Antibiotics Susceptibility Phenotyping and Extracellular Polymeric Substances Production of Listeria monocytogenes Biofilm and Planktonic Cells

The present research aimed to compare the susceptibility of L. monocytogenes planktonic cells and three different ages (10, 40 and 90 days-old) of biofilm to antibiotics. A second objective was to determine the relationship between the amount of produced EPS by L. monocytogenes biofilm and antibiotic susceptibility of L. monocytogenes biofilm. The extraction of EPS was carried out by using a cation exchange resin method and exopolysaccharides content in crude EPS was determined using phenol-sulfuric acid method. Antibiotic susceptibility of L. monocytogenes biofilm and planktonic cells were performed by the standard disk diffusion method. The maximum amount of exopolysaccharides was determined (411.5 mu g/cm(2)) in 90 days-old L. monocytogenes biofilm collected from iron pipe. While, the minimum amount (203.4 mu g/cm(2)) was in Cu pipe. Regarding to the antibiotic susceptibility results, it was found that, L. monocytogenes plankton cells were more sensitive to the tested antibiotic than L. monocytogenes biofilm. Also, it was found that, 90 days-old L. monocytogenes biofilm collected from iron pipe was more resistant to all tested antibiotics than which collected from Cu pipe. The findings in this research provide useful information and background data on the role of EPS in antibiotic resistance of L. monocytogenes biofilm.