Listeria monocytogenes exposed to antimicrobial peptides displays differential regulation of lipids and proteins associated to stress response.

With the onset of Listeria monocytogenes resistance to the bacteriocin nisin, the search for alternative antimicrobial treatments is of fundamental importance. In this work, we set out to investigate proteins and lipids involved in the resistance mechanisms of L. monocytogenes against the antimicrobial peptides (AMPs) nisin and fengycin. The effect of sub-lethal concentrations of nisin and lipopeptide fengycin secreted by Bacillus velezensis P34 on L. monocytogenes was investigated by mass spectrometry-based lipidomics and proteomics. Both AMPs caused a differential regulation of biofilm formation, confirming the promotion of cell attachment and biofilm assembling after treatment with nisin, whereas growth inhibition was observed after fengycin treatment. Anteiso branched-chain fatty acids were detected in higher amounts in fengycin-treated samples (46.6%) as compared to nisin-treated and control samples (39.4% and 43.4%, respectively). In addition, a higher relative abundance of 30:0, 31:0 and 32:0 phosphatidylglycerol species was detected in fengycin-treated samples. The lipidomics data suggest the inhibition of biofilm formation by the fengycin treatment, while the proteomics data revealed downregulation of important cell wall proteins involved in the building of biofilms, such as the lipoteichoic acid backbone synthesis (Lmo0927) and the flagella-related (Lmo0718) proteins among others. Together, these results provide new insights into the modification of lipid and protein profiles and biofilm formation in L. monocytogenes upon exposure to antimicrobial peptides.

Fate of enniatins in the Ale beer production stages analyzed by a validated method based on matrix-matched calibration and LC-QToF-MS.

Enniatins (ENA, ENA1, ENB and ENB1) are emerging mycotoxins reported in malt used for brewing. This study aimed to assess the fate of ENA, ENA1, ENB and ENB1 throughout Ale beer brewing using a validated method based on matrix-matched calibration (MMC) and liquid chromatography with quadrupole time-of-flight mass spectrometry detection. MMC avoided the inaccurate quantification of all enniatins, since the matrix effects that cause signal suppression have been overcome. The validated method displayed linearity (R2 > 0.99), recovery (>88%), repeatability and intermediate precision (RSD < 9.0%) in accordance with the different guidelines of method validation. The values of LOD (<0.1 µg kg-1) and LOQ (<0.5 µg kg-1) were sensitive enough to detect enniatins throughout brewing. In the Ale beer production stages, enniatins levels were significantly reduced, ensuring that beers were free of these mycotoxins. In contrast, enniatins were found in all by-products of beer production due to their low water solubility.