Understanding the Effects of High Pressure on Bacterial Spores Using Synchrotron Infrared Spectroscopy

Abstract

Bacterial spores are extremely resistant life-forms that play an important role in food spoilage and foodborne disease. The return of spores to a vegetative cell state is a three-step process, these being activation, germination, and emergence. High-pressure (HP) processing is known to induce germination in part of the spore population and even to inactivate a high number of Bacillus spores when combined with other mild treatments such as the addition of nisin. The aim of the present work was to investigate the mechanisms involved in the sensitization of spores to nisin following HP treatment at ambient temperature or with moderate heating leading to a heterogeneous spore response. Bacillus subtilis spores were subjected to HP treatment at 500 MPa at 20 and 50 • C. The physiological state of different subpopulations was characterized. Then Fourier transform infrared (FTIR) microspectroscopy coupled to a synchrotron infrared source was used to explore the heterogeneity of the biochemical signatures of the spores after the same HP treatments. Our results confirm that HP at 50 • C induces the germination of a large proportion of the spore population. HP treatment at 20 • C generated a subpopulation of ungerminated spores reversibly sensitized to the presence of nisin in their growth medium. Regarding infrared spectra of individual spores, spores treated by HP at 50 • C and germinated spores had similar spectral signatures involving the same structural properties. However, after HP was performed at 20 • C, two groups of spores were distinguished; one of these groups was clearly identified as germinated spores. The second group displayed a unique spectral signature, with shifts in the spectral bands corresponding to changes in membrane fluidity. Besides, spores spectra in the amide region could be divided into several groups close to spectral properties of dormant, germinated, or inactivated spores. The part of the spectra corresponding to αhelix and β-sheet-structures contribute mainly to the spectral variation between spores treated by HP at 20 • C and other populations. These changes in the lipid and amide regions could be the signature of reversible changes linked to spore activation.

Antibacterial mechanism of ultrasound against Escherichia coli: Alterations in membrane microstructures and properties

“…Furthermore, Fourier transform infrared (FTIR) spectroscopy is known to be of a great value in characterizing the cell metabolism and biochemical properties of some cell membrane components, such as lipids, proteins, and nucleic acid, etc. [17] . Given all the functional groups of these organic molecules absorb infrared light specifically, the structural and physiological alterations on the bacterial cells upon different stress could be studied by FTIR analysis [18] .…”

“…Given all the functional groups of these organic molecules absorb infrared light specifically, the structural and physiological alterations on the bacterial cells upon different stress could be studied by FTIR analysis [18] . This technique has been applied to explore changes at cellular level of E. coli and Staphylococcus aureus upon plasma treatment [19] and the physiological state of Bacillus subtilis spores subjected to high pressure treatment [17] . However, to date, very few studies have reported the changes of cell membrane fluidity and potential under ultrasonic field.…”

Evaluation of the Physical Stability of Starch-Based Hydrogels Produced by High-Pressure Processing (HPP)

“…These results confirmed the well-known findings that HPP treatments cause sublethal injuries on certain resistant microorganisms that are able to repair cellular damages due to pressure and recover their viability during storage, as reported elsewhere [ 28 , 29 ]. In this regard, it can be hypothesized that the resistant survivors detected in corn, wheat, and tapioca-starch-based HPP hydrogels could belong to pressure-resistant microbial subpopulations such as bacterial spores [ 30 ], which seemingly differ based on the type of starch source and should be addressed in further experiments. Bacterial spores are extremely resistant life forms triggered by stress scenarios such as high-pressure conditions, returning to active growth during storage at optimal temperature conditions such as 20 °C [ 30 , 31 ].…”

Mechanisms and Applications of Bacterial Sporulation and Germination in the Intestine

“…This agent opens spores’ SpoVA channels for CaDPA, leading to rapid CaDPA release [ 84 ]. One final germinant is high hydrostatic pressure; pressures of 50–300 megaPascals trigger germination by directly activating IM GRs, while even higher pressures, 400–900 mPA, trigger the opening of the CaDPA channel in all spores that have been tested [ 85 , 86 ]. Dodecylamine, which is often used as a surfactant, and high pressure are not directly implicated in spore germination in the gut but are of importance in light of needs for spore eradication in hygiene and food processing.…”