Mississippi State University
Shekhar Sharma, Chander
Date of Degree
Original embargo terms
Visible to MSU only for 2 years
Dissertation - Campus Access Only
Food Science and Technology
Doctor of Philosophy
College of Agriculture and Life Sciences
Department of Food Science, Nutrition and Health Promotion
Listeria monocytogenes is an important foodborne pathogen that can adapt to stress conditions to persist in food processing environments. Our findings show that there was a development of low-level tolerance to quaternary ammonium compound (QAC) and antibiotics ciprofloxacin and trimethoprim in L. monocytogenes after sublethal adaptation to QAC. Using eight L. monocytogenes strains, we determined the changes in MIC, growth rate, and surviving CFU for homologous and heterologous stress-response after sublethal exposure to daily cycles of fixed or gradually increasing concentration of QAC. Three main findings were observed: (1) Short-range MIC of QAC, ciprofloxacin, and trimethoprim increased by 1.6 to 2.3, 1.5 to 2.9, and 1.7 to 2.5 fold against QAC-adapted phenotypes of L. monocytogenes as compared to the non-adapted cells; (2) QAC-adapted phenotypes of L. monocytogenes exhibited a significant increase in growth rate by 2.5 to 7.1, 2.1 to 6.8, or 1.4 to 4.8 fold in the broth model containing QAC, ciprofloxacin, or trimethoprim respectively, as compared to non-adapted cells; and (3) QAC-adapted phenotypes of L. monocytogenes exhibited a significant increase in survival by 1.5 to 4, 2.2 to 4.3, or 1.3 to 3.2 log CFU/ml in the agar model containing QAC, ciprofloxacin, or trimethoprim respectively, as compared to non-adapted cells (P < 0.05). There were strain differences in QAC-adapted phenotypes of L. monocytogenes for both homologous and heterologous stress-response with some strains exhibiting a significant increase in short-range MIC, growth rate, and survival while others exhibiting no changes as compared to non-adapted cells. These findings suggest the potential formation of low-level QAC-tolerant and antibiotic-tolerant phenotypes in some L. monocytogenes strains under residual QAC concentrations (where QAC may be used widely) and such cells if not inactivated may survive longer to increase food safety risk.
This research was supported in part by NIFA-USDA grant (under the award number 2016-69003-24600) and Food Safety Initiative Award (under grant number USDA-ARS SCA No. 58-6402-2729) to Mississippi Agricultural and Forestry Experiment Station (MAFES) under projects MIS-401180 and MIS-401210
Kode, Divya Satish, "Homologous and heterologous stress adaptation in Listeria monocytogenes after sublethal exposure to quaternary ammonium compound" (2021). Theses and Dissertations. 5117.