The Role of the Rcs Phosphorelay in the Development of Antibiotic Resistance

Open Access
Author:
Gao, Geoffrey Siyuan
Area of Honors:
Biochemistry and Molecular Biology
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Sarah Ellen Ades, Thesis Supervisor
  • Ming Tien, Honors Advisor
  • Scott Brian Selleck, Faculty Reader
Keywords:
  • Rcs phosphorelay
  • Antibiotic Resistance
  • Cell Envelope Stress Response
  • rcsB
  • rcsA
  • Beta-lactam antibiotics
  • Cefsulodin
Abstract:
Antibiotic resistance levels of pathogenic bacteria have increased drastically since antibiotics were first introduced and render many antibiotics completely ineffective. Understanding how bacteria become resistant is crucial for developing new drug therapies or finding new drugs that inactivate these mechanisms. This research focuses on the Rcs phosphorelay, a cell envelope stress response that potentially contributes to antibiotic resistance. Finding how often this pathway is utilized and what proteins are crucial for resistance can help deduce how this pathway increases antibiotic resistance. Initially, E. coli mutants resistant to cefsulodin, a β-lactam antibiotic, were isolated from different concentrations of cefsulodin. All mutants tested were found to be resistant on plates but not in liquid, indicating a resistance mechanism that was activated by surface contact. These mutants were then tested for dependence on the Rcs phosphorelay by deleting rcsB because rcsB is the central mediator of the pathway that helps form the transcriptional factors. Without rcsB, the pathway is inactive. Most of the mutants with high resistance levels had a large reduction in resistance when the Rcs phosphorelay was inactivated, which indicates a strong dependence on the pathway. It was also found that these mutants had elevated rcsB activity levels only when stressed with high concentrations of antibiotic. rcsA was also deleted in these mutants to see if production of colanic acid affects resistance levels. Upon rcsA deletion, the mutants did not experience a decrease in resistance, indicating rcsA was not required for resistance.