Date of Award

Spring 5-8-2023

Document Type


Degree Name

Bachelor of Arts



First Advisor

Joan L. Slonczewski


Multidrug efflux pumps like AcrAB-TolC, MdtEF-TolC, and EmrAB-TolC protect Escherichia coli and other Gram-negative bacteria when they are first exposed to antibiotics in the human gut. Natural membrane-permeant antimicrobials like methyl salicylate, bile acids, sorbate, benzoate, and salicylate are commonly found in the human gut and can eliminate or promote the prevalence of these drug pumps via their selective effects. The selective effects of these membrane-permeant compounds on are affected by many factors, one of which is their effects on the expression of the drug pumps. To understand the effects of membrane-permeant compounds, environmental pH, growth phases, and their interactions on the expression of acrA, mdtE, and emrA, we developed a multiplex plate-based digital PCR assay and discovered an alternate expression pattern among the drug pump genes. Across moderately acidic to basic pH (5.5 – 8.0), mdtE mRNA expression was elevated in early stationary phase, while acrA and emrA mRNA expression was elevated in log growth phase. Moderate acid (pH 5.5) also log-phase mdtE mRNA expression. These expression patterns of the drug pump genes may correlate with the drug pumps’ contribution to E. coli MDR. At neutral pH, bile acids, the common substrates of all three drug pumps upregulated mdtE expression in early stationary phase and acrA and emrA expression in log growth phase. Further experiments with phytochemicals suggested that the effects of membrane-permeant organic acids like sorbate, benzoate, and salicylate on drug pump expression were dependent upon environmental pH levels.

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Available for download on Tuesday, June 04, 2024