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Contact Details

Email
rachel.darnell@otago.ac.nz

University Links

Position
Research Fellow
Department
Department of Microbiology and Immunology
Research summary
Clinical and molecular microbiology; Antimicrobial resistance; Antimicrobial tolerance

Research

Understanding mechanisms of antimicrobial tolerance in the bacterial pathogen Enterococcus faecalis

Enterococci are intrinsically tolerant to a number of antimicrobials including vancomycin and the recently discovered antimicrobial teixobactin. We have previously identified the two-component regulatory system CroRS as essential for antimicrobial tolerance in Enterococcus faecalis. What we are now interested in understanding is what genes CroRS regulates to confer this tolerance and the molecular mechanisms of this tolerance. In addition, we are developing a pipeline to carry out genome-wide association analyses of enterococcal genomes to identify novel factors of antimicrobial tolerance.

Targeting antimicrobial tolerance in the bacterial pathogen Enterococcus faecalis

Antimicrobial tolerance is known to precede the development of antimicrobial resistance. In addition, antimicrobial tolerance increases the risk of treatment failure, particularly in the immunocompromised. Our aim is to identify inhibitors of antimicrobial tolerance that will work synergistically with current antimicrobials to reduce the development and spread of antimicrobial resistance.

Determining the role of Type I phase-variable restriction modification systems in enterococci

We have identified a number of Type I phase-variable restriction modification systems in enterococci. Now we are investigating the role and regulation of these phase-variable systems in both Enterococcus faecalis and Enterococcus faecium.

Publications

Darnell, R. L., Knottenbelt, M. K., Rose, O. E., Cleary, C. S. B., Todd Rose, F. O., Hodgkinson, H., … Cook, G. M. (2025). Prolonged exposure to teixobactin generates cross-tolerance to other cell wall-targeting antimicrobials in Enterococcus faecalis. Antimicrobial Agents & Chemotherapy. Advance online publication. doi: 10.1128/aac.00629-25 Journal - Research Article

Paxie, O., Darnell, R., Todd Rose, F., Chueng, C.-Y., & Cook, G. (2023). Understanding the functional role of respiratory oxidase enzymes in the bacterial pathogen Enterococcus faecalis. Proceedings of the New Zealand Society for Biochemistry and Molecular Biology (NZSBMB) 50th Anniversary Conference. Retrieved from https://www.nzsbmb.org/conference Conference Contribution - Published proceedings: Abstract

Todd Rose, F. O., Darnell, R. L., Morris, S. M., Rose, O. E., Paxie, O., Campbell, G., Cook, G. M., & Gebhard, S. (2023). The two-component system CroRS acts as a master regulator of cell envelope homeostasis to confer antimicrobial tolerance in the bacterial pathogen Enterococcus faecalis. Molecular Microbiology, 120, 408-424. doi: 10.1111/mmi.15128 Journal - Research Article

Paxie, O., Todd Rose, F., Cheung, J., Cook, G., & Darnell, R. (2022, August). Investigating the functional role respiratory oxidases play in the bacterial pathogen Enterococcus faecalis. Poster session presented at the Webster Centre for Infectious Diseases Satellite Meeting: Queenstown Research Week, Queenstown, New Zealand. Conference Contribution - Poster Presentation (not in published proceedings)

Smith, M. J. B., Cheung, C. Y., Cook, G. M., & Darnell, R. L. (2022, August). Investigation of antimicrobial tolerance in Enterococcus faecalis. Poster session presented at the Webster Centre for Infectious Diseases Satellite Meeting: Queenstown Research Week, Queenstown, New Zealand. Conference Contribution - Poster Presentation (not in published proceedings)

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