Extracellular crude polysaccharide of Limosilactobacillus fermentum CSC-19 inhibits the biofilm formation of Listeria monocytogenes

Abstract:

[Objective] To screen out the lactic acid bacteria that can inhibit the biofilm formation of Listeria monocytogenes (LM), identify the active component of the bacteria, and analyze the function of the active component. [Methods] We employed crystal violet staining to screen out the lactic acid bacteria of which the extract could inhibit the biofilm formation of L. monocytogenes. We analyzed the potential active component that inhibited biofilm formation by acid neutralization, protease treatment, and heat treatment and hypothesized that the main active component was extracellular crude polysaccharide (ECP). We then employed ethanol precipitation to extract the ECP from the lactic acid bacteria and analyzed the inhibitory activity of ECP on the biofilm formation and growth of L. monocytogenes. The morphology and structure of the biofilm treated with ECP were characterized by laser confocal scanning microscopy and scanning electron microscopy. [Results] The inhibition rate of Limosilactobacillus fermentum CSC-19 fermentation supernatant on the biofilm formation of L. monocytogenes 1516-2LM was 81.7%. After heat treatment and protease treatment, the activity of the fermentation supernatant did not significantly change (P>0.05), which indicated that the active component in the fermentation supernatant may be ECP. ECP inhibited the biofilm formation of L. monocytogenes in a concentration-dependent manner, while it did not inhibit the growth of L. monocytogenes. The results of confocal laser scanning microscopy and scanning electron microscopy showed that ECP destroyed the three-dimensional and honeycomb-structured biofilm and left only a few scattered adherent cells on the surface of the glass slide. [Conclusion] The ECP of L. fermentum CSC-19 inhibits the biofilm formation of L. monocytogenes, which is expected to be applied to the prevention and control of food contamination.