When 10-year-old John Nixon's cancer tumors suddenly shrank in 1891, his doctors were baffled. The boy had developed a severe bacterial infection — and somehow, that infection was fighting his cancer. The physician watching this unfold was William Coley of New York, and what he witnessed would launch one of the strangest chapters in cancer medicine.
More than 130 years later, scientists at the University of Waterloo are reviving Coley's radical idea — but with a modern twist. They are engineering bacteria to hunt down and destroy tumors from the inside, and early results are generating real excitement.
The strategy relies on a clever biological quirk. Cancer tumors grow so fast that their blood supply becomes chaotic and inefficient. This creates pockets inside the tumor where oxygen levels are very low. Meanwhile, healthy tissues stay richly supplied with oxygen. Certain bacteria happen to thrive exactly in those low-oxygen spaces — they can't survive where oxygen is plentiful.
"These so-called anaerobes are generally unable to infect healthy tissues, where oxygen is abundant," explains the Waterloo research team, which includes alumni Bahram Zargar and Sara Sadr from the university's Department of Chemical Engineering. "But the low-oxygen environment provides a unique niche for an anaerobic bacterial infection."
The team is working with a bacterium called Clostridium sporogenes — a harmless soil microbe related to the bacteria that cause tetanus and produce Botox. Injected into a patient, dormant spores of this bacterium would travel harmlessly through the bloodstream, staying inactive in healthy tissue. But once they slip inside a tumor's oxygen-poor core, the spores wake up and begin multiplying, attacking the tumor from within.
This idea is not entirely new. In the mid-20th century, researchers tested C. sporogenes injections in cancer patients and saw some tumor shrinkage. But the effect was short-lived. The bacteria damaged the tumor's interior but couldn't reach its outer edges, which had enough oxygen to keep growing.
That is where modern genetic engineering changes the equation. The Waterloo team is using tools from synthetic biology — a field focused on redesigning living organisms for specific tasks — to build smarter versions of C. sporogenes that could overcome these limitations. The goal is bacteria that can more completely suppress tumors, without harming the patient.
Coley's original experiments were risky: about one-third of his patients improved, but roughly 5% died from the infections themselves. Modern controlled laboratory work aims to capture the cancer-fighting benefit while eliminating the danger. If the approach proves safe and effective, it could offer a new weapon against tumors that resist conventional treatments.
The path from petri dish to patient is long, but researchers see clear reasons for optimism. Bacteria have been fighting cancers in nature for longer than medicine has existed. Now, scientists are simply learning to direct the battle.