Antibiofilm effect of Zanthoxylum armatum DC. essential oil against spoilage Bacillus amyloliquefaciens DY1a

Abstract:

[Background] Bacillus spp. are major aerobic bacteria associated with the spoilage of soy products. They form biofilms at the air-liquid interface to bring about constant microbial contamination to soy food processing line. [Objective] To examine the activity of Zanthoxylum armatum DC. essential oil (ZA-EO) against the growth and biofilm formation of a spoilage bacterium Bacillus amyloliquefaciens DY1a isolated from soy products. [Methods] Gas chromatography-mass spectrometry (GC-MS) was used for the chemical characterization of ZA-EO. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of ZA-EO against DY1a were determined by the microdilution method. The inhibitory effect on extracellular protease activity and biofilm formation and the eradication of preformed biofilm by ZA-EO were evaluated. Scanning electron microscope coupled with 3D optical microscope was used to observe the surface topography and structure changes of the biofilm treated with ZA-EO. Besides, the content of exopolysaccharide and protein in the extracellular polymeric substance (EPS) were measured. The anti-biofilm mechanism of ZA-EO was explored from swimming and swarming motility, cell adhesion and auto-aggregation, cell surface hydrophobicity, and Zeta potential. [Results] ZA-EO mainly contained linalool (52.37%), D-limonene (21.81%), and sabinene (10.94%). The MIC and MBC of ZA-EO against spoilage B.amyloliquefaciens DY1a were 3.2 µL/mL and 12.8 µL/mL, respectively. Additionally, 3.2 µL/mL ZA-EO inhibited the secretion of extracellular protease and the biofilm formation, and showed the eradication efficiency of 25.79% for the preformed biofilm. Moreover, ZA-EO decreased the thickness and surface roughness of the biofilm as well as the content of exopolysaccharide and protein in EPS. Furthermore, ZA-EO treatment significantly weakened the swimming and swarming motility, inhibited cell adhension and auto-aggregation, enhanced the cell surface hydrophobicity, and reduced the surface charge of DY1a. [Conclusion] ZA-EO had activity against the growth and biofilm formation of B.amyloliquefaciens DY1a and exhibited promising eradication of preformed biofilm. The activity ofZA-EO against the biofilm formation of B.amyloliquefaciens can be attributed to the interruption against cell motility, changing of cell surface characteristics, and inhibition on cell adhension and auto-aggregation during the early stage, as well as the reduction of exopolysaccharide and protein content in EPS.