Comparative analysis of Listeria monocytogenes biofilm formation and characterization of cell viability and biofilm structure.

摘要

This thesis investigated biofilm formation by five strains of Listeria monocytogenes. Biofilms were grown in static conditions at 37°C for up to 10 days. The cell counts increased for the first two days with all strains, but after 2 days the counts decreased for all strains except for one. Biofilm cells of one strain continued to increase for 4 days. Results from direct viable count were consistently 0.5 log10 higher than those obtained with plate count, indicating that some L. monocytogenes in these biofilms were viable but non-culturable cells. Confocal scanning laser microscopy (CSLM) revealed that the static biofilms consisted of two distinct layers with 0.5 log10 higher cell numbers in the bottom layer compared to the upper layer. L. monocytogenes biofilms grown in a continuous flow system formed a classical mushroom like structure similar to that observed with Pseudomonas spp. in flowing water systems. CSLM demonstrated that the extracellular polymeric substances of a 10-day L. monocytogenes biofilm consisted of galactose, mannose and glucose.