Theses and Dissertations
Date of Award
8-1-2026
Document Type
Thesis
Degree Name
Master of Science (MS)
Department
Chemistry
First Advisor
Veerachandra K. Yemmireddy
Second Advisor
Ahmed Touhami
Third Advisor
Jason Parsons
Abstract
Foodborne pathogens frequently encounter sublethal environmental stresses during food production, processing, and storage, resulting in physiological adaptations that enhance survival and antimicrobial tolerance. Natural antimicrobial compounds have shown considerable potential for controlling foodborne pathogens; however, limited information is available on how these adaptive responses influence bacterial growth dynamics and antimicrobial susceptibility. This thesis investigated the effects of acid (pH 5.5), osmotic (2.5% NaCl), and low-temperature (4 °C) adaptation on the growth dynamics and antimicrobial susceptibility of Salmonella enterica serovar Typhimurium (ATCC 14028) and Listeria innocua (ATCC 15742) after exposure to carvacrol and thymol.
Chapters I and II provide a comprehensive review of foodborne pathogens, bacterial stress adaptation, natural antimicrobial compounds, mechanisms of antimicrobial action, and predictive microbiology approaches for characterizing bacterial growth. In Chapter III, the study evaluated the antimicrobial susceptibility and growth characteristics of stress-adapted and unstressed cells using minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), growth kinetics, and time-kill assays. Results showed that osmotic (2.5% NaCl) and low-temperature (4 °C) adaptation increased bacterial tolerance to carvacrol and thymol, whereas acid adaptation (pH 5.5) had minimal effect on antimicrobial activity. In S. enterica, osmotic and low-temperature adaptation increased the MIC of thymol from 2.50 to 5.00 mM. In L. innocua, osmotic adaptation increased the MIC of carvacrol from 2.50 to 5.00 mM, while low-temperature adaptation increased the MICs of both carvacrol and thymol from 2.50 to 5.00 mM. Growth kinetic analysis demonstrated that physiological stress adaptation altered lag phase duration and maximum specific growth rate, whereas time-kill assays revealed differences in the inactivation kinetics of stress-adapted and unstressed cells during antimicrobial treatment.
Carvacrol and thymol exhibited strong antibacterial activity against both pathogens and predominantly exerted bactericidal effects. Finally, Chapter IV summarizes the major findings, limitations, and future research directions.
Recommended Citation
Puorizaa, T. (2026). Stress Conditioning and Susceptability to Phenolic Antimicrobials in Salmonella Typhimurium and Listeria innocua [Master's thesis, The University of Texas Rio Grande Valley]. ScholarWorks @ UTRGV. https://scholarworks.utrgv.edu/etd/2069
Comments
Copyright 2026 Titus Puorizaa. All Rights Reserved. https://proquest.com/docview/3408996753