Morphological transitions of Bacillus subtilis in the presence of food‐grade lipidic nanoemulsions

Abstract

The present study aims to study the antibacterial activity of food-grade lipidic nanoemulsion (noncationized/cationized) against Bacillus subtilis (BS). Bactericidal activity was ascertained by studying the morphological transitions on BS using transmission electron microscopy (TEM), atomic force microscopy (AFM), and scanning electron microscopy (SEM). Morphological changes were witnessed by cell wall breakage, oozing out of cellular contents, loss of cell turgidity and contour. Furthermore, aggregation of cationic nanoemulsion (CaNM) was preferentially observed at apical side of BS construing comparatively more electrostatic attraction between electronegative apical side and CaNM. Resistance response of BS exhibited by apical cell-wall thickening was not able to protect the bacteria due to leakage of cellular content. AFM corroborated its importance in bacteriology, wherein the fragmented cell wall can be "piece-by-piece" identified and sutured back to its appropriate vacant places, thereby, completing the cell wall contour of the ghost cell. Such postmortem analysis of bacterial cell using AFM studies can throw light toward mechanism of cell fragmentation of bacterial cells. SEM study also demonstrated the deformed, fragmented, and amorphous nature of BS construing the bactericidal effect of prepared nanoemulsion.

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“…Finally, in one of the newer studies, it was demonstrated that AFM application in microbiological research should also include postmortem analysis of antibiotic-treated bacteria. Such an approach was engaged by Singh et al In their paper, the authors aimed to examine the bactericidal effect of food-grade lipidic nanoemulsion (noncationized/cationized) using B. subtilis as a model bacterium [73]. As expected, TEM, SEM, and AFM analysis revealed nanoemulsion-induced morphological transitions in the treated bacteria, including cell wall destruction and leakage of intracellular content.…”

“…Nevertheless, only by using AFM was it possible to identify piece-by-piece the fragmented cell wall and to locate it in its appropriate vacant places, thus completing the cell wall contour of the ghost cell. Therefore, AFM studies are particularly important in the context of investigation of the bacterial cell fragmentation mechanisms [73]. Finally, in one of the newer studies, it was demonstrated that AFM application in microbiological research should also include postmortem analysis of antibiotic-treated bacteria.…”

“…Nevertheless, only by using AFM was it possible to identify piece-by-piece the fragmented cell wall and to locate it in its appropriate vacant places, thus completing the cell wall contour of the ghost cell. Therefore, AFM studies are particularly important in the context of investigation of the bacterial cell fragmentation mechanisms [73].…”

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“…Several case studies have confirmed severe health impacts associated with the consumption of Bacillus spp. contaminated food ( Singh N. et al, 2020 ). There are many reports related with the in vitro studies of EO nanoemulsions against different Bacillus spp.…”