Bacterial Responses to Antibiotic-induced Stresses

Open Access
Kilmer, Michelle Renee
Area of Honors:
Biochemistry and Molecular Biology
Bachelor of Science
Document Type:
Thesis Supervisors:
  • Sarah Ellen Ades, Thesis Supervisor
  • Sarah Ellen Ades, Honors Advisor
  • Kenneth Charles Keiler, Faculty Reader
  • Scott Brian Selleck, Faculty Reader
  • Antibiotic Resistance
  • Ecological Theory
  • Cell Envelope Stress Response Pathways
  • Rcs phosphorelay
  • Ecological Factors
Understanding how bacteria respond to a stressful environment can be beneficial when studying antibiotic resistance. The knowledge gained can suggest methods to reduce the amount of resistance that arises in the future. This thesis focuses on two approaches for exploring how bacteria respond to an antibiotic-induced stressful environment. The first studies the importance of the Rcs phosphorelay, a cell envelope stress response pathway in E. coli, and how it contributes to resistance. We monitored how the deletion of various components of the pathway affects contribution of the response to resistance. The second is an ecological approach, where factors related to antibiotic treatment were manipulated and the outcome of the response was monitored. The first method was accomplished by selectively deleting components of the Rcs phosphorelay and observing the difference in the number of colonies that grew when added to ampicillin. Upon deletion of each component, partial dependence on the pathway was observed, as there was a decrease but not a complete reduction in the number of colonies. The most dependence was on the RcsF component when plated on solid medium and the RcsB component in liquid medium. The second method involved manipulation of three ecological factors: timing, intensity, and frequency. We varied the amount of antibiotic added, when the antibiotic was added with respect to the growth curve, and the number of times the antibiotic was added. It was it was determined that timing is most the important factor. The results showed that the addition of amp at the beginning of the growth curve is more effective compared to the middle or end. Additionally, the data reflected that higher intensities of 15 and 20 μg/ml amp given in split amounts across the growth curve was equivalent to smaller intensities of 5 and 10 μg/ml given all at once. This suggests a possible correlation between intensity and frequency.