Date of Award


Document Type


Degree Name

Master of Science (MS)

Legacy Department


Committee Chair/Advisor

Cao, Min

Committee Member

Hughes , Thomas

Committee Member

Dong , Yuqing


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.

Included in

Microbiology Commons



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