Exploring the phenomenon of filamentation in Listeria monocytogenes
LE3 .A278 2020
Bachelor of Science
Listeria monocytogenes is an opportunistic food-borne pathogen which displays tolerances to a plethora of stress factors, that allows it to persist in harsh environments. Listeria monocytogenes strain Lm568, originally isolated from a food processing environment, was exposed to cold and acid stress and subsequently developed colonies with atypical morphology relative to its wild type. Further examination of the cells from these colonies under the microscope revealed an elongated phenotype. Filamentation is a stress response that has been documented in a variety of bacteria, including L. monocytogenes when subjected to difficult conditions. However, little is known about the relevance of this state in the context of food safety. For example, do these filamented cells form septa and revert to normal cells, thereby increasing the infected dose if ingested. If not, what is the virulence capacity of the cells in the elongated state. In this study experiments were performed to shed light on these questions. A virulence assay, microscopy, growth kinetic assays, and other characterization tests were applied to wild type strain Lm568 (Lm568WT) and its filamemented phenotype (Lm568F) with the aim of assessing the risk Lm568F could pose as a food pathogen compared to its wild type counterpart. Filamentation in this strain of L.monocytogenes appears to result in less virulence, despite the mutant being just as metabolically active as the original Lm568WT strain. During this study, a morphological variant, distinguishable by its short-curved rod morphology,was found to have derived from samples of Lm568F, suggesting this strain is able to revert from the filamented state under certain stress conditions. Overall, this variant named Lm568D, also appears to be less virulent than Lm568WT and may pose less of a risk to food safety than Lm568WT.
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