Assessment of antimicrobial activity of Nα-lauroyl arginate ethylester (LAE®) against Yersinia enterocolitica and Lactobacillus plantarum by flow cytometry and transmission electron microscopy

N-alpha-lauroyl arginate ethylester, LAE (R), which was approved as GRAS by the US Food and Drug Administration (FDA) and by the European Food Safety Authority (EFSA) in 2007, is a surfactant that exhibits antimicrobial activity. To assess its antimicrobial effect, treated cell suspensions of Yersinia enterocolitica and Lactobacillus plantarum were analysed for reduction of cell viability. Membrane dysfunction was determined by staining with bis-oxonol to detect the loss of membrane potential, and with propidium iodide to detect permeabilized membranes by flow cytometry. LAE (R) treatment for 30 min induced a 4 log(10) reduction in cell viability in both bacteria; different subpopulations with variable degrees of cellular damage were observed by flow cytometry. Permeabilized membranes suggested the leakage of cellular material; this was also indicated by the loss of potassium ion(s), which was higher in L. plantarum than in Y. enterocolitica. Structural changes involving collapse of the cytosol and alterations of the cellular envelopes, mainly in Y enterocolitica, and the formation of mesosomes in L. plantarum were observed by transmission electron microscopy. (C) 2015 Elsevier Ltd. All rights reserved.