Cyclic dipeptide cyclo(L-leucyl-L-prolyl) from marine Bacillus amyloliquefaciens mitigates biofilm formation and virulence in Listeria monocytogenes

This study was intentionally focused on cyclo(L-leucyl-L-prolyl) (CLP), a cyclic dipeptide with myriad pharmaceutical significance, to explore its antivirulence efficacy against the predominant foodborne pathogen, Listeria monocytogenes (LM). Minimum inhibitory concentration (MIC) of CLP against LM ATCC 19111 was found to be 512 mu g mL(-1). CLP at sub-MICs (64 128, 256 mu g mL(-1)) demonstrated a profound non-bactericidal dose-dependent antibiofilm efficacy (on polystyrene and glass) against LM, which was further confirmed through confocal and scanning electron microscopic analysis (on stainless steel surface). In vitro bioassays divulged the phenomenal inhibitory efficacy of CLP towards various virulence traits of LM, specifically its overwhelming suppression of swimming and swarming motility. Data of in vivo assay using Caenorhabditis elegans signified that the plausible mechanism of CLP could be by impeding the pathogen's initial adhesion and thereby attenuating the biofilm assemblage and its associated virulence. This was further confirmed by significant decrease in extracellular polymeric substance, autoaggregation, hydrophobicity index and extracellular DNA of the CLP-treated LM cells. Collectively, this study unveils the antivirulence efficacy of CLP against the Gram-positive foodborne pathogen and the strain Bacillus amyloliquefaciens augurs well to be a promising probiotic in controlling infections associated with LM.