Jack Clifford Weis



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Propionate is a common food preservative and one of the major short chain fatty acids in the human intestines. Therefore, exposure to propionate is a frequent event for foodborne pathogens and likely takes place under suboxic conditions. However, it is not clear whether the absence of oxygen affects how pathogens respond to propionate. In this study, we investigated how propionate exposure affects Listeria monocytogenes growth and virulence factor production under aerobic or anaerobic conditions. Under anaerobic conditions, propionate supplementations had no effect on planktonic growth but resulted in decreased adherent growth. In contrast, under aerobic conditions, propionate supplementations resulted in a pH-dependent inhibition of planktonic growth and increased adherent growth. The effects of propionate on planktonic growth are also temperature-sensitive. At room temperature, propionate supplementation resulted in decreased doubling times under aerobic but not anaerobic conditions. To begin to investigate the effects of oxygen on L. monocytogenes response to propionate, we further noted that supernatant from cultures grown with propionate contained an increased amount of acetoin under aerobic conditions and a decreased amount of ethanol under both aerobic and anaerobic conditions. Moreover, L. monocytogenes grown with propionate exhibited an increased proportion of odd number straight chain fatty acids in a manner that was more pronounced under anaerobic conditions. Finally, aerobic suppression of listeriolysin O (LLO) production and anaerobic induction of LLO production were observed in L. monocytogenes grown with propionate. These results clearly demonstrate for the first time that L. monocytogenes exposure to propionate resulted a variety of physiological and pathogenic responses. Moreover, the presence or absence of oxygen plays a critical role in shaping L. monocytogenes responses to propionate that can potentially impact bacterial survival in the environment and subsequent interactions within host cells.

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Project Designation

Honors Thesis

Primary Advisor

Erica Marie Rinehart, Yvonne Y. Sun

Primary Advisor's Department



Stander Symposium project

Propionate Perturbation of Listeria monocytogenes Growth and Listeriolysin O Production is Modulated by Anaerobicity