120 o C, Lo 'pez et al (1997) reported D-values ranging from 1.32 to 2.84 min, while at 121 o C, Feeherry et al (1987) and Guizelini et al (2012) reported D-values from 1.3 to 5.4 min. Nevertheless, the time required to complete inactivation of G. stearothermophilus spores in the present study was probably, different from those obtained in abovementioned studies.…”

“…Indeed, the low water content in the core and the intrinsic thermostability of proteins confers to spores of thermophilic species a higher resistant to wet heat than to those of mesophiles (Guizelini et al, 2012). Therefore, the spores of this organism are often used as a biological indicator to assess the effectiveness of sterilization methods (Lo 'pez et al, 1997;Watanabe et al, 2003;Wood et al, 2010).…”