Enterococcus mundtii A9-1A with antagonistic effect on Listeria monocytogenes: screening and characterization of antimicrobial activity of its bacteriocin

Abstract:

[Background] Listeria monocytogenes is a major food-borne pathogen, causing the mortality rate of 20%–30% in susceptible populations. [Objective] To screen the lactic acid bacteria with antagonistic effect on L.monocytogenes and explore the physicochemical properties and killing effect of the bacteriocin produced by the isolate on L.monocytogenes. [Methods] The bacteriocin-producing lactic acid bacteria with antagonistic effect on L.monocytogenes were screened by the Oxford cup method. The strain screened out was identified based on morphological characteristics, 16S rRNA gene sequencing, and average nucleotide identity (ANI). The physicochemical properties of the bacteriocin produced by the strain were analyzed and the antagonistic effect of the bacteriocin crude extract on L.monocytogenes was characterized by laser confocal microscopy and scanning electron microscopy. [Results] A strain A9-1A with strong antagonistic effect on L.monocytogenes was obtained, with the inhibition zone diameter of 37.56 mm and antagonistic effects on Listeria and Enterococcus faecalis. It was identified as Enterococcus mundtii. The bacteriocin produced by this strain could tolerate strong acids and alkali (pH 2.0–11.0) and high temperatures (37–121 ℃). It was not sensitive to amylase and lipase but sensitive to proteases. The minimum inhibitory concentration of the bacteriocin crude extract was 16 μg/mL. The results of confocal laser scanning microscopy and scanning electron microscopy showed that the bacteriocin crude extract damaged the cell membrane and led to the formation of holes, causing the leakage of cell contents and thereby killing L.monocytogenes. [Conclusion] A bacteriocin-producing strain E. mundtii A9-1A with strong antagonistic effect on L.monocytogenes was screened out. Its bacteriocin could tolerate strong acids and alkali and high temperatures, demonstrating the application potential in the prevention and control of L.monocytogenes contamination in food production.