Antibiotic resistance, antibiotic tolerance and the stringent response
| dc.contributor.author | Deventer, Ashley | |
| dc.contributor.supervisor | Hobbs, Joanne K. | |
| dc.contributor.supervisor | Boraston, Alisdair B. | |
| dc.date.accessioned | 2023-08-22T20:27:12Z | |
| dc.date.copyright | 2023 | en_US |
| dc.date.issued | 2023-08-22 | |
| dc.degree.department | Department of Biochemistry and Microbiology | |
| dc.degree.level | Master of Science M.Sc. | en_US |
| dc.description.abstract | Bacterial infections are a major global cause of mortality, and antibiotics are critical to their treatment. However, effective antibiotic therapy is threatened by antibiotic resistance and antibiotic tolerance. Tolerance is distinct from resistance as tolerant bacteria are still susceptible to antibiotics, but the rate of killing is significantly reduced. While resistance is a well-understood antibiotic evasion strategy, tolerance is an underappreciated bacterial phenomenon that greatly impacts treatment outcomes. Unlike resistance (which is identified by routine testing in laboratories), tolerance is not tested for in clinical laboratories, in part because there is no simple test available. Consequently, the clinical prevalence and significance of tolerance is unknown. Recently, the stringent response (SR) has emerged as a clinically-relevant mechanism implicated in both resistance and tolerance. The SR is a universal bacterial stress response that acts as a master regulator of bacterial physiology and virulence. In most bacteria, activation of the SR is controlled by the protein Rel. In this study, the SR was used as a model system in Staphylococcus aureus to better understand the wider consequences of SR-activating mutations for antibiotic therapy, and the magnitude of the problem of tolerance. Here, I demonstrate that SR activation promotes conjugal transfer of multidrug resistance plasmids between strains of S. aureus via elevated plasmid copy number. SR activation increased the transmission of plasmids from diverse families, suggesting that the SR plays a significant role in the dissemination of resistance. SR-activated mutants were also used in the development and validation of a simple screen to detect genotypic tolerance. This screen uses ATP as a proxy for viability and eliminates the need for enumeration of colony-forming units. In a pilot study, I applied the screen to a library of 39 S. aureus isolates from cystic fibrosis lung infections and detected tolerance in 8% of isolates. This study demonstrates that, while Rel mutations may arise during infection and confer tolerance, they have a secondary, coincidental consequence of promoting the dissemination of multidrug resistance plasmids. Furthermore, it demonstrates that the SR is a useful and much-needed model system for studying antibiotic evasion strategies in general. Ultimately, this study highlights the multifaceted implications of clinical Rel mutations and demonstrates that SR activation has significant consequences for antibiotic therapy. | en_US |
| dc.description.scholarlevel | Graduate | en_US |
| dc.identifier.uri | http://hdl.handle.net/1828/15278 | |
| dc.language | English | eng |
| dc.language.iso | en | en_US |
| dc.rights | Available to the World Wide Web | en_US |
| dc.subject | Antibiotic resistance | en_US |
| dc.subject | Antibiotic tolerance | en_US |
| dc.subject | Stringent response | en_US |
| dc.subject | Staphylococcus aureus | en_US |
| dc.subject | Conjugation | en_US |
| dc.subject | Plasmid | en_US |
| dc.title | Antibiotic resistance, antibiotic tolerance and the stringent response | en_US |
| dc.type | Thesis | en_US |