Morphological change and decreasing transfer rate of biofilm-featured Listeria monocytogenes EGDe

Authors: LEE, YUEJIA - Mississippi State University; WANG, CHINLING - Mississippi State University

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2016
Publication Date: 2/15/2017
Citation: Lee, Y., Wang, C. 2017. Morphological change and decreasing transfer rate of biofilm-featured Listeria monocytogenes EGDe. Journal of Food Protection. 80:368-375.

Interpretive Summary: Listeria monocytogenes cause food-borne illness and the bacterium has the ability to resist the hostile food-processing environment and, thus, frequently contaminates ready-to-eat foods. It is commonly accepted that L. monocytogenes’ tendency to generate biofilms on various surfaces enhances its resistance to the harshness of the food-processing environment and survive and further contaminate food during processing. In this study, we examined the growth of Listeria biofilms on stainless-steel surfaces and its effect on L. monocytogenes EGDe’s transferability. We found a distinct change of morphology of L. monocytogenes EGDe at the late stage of biofilm formation. More importantly, once food is contaminated by L. monocytogenes EGDe, the bacterium can continue to grow at at 4°C regardless the initial level of contamination, even if L. monocytogenes EGDe’s contamination was initially very low.

Technical Abstract: Listeria monocytogenes, a lethal foodborne pathogen, has the ability to resist the hostile food-processing environment and, thus, frequently contaminates ready-to-eat foods during processing. It is commonly accepted that L. monocytogenes’ tendency to generate biofilms on various surfaces enhances its resistance to the harshness of the food-processing environment. However, the role of biofilm formation on L. monocytogenes EGDe’s transferability remains controversial. We examined the growth of Listeria biofilms on stainless-steel surfaces and its effect on L. monocytogenes EGDe’s transferability. The experiments were a factorial 2 × 2 design with at least three biological replicates. Through scanning electron microscopy, a mature biofilm with intensive aggregates of cells was observed on the surface of stainless steel after three or five day incubation, depending on the initial level of inoculation. During biofilm development, L. monocytogenes EGDe carried out binary fission vigorously before a mature biofilm was formed and subsequently changed their cellular morphology from rod-shape to sphere-shape. Furthermore, static biofilm, which was formed after a three-day incubation at 25°C, significantly inhibited the transfer rate of L. monocytogenes EGDe from stainless-steel blades to 15 bologna slices. During a seven-day storage at 4°C, however, bacterial growth rate was not significantly impacted by that whether bacteria were transferred from biofilm and the initial concentrations of transferred bacteria on the slice. In conclusion, this study is the first to report a distinct change of morphology of L. monocytogenes EGDe at the late stage of biofilm formation. More importantly, once food is contaminated by L. monocytogenes EGDe, contamination proceeds independently of biofilm development and the initial level of contamination when food is stored at 4°C, even if L. monocytogenes EGDe’s contamination was initially undetectable before storage.