Karen Maxwell

Karen Maxwell is a Professor in the Department of Biochemistry at the University of Toronto, where she holds a Tier 1 Canada Research Chair in Bacteriophage Biology and Therapeutics. She received her B.Sc. in Biochemistry from the University of Waterloo, her Ph.D. in Molecular Genetics from the University of Toronto, and conducted postdoctoral research at the Ontario Centre for Structural Genomics. Prior to her faculty appointment, Dr. Maxwell held a senior research associate position at the Terrence Donnelly Centre for Cellular and Biomolecular Research.

Dr. Maxwell’s research program focuses on the interactions between bacteria and the viruses that infect them, known as phages. Her laboratory investigates how phages recognize and enter bacterial cells, how bacteria detect and block infection, and how some phages overcome these defences. By integrating genetics, biochemistry, and genome-based approaches, her team identifies the proteins and pathways that determine whether infection succeeds or fails. A central goal of Dr. Maxwell’s program is to translate fundamental discoveries into practical applications. Insights from her lab have supported the development of new tools for studying virus–host interactions and have advanced efforts to harness phages in biotechnology and as therapeutics for antibiotic-resistant bacterial infections. Dr. Maxwell’s contributions have been recognized with honours including the Natural Sciences and Engineering Research Council of Canada Arthur B. McDonald Fellowship and the John C. Polanyi Award.

The Work:

Karen Maxwell studies how bacteria defend themselves against viruses known as bacteriophages, and how the viruses evolve to bypass these bacterial immune systems. Her research integrates genetics, biochemistry, and structural biology to uncover sophisticated molecular strategies. 

Dr. Maxwell’s research group has discovered and characterized multiple new bacterial immune systems and the mechanisms that regulate when these systems turn on during infection. This work helps us understand exactly how bacterial immunity works and how these defences are deployed at the right time. Among Dr. Maxwell’s key discoveries is that some bacteria produce small chemical compounds that block viral replication as a form of “chemical immunity.”  

Her work also shows that bacterial immunity is shaped by genes carried on mobile pieces of DNA, including viral DNA left behind in bacterial genomes. These dormant viral elements can actively protect their hosts by detecting invading viruses and triggering rapid immune responses. Together, these studies have reshaped the scientific framework for understanding microbial immunity and virus–host interactions.

The Impact:

Antibiotic resistant bacterial infections are a major global health challenge, threatening millions of lives each year. The work of Dr. Maxwell has transformed how scientists understand the battle between bacteria and the viruses that infect them. Her discoveries revealed new bacterial defence strategies and the ways phages bypass them, providing a foundation for designing precise, next-generation phage-based therapies. 

These insights are already guiding the development of treatments that can target harmful bacteria while preserving beneficial microbes, and they are informing genome-editing technologies and synthetic biology applications. By mapping the strategies of both bacteria and phages, Dr. Maxwell’s research is opening new paths for fighting infections, managing antibiotic resistance, and advancing biotechnology, with broad benefits for human health.