Date of Completion


Embargo Period



Dr. Mary Anne Amalaradjou, Dr. Dennis D'Amico

Field of Study

Animal Science


Master of Science

Open Access

Open Access


Bacterial pathogens, such as Salmonella and Listeria monocytogenes, can contaminate agricultural soil thereby increasing the risk of produce-associated foodborne outbreaks. In this study three plant-derived antimicrobials (PDAs), carvacrol (CR), thymol (TY), and β-resorcylic acid (BR) were analyzed for their efficacy in reducing Salmonella and L. monocytogenes in agricultural soil. The effect of the PDAs on the soil pH, nutrients, and microbiome was also determined.

Sandy loam soil was inoculated with either Salmonella or L. monocytogenes followed by the addition of 0.25 or 0.5% CR, TY, and BR. The treated samples were analyzed up to 21 days for surviving pathogens. The effect on the soil pH and nutrients of 0.5% CR, TY, and BR was determined also for up to 21 days. The effect of 0.5% CR and TY on the microbiome was analyzed by DNA extraction from soil samples for up to 42 days.

All three compounds were effective in reducing both Salmonella and L. monocytogenes. Both pathogens were reduced to undetectable levels by 0.25 and 0.5% CR and TY by day 1 (P < 0.05). None of the treatments resulted in soil nutrients outside of normal limits although BR did decrease the pH (P < 0.05). The addition of CR and TY had no significant deleterious effects on the soil microbiome and increased the population of some groups of beneficial soil bacteria (P < 0.05).

CR, TY, and BR could potentially be used as soil amendments to reduce Salmonella and L. monocytogenes in agricultural soil. Further studies are necessary to determine the PDAs' environmental fate and effect on plant health.

Major Advisor

Dr. Kumar Venkitanarayanan