Analysis of Bacillus cereus cell viability, sublethal injury, and death induced by mild thermal treatment

Abstract

As the most cost‐effective tool to ensure microbial safety, thermal processing induces a large portion of sublethal injury presenting a potential hazard to food safety. Thermal treatment at 63 °C for 1 min injured 2.22 log cfu/ml totally, half of which were sublethally injured using plate counting method. After 2 min, the inactivation log of Bacillus cereus reached 1.55 while the sublethally injured log even reached 2.16. As for the sublethally injured rate of the B. cereus, it was over 65% after 0.5 min and kept ever‐increase with time. In the end, the injured rate arrived at 99.30% after 2 min processing time. Partial esterase enzyme inactivation was found after 0.5 min heat treatment with flow cytometry combining carboxyfluorescein diacetate/propidium iodide (PI) double‐staining, but B. cereus was not dyed by PI at 63 °C. Comparing with the initial protein concentration of 0.57 ± 0.02 μg/ml, the leakage of the protein was not so notable though the general trend was increasing with duration of heat. Scanning and transmission electron microscopy analysis revealed that a portion of cells morphology and structure had changed after thermal process. Practical applications Bacillus cereus is an endospore forming pathogenic, causing foodborne illnesses and outbreaks all over the world. This research indicated that thermal treatment at 63 °C was a sublethal stress for B. cereus that a portion of cells were sublethally injured which could resume growth in suitable condition and might exist potential safety hazard if used for food pasteurization.

Flow Cytometry Combined With Single Cell Sorting to Study Heterogeneous Germination of Bacillus Spores Under High Pressure

“…Based on our findings, we suggest renaming sub-populations with high and intermediate SYTO16 intensities as "germinated with high physiological fitness" and "germinated with partial sublethal damage, " respectively. For future research, it would be of interest to study this potential sub-lethal damage in greater detail, e.g., by looking for decreased plating efficiencies in unfavorable conditions (Ray, 1979;Somolinos et al, 2008;Schottroff et al, 2018;Lv et al, 2019). Further, it would be of interest to get a better understanding of the structural nature of this sublethal damage.…”

Functional metagenomic analysis of dust-associated microbiomes above the Red Sea

“…We provide here the first attempt at describing the Red Sea Aeolian microbiome from a functional metagenomics perspective, and reviewed the literature on the functions postulated to be important in supporting successful Aeolian microbial transport to propose a set of targeted genes that help define the Aeolian lifestyle. As a consequence, a set of functions was selected to be analyzed in the airborne metagenomes, these functions are aerosolization 13 , allowing microbes to be entrained from surfaces (soils, plants or water) to the air facilitated by gas vesicles inside the cells, aerotaxis 14 and chemotaxis 15 , which are the movement of microbes under the influence of oxygen or chemical gradient that allow them to be positioned at the surface of their habitat, UV radiation 16 and heat resistance 17 , which function in repairing the DNA damages induced by UV radiation and thermal stresses, germination 18 and sporulation 19 , where the cells can form spores, which allow them to survive desiccation and exposure to UV radiation and germinate under harsh conditions, and biofilm formation 20 that enable the microorganisms to attach to surfaces such as dust particles. We propose here this set of functions as a parsimonious set of traits that delineates capacities that, in combination, allow biological particles to survive atmospheric transport.…”

Probiotic dried apple snacks: Development of probiotic coating and shelf‐life studies

“…This reduction may be related to the death of injured spores of B. coagulans that are rapidly deactivated during storage. Drying processes may injure part of the microbial cells and spores as has been reported for several microorganisms, such as Lactococcus lactis (Wang et al, 2020), Bacillus cereus (Lv et al, 2019), and Bacillus amyloliquefaciens (Dong et al, 2015).…”