Frédérique Le Roux : Understanding Bacteria’s Natural Enemies

Meet Frédérique Le Roux, IVADO Professor and Full Professor in the Department of Microbiology, Infectiology and Immunology at Université de Montréal. 

Frédérique Le Roux sees antibiotic resistance as one of the most pressing threats facing modern medicine. A toothache that spreads to the brain, or an infection on a prosthesis that no available treatment can clear: without alternatives, these common situations could become as deadly as cancer. This challenge shapes her entire research program. 

Professor Le Roux, who holds the Canada Excellence Research Chair dedicated to the ecology, evolution and virulence of microbes in nature, studies vibrios, aquatic bacteria that cause disease in animals such as oysters and shrimp.

Some species can also cause serious illness in humans. She is particularly interested in the relationship between these bacteria and their natural predators: bacteriophages, viruses that infect and kill bacteria. Inside an oyster, this dynamic never ends: bacteriophages reduce bacterial populations, bacteria develop resistance mechanisms, the phages adapt in turn, and so on. She describes this as coevolution through an arms race. 

Nature has regulated this balance on its own for millennia, and Professor Le Roux studies it in the field. She observes what happens in coastal waters, environments subject to the vagaries of the seasons. Her laboratory has built a unique collection of environmental isolates: bacteria and phages sampled over several years from the same sites.

In 2017, her team collected samples at an oyster farm in Brittany. Returning four years later, she found the same phages and the same bacteria. It was an unexpected result, one that challenges the idea that bacteriophages necessarily evolve rapidly and unpredictably in nature. 

Her team then analyzes these samples, using computational tools to compare genomes and identify how bacteria and phages defend themselves and adapt to one another. The long-term goal is to predict which phages will be effective against resistant bacteria, information that is critical to the development of phage therapy.

Algorithmic tools and AI play a growing role in this work. “Our job, essentially, is to feed AI,” she says, noting that every new resistance or counter-resistance gene identified helps refine prediction systems. 

Her approach is grounded in the One Health framework, which recognizes the interdependence of human, animal and environmental health. Pathogenic vibrios have immune defences and coevolve with their phages. The same types of mechanisms are found in bacteria that infect humans.

She draws a parallel: an oyster is efficiently infected by a vibrio only when a herpesvirus weakens its immune system, much as an immunocompromised patient can develop an opportunistic bacterial infection. Vibrios therefore serve as models: more accessible from an ethical standpoint, easier to handle in the laboratory, yet representative of universal biological phenomena. 

After earning her PhD at the Université de Lyon, Frédérique Le Roux worked at several institutions before leading a team specializing in vibrio genomics for thirteen years at the Roscoff Biological Station in France.

She moved to Montréal in 2023, drawn by the opportunity to collaborate with specialists in molecular genetics and microscopy, notably in the department where Yves Brun, Canada 150 Research Chair in Bacterial Cell Biology, also teaches.

She is also interested in the effects of climate warming on vibrio communities, a phenomenon she plans to study in the Canadian context, where these dynamics remain poorly documented. One conviction has guided her from the start: “Nature regulates things very well on its own. My job is to try to understand how.”