Effects of spore purity on the wet heat resistance of Clostridium perfringens, Bacillus cereus and Bacillus subtilis spores

Authors: Juneja, Vijay; Osoria, Marangeli; ALTUNTAS, EVRIM - Ankara University; TANEJA, NEETU - National Institute Of Food Technology Entrepreneurship And Management(NIFTEM); THAKUR, SHEETAL - Chandigarh University; KUMAR, GOVINDARAJ - University Of Georgia; SETLOW, PETER - University Of Connecticut

Submitted to: Food Research International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2023
Publication Date: 12/22/2023
Citation: Juneja, V.K., Osoria, M., Altuntas, E.G., Taneja, N.K., Thakur, S., Kumar, G.D., Setlow, P. 2023. Effects of spore purity on the wet heat resistance of Clostridium perfringens, Bacillus cereus and Bacillus subtilis spores. Food Research International. https://doi.org/10.1016/j.foodres.2023.113904.
DOI: https://doi.org/10.1016/j.foodres.2023.113904

Interpretive Summary: Clostridium perfringens, Bacillus cereus, and Bacillus subtilis are ubiquitous in the environment and thus, humans and our foodstuffs are continually in contact with these bacterial spores. Given the strong possibility that spore purity is potentially a variable that can affect spore wet heat resistance, the current work was undertaken to examine the wet heat resistance of spores purified to different degrees - with water washes alone, water washes followed by sonication, and with Histodenz centrifugation following sonication. We found that Histodenz centrifugation step is most important in rendering the spores more sensitive to the lethal effect of heat. These new insights into the heat resistance of bacterial spores should provide useful information to companies in making decisions on precise conditions to be used in the processing of thermally processed foods.

Technical Abstract: Heat resistance of spores of Clostridium perfringens 8238 (Hobbs Serotype 2), Bacillus cereus NCTC 11143 (4810/72), and Bacillus subtilis PS533, an isogenic derivative of strain PS832 (a 168 strain) was determined in ground beef at 95C. Spore purification was by centrifugation and washing with sterile distilled water (dH2O), followed by sonication and then Histodenz centrifugation for B. subtilis and C. perfringens, and centrifugation and washing with sterile dH2O followed by Histodenz centrifugation for B. cereus. Bags containing inoculated beef samples were submerged in a temperature-controlled water bath and held at 95C for predetermined lengths of time. Surviving spore populations were enumerated by plating on mannitol egg yolk polymyxin agar (MYP) agar plates for B. cereus and B. subtilis, and on tryptose-sulfite-cycloserine agar (TSC) agar plates for C. perfringens. Survivor curves were fitted to linear, linear with tail, and Weibull models using the USDA Integrated Pathogen Modeling Program (IPMP) 2013 software. The Weibull model provided a relatively better fit to the data since the root mean square error (RMSE), mean square error (MSE), sum of squared errors (SSE), and Akaike information criterion (AIC) values were lower than the values obtained using the linear or the linear with tail model. Additionally, the Weibull model accurately predicted the observed D-values at 95 °C for the three spore-formers since the accuracy factor (Af) values ranged from 1.03 to 1.08 and the bias factor (Bf) values were either 1.00 or 1.01. Times at 95C to achieve a 3-log reduction decreased from 206 min for C. perfringens spores purified with water washes alone to 191 min with water washes followed by sonication and Histodenz centrifugation, from 7.9 min for B. cereus spores purified with water washes alone to 1.4 min with water washes followed by Histodenz centrifugation, and from 20.6 min for B. subtilis spores purified with water washes alone to 6.7 min for water washes followed by sonication and Histodenz centrifugation. Thermal-death-time values reported in this study will assist food processors to design thermal processes to guard against bacterial spores in cooked foods. Spore purity is an additional factor in spore wet heat resistance, although the cause of this effect is not clear.