| L. monocytogenes is a Gram-positive bacterium, ubiquitously distributed in the environment. It is the etiologic agent of listeriosis, a food-borne disease affecting humans and a variety of vertebrates. L. monocytogenes can form biofilm which is a multi-cellular layer of adherent bacteria surrounded by an extracellular polysaccharide matrix. Biofilm bacteria are extremely resistant to sanitizers and are difficult to be eradicated, therefore posing a big challenge to food processing industry and food service department.;In this work, we tested the biofilm formation in a number of L. monocytogenes serotypes under different environmental conditions, such as temperatures, pH and media (BHI, LB, HTM, 1:10 dilution of BHI). We found different serotypes or strains require different conditions to form more biofilm, although most of the strains prefer forming more biofilm under 37°C in HTM medium. We also demonstrated under pH=9 or pH=7.4, all strains (10403S, ΔflaA, MAC, LO28, ATCC19115, ScottA) formed more biofilm compared to pH=3 or pH=5.;We also studied the relation between stress responses and biofilm formation by testing several mutants (Δlmo0423, ΔhtrA , ΔprfA, ΔcodY) relative to stress responses but found the biofilm formation of these mutants were at the same level as the L. monocytogenes wild type strain 10403S.;We also investigated the relation between the PrfA regulator and biofilm formation by testing biofilm formation of different prfA mutants: ΔprfA, the in-frame deletion strain; NF-L924 and NF-L943, the hyper-PrfA activate strains.;Our study gave us a better understanding of how environmental factors affect the L. monocytogenes biofilm formation, providing the basis of food contamination control in food industries. |
