Characterization and application of antimicrobials produced by Enterococcus faecium S6 isolated from raw camel milk

The emergence of antimicrobial resistance in the food chain and the consumer's demand for safe food without chemical preservatives have generated much interest in natural antimicrobials. Thus, our main goal was to study the mode of action of the crude extract, the enterocins, and the organic acid produced by a bacteriocinogenic Enterococcus faecium strain S6 previously isolated from raw camel milk. Then, we aimed to evaluate their potential application in a food system. These antimicrobials exhibited antimicrobial activity against Listeria monocytogenes, Salmonella enterica, and Escherichia coli. The enterocins were synthesized as primary metabolites beginning at the lag phase, with optimal production at the exponential and stationary phases. The antimicrobials had a direct effect in extending the lag phase of L. monocytogenes, along with a significant inhibitory activity. The organic acid, in particular, inhibited both L. monocytogenes and S. enterica by inducing a total lysis and damage of the cell wall. The enterocins acted on disrupting the cell wall with pore formation, leading to cell death. Moreover, the crude extract revealed a combined inhibitory activity between enterocins and organic acid. Furthermore, the antimicrobials showed promising results through inhibiting L. monocytogenes cells in milk samples up to 1 wk at 4°C.