Discrimination of Stressed and Non-Stressed Food-Related Bacteria Using Raman-Microspectroscopy

Abstract

As the identification of microorganisms becomes more significant in industry, so does the utilization of microspectroscopy and the development of effective chemometric models for data analysis and classification. Since only microorganisms cultivated under laboratory conditions can be identified, but they are exposed to a variety of stress factors, such as temperature differences, there is a demand for a method that can take these stress factors and the associated reactions of the bacteria into account. Therefore, bacterial stress reactions to lifetime conditions (regular treatment, 25 °C, HCl, 2-propanol, NaOH) and sampling conditions (cold sampling, desiccation, heat drying) were induced to explore the effects on Raman spectra in order to improve the chemometric models. As a result, in this study nine food-relevant bacteria were exposed to seven stress conditions in addition to routine cultivation as a control. Spectral alterations in lipids, polysaccharides, nucleic acids, and proteins were observed when compared to normal growth circumstances without stresses. Regardless of the involvement of several stress factors and storage times, a model for differentiating the analyzed microorganisms from genus down to strain level was developed. Classification of the independent training dataset at genus and species level for Escherichia coli and at strain level for the other food relevant microorganisms showed a classification rate of 97.6%.

Tween 80™-induced changes in fatty acid profile of selected mesophilic lactobacilli

“…While dihydrosterculic acid ( cyc C19:0, cis -9,10) could potentially be used to differentiate between L. casei and L. paracasei subsp. paracasei MB, the high proportion observed in this study might be due to stress experienced by the bacteria during growth ( Rouch et al, 2002 ; Wu et al, 2020 ; Klein et al, 2022 ). Cyclic fatty acids, including dihydrosterculic acid ( cyc C19:0, cis -9,10), are known markers of stress in LAB.…”

Deuterium isotope probing (DIP) on Listeria innocua: Optimisation of labelling and impact on viability state

“…Raman-DIP can be developed as a tool for the detection of metabolically activity of L. innocua cells in different viability state (VC, VBNC or dead). Raman spectroscopy is already use as an identification tool of stressed and non-stressed foodrelated bacteria [24]. DIP-Raman spectroscopy could have a very useful application in food processing plants to characterize metabolic activity of bacteria from sampling on food matrix or surfaces.…”

Recent advances of Raman spectroscopy for the analysis of bacteria

“…Similar studies were conducted for blood cultures 94 and clinical strains. 95,96 Similar to antibiotics, there are studies that investigated bacterial responses to environmental stressors, 97,98 heavy metals, and herbicides. 99 These studies are also helpful for the understanding of…”

“…Similar to antibiotics, there are studies that investigated bacterial responses to environmental stressors, 97 , 98 heavy metals, and herbicides. 99 These studies are also helpful for the understanding of bacterial inactivation mechanisms and the effect of different stressors or chemicals on bacterial cells.…”