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Thesis
Investigating stringent response-mediated tolerance to non-thermal plasma in Escherichia coli
Master of Science (M.S.), Drexel University
Jul 2025
DOI:
https://doi.org/10.17918/00011122
Abstract
The alarming rise in bacterial resilience to antibiotics stems from overuse and misuse. One survival strategy bacteria employ is dormancy, a metabolically quiescent state triggered by the stringent response (SR). The SR is a highly conserved stress signaling pathway used to mitigate the effect of external stressors by shifting gene regulation from active division to dormancy and stress responses within the RpoS regulon. Recently, non-thermal plasma (NTP), partly ionized gas containing ultraviolet (UV) rays, ozone, and charged reactive species, has emerged as a promising alternative to antibiotics. NTP and its multiple effectors have shown to be effective against biofilms -- a major source of these dormant populations -- but the impact of the SR on NTP efficacy is unclear. This study investigates the SR and the RpoS regulon using single-gene knockouts from the Escherichia coli K12 Keio collection. To quantify viable cell populations, we pretreated various E. coli strains with serine hydroxamate (SHX), a known SR inducer, or water, followed by NTP exposure. Colony counts revealed that deleting rpoS and its regulated oxidative stress response gene xthA significantly reduced viable cell counts. Surprisingly, deleting the primary SR gene, relA, increased colony-forming units (CFU) yields in SHX-treated cells exposed to NTP. These findings highlight the critical role of the RpoS regulon and suggest that RelA-independent pathways significantly contribute to reduced NTP susceptibility. This work lays the framework for identifying bacterial responses that may influence the long-term efficacy of NTP.
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Details
- Title
- Investigating stringent response-mediated tolerance to non-thermal plasma in Escherichia coli
- Creators
- Lauren Elizabeth Walsh
- Contributors
- Donald C. Hall Jr. (Advisor) - Drexel University, Microbiology and ImmunologyVandana Miller (Advisor)
- Awarding Institution
- Drexel University
- Degree Awarded
- Master of Science (M.S.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- vii, 42 pages
- Resource Type
- Thesis
- Language
- English
- Academic Unit
- Microbiology and Immunology; College of Medicine; Drexel University
- Other Identifier
- 991022072695204721