Purpose: This study investigates the effect of 3 polysaccharides at different concentrations and their hydrolyzing enzymes on the formation of biofilms by selected strains of L. monocytogenes over a period of 120h.
Methods: Biofilms were developed in polystyrene tissue culture plates by 4 food isolates and 4 disease outbreak isolates of L. monocytogenes strains in tryptose soy broth (TSB) with 3 different concentrations (0, 0.02 and 0.04%) of pectin, cellulose or starch and with or without the addition of pectinase, cellulose or amylase at 37°C during a period of 24 to 120h. The biofilms formed were quantified using the Crystal Violet Binding Assay. The influence of polysaccharides, their hydrolyzing enzymes and incubation time on biofilm formation was analyzed at a confidence level of 95% using a multifactorial design of the Statistical Analysis Software.
Results: Presence of external polysaccharides negatively affected biofilm formation. Increase in polysaccharide concentration did not have a significant influence on biofilm formation by the Listeria strains. Addition of pectin, cellulose and starch hydrolyzing enzymes led to a significant increase in biofilm mass. Generally, the foodborne isolates (0.171-0.284) formed more biofilms than did the diseases outbreak isolates (0.086-0.100) used in the study. Biofilm formed by the L. monocytogenes strains in TSB with or without polysaccharide-hydrolyzing enzymes increased significantly with incubation time starting from the 72h sampling point and forwards.
Significance: The research provides knowledge on how Listeria biofilm formation is regulated by external polysaccharides and their hydrolyzing enzymes.