Sublethal Injury and Viable but Non-culturable (VBNC) State in Microorganisms During Preservation of Food and Biological Materials by Non-thermal Processes

Abstract

The viable but non-culturable (VBNC) state, as well as sublethal injury of microorganisms pose a distinct threat to food safety, as the use of traditional, culture-based microbiological analyses might lead to an underestimation or a misinterpretation of the product’s microbial status and recovery phenomena of microorganisms may occur. For thermal treatments, a large amount of data and experience is available and processes are designed accordingly. In case of innovative inactivation treatments, however, there are still several open points with relevance for the investigation of inactivation mechanisms as well as for the application and validation of the preservation processes. Thus, this paper presents a comprehensive compilation of non-thermal preservation technologies, i.e., high hydrostatic pressure (HHP), pulsed electric fields (PEFs), pulsed light (PL), and ultraviolet (UV) radiation, as well as cold plasma (CP) treatments. The basic technological principles and the cellular and molecular mechanisms of action are described. Based on this, appropriate analytical methods are outlined, i.e., direct viable count, staining, and molecular biological methods, in order to enable the differentiation between viable and dead cells, as well as the possible occurrence of an intermediate state. Finally, further research needs are outlined.

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.…”

600-ns pulsed electric fields affect inactivation and antibiotic susceptibilities of Escherichia coli and Lactobacillus acidophilus

“…Although nsPEF technology is largely considered to be E-field driven, during treatment there is an energydependent increase in process temperature due to electric current flow and individual product resistance (Schottroff et al 2018); thus, additional inactivation effects due to heating should be considered. Consequently, for temperature-sensitive applications, it was important to differentiate inactivation triggered by the E-field from the thermal gradient.…”

Methods for detection of viable foodborne pathogens: current state-of-art and future prospects

“…For practicality in food microbiology, viability is commonly understood to mean the ability of bacterial cells to replicate in liquid culture media or to produce a visible colony on solid culture media (Davey 2011). Formation of colonies on a growth medium clearly demonstrates that at least one cell was able to replicate; thus, the cells are alive (Bogosian and Bourneuf 2001;Schottroff et al 2018). However, the delineation between life and death is a very complex concept, as the route from life to death can include different stages (Davey 2011;Schottroff et al 2018).…”

“…Formation of colonies on a growth medium clearly demonstrates that at least one cell was able to replicate; thus, the cells are alive (Bogosian and Bourneuf 2001;Schottroff et al 2018). However, the delineation between life and death is a very complex concept, as the route from life to death can include different stages (Davey 2011;Schottroff et al 2018). Microorganisms in foods exposed to stresses or different environmental conditions can exist in various metabolic states or growth phases and, in some of these states, might transiently lose the ability to grow on or in laboratory culture media.…”