Life Sciences Commons^™

Influence Of External Ph And Organic Acids On Internal Ph And Acid Anion Accumulation In Listeria Monocytogenes And Escherichia Coli, Savannah R. Branson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Listeria monocytogenes and Escherichia coli are both among the most common microbial pathogens that cause foodborne illnesses and death. They both are capable of growing over a wide range of conditions. Organic acids are widely employed in the food industry to control growth of these pathogens to help prevent foodborne illnesses. There is substantial evidence that intracellular accumulation of organic acid anions is a major inhibitor to cell growth, and that many bacteria may combat anion accumulation by lowering their intracellular pH (pH_i). In this study, we followed the accumulation of acid anion into the cell pellet and …

Phosphodiesterase D Is Involved In Bile Resistance In Listeria Monocytogenes, Sophia A. Ali

Honors Theses

Listeria monocytogenes is a deadly foodborne bacterium that is responsible for almost 20% of food-related deaths in the United States. Listeria monocytogenes contaminates ready-to-eat products such as cheese, deli meat, and ice cream. Once ingested, it invades the intestinal lining and can enter the bloodstream, causing listeriosis. There is a gap in the knowledge of the pathogenesis of L. monocytogenes in how it is able to survive in the gastrointestinal tract in the presence of bile, which has bactericidal properties. Previous studies have suggested that the second messenger cyclic-dimeric-GMP may be involved in the regulation of virulence factors of Listeria. …

The Impact Of Oxygen Availability And Oxidative Stress On Regulation Of Cyclic-Dimeric-Gmp In Listeria Monocytogenes Strain F2365, Anna G. Welch

Honors Theses

Listeria monocytogenes is a gram-positive foodborne pathogen that results in the infectious disease listeriosis. The second messenger molecule cyclic-dimeric-GMP has been found to be responsible for the regulation of expression of many of its virulence factors with diguanylate cyclases and phosphodiesterases regulating the intracellular concentration of cyclic-di-GMP through synthesis and degradation, respectively. This study investigated the possibility that the availability of oxygen is the environmental signal crucial to the regulation of these enzymes. Prior research in our laboratory has demonstrated that the intracellular concentration of cyclic-di-GMP is elevated when exposed to anaerobic conditions. Due to this, it was hypothesized that …

Effect Of Contact Time And Attachment Level Of Bacterial Pathogens On Efficacy Of Chlorine Treatment In Fresh Produce, Jyoti Aryal

LSU Master's Theses

Bacterial attachment or biofilm formation on produce surfaces may result in limited penetration ability of sanitizers. This study examined the wet and dry contact time (WCT or DCT) of produce during washing with sanitizer and evaluated the effect of attachment level of Listeria monocytogenes during storage on the efficacy of chlorine treatment. Spinach and bell peppers were inoculated with Listeria monocytogenes and Salmonella enterica. The produce was then washed by dipping into a 100 ppm of chlorine solution for 1 min and an additional 1, 3, or 5 minutes (WCT) or removed from the chlorine solution and held for 1, …

Predicting, Monitoring And Controlling The Growth Of Listeria In Complex Food Matrices, Laura Mary Nyhan

Theses

Listeria monocytogenes is a foodborne pathogen which is a significant challenge in food production, particularly for ready-to-eat (RTE) products. Incidence of Listeria in RTE foods can be reduced by the application of intelligent combinations of preservative factors or hurdles, while data quantifying the efficacy of hurdle combinations can be exploited and used in the area of predictive microbiology. Traditional culture-based techniques, such as viable plate counts, are commonly used to monitor the growth/survival of microorganisms in foods, however these methods are tedious, time-consuming and due to their destructive nature, are associated with low reproducibility and high variability. Therefore, rapid, non-invasive …

Biofilm Sanitizer Tolerance Of Vermont Dairy Listeria Monocytogenes, Emily C. Forauer

Graduate College Dissertations and Theses

Listeria monocytogenes is a foodborne pathogen found in biofilms on surfaces and equipment in the food processing environment. Sodium hypochlorite (SH) and quaternary ammonium compounds (QAC) are readily available and commonly used sanitizers. However, due to the structure and additional organic material produced in a biofilm, killing bacteria within the biofilm may be a challenge for one or both of these sanitizers.

The objective of this work was to determine if immature and mature biofilms from L. monocytogenes isolated from Vermont artisan dairy environments were more tolerant to QAC and SH compared to planktonic cultures’ tolerance. To determine sanitizer minimum …