That message matters for clinical practice. When hospitals find B. cereus in a wound sample, staff may assume the bacterium simply drifted in from the environment and ignore it. The new results suggest that assumption can be wrong.

Acidity turned out to be decisive

The study's most surprising finding concerned pH, the scale that measures how acidic or alkaline a solution is. The toxin's harmful activity was significantly lower under acidic conditions than at neutral or alkaline pH levels.

This detail matters because of what chronic wounds are actually like. Blood, tissue fluids and metabolic byproducts such as ammonia can push a chronic wound toward a more alkaline environment. Those conditions, the researchers suggest, may favor bacterial growth and colonization — effectively turning the wound into a comfortable base for the bacterium.

The result also carries a broader lesson about how bacteria cause disease. The same research group previously showed that a different toxin, MakA, produced by the cholera bacterium Vibrio cholerae, switches on under acidic conditions. NheABC behaves in exactly the opposite way, showing maximum activity when acidity drops.

In other words, toxins are not weapons that fire identically in every setting. Their power depends on where the bacterium finds itself.

"If toxin activity depends on the surrounding environment, this could open up new ways of reducing tissue damage during infections. In the future, it may be possible to target the wound environment itself, rather than focusing solely on the bacterium," says Aftab Nadeem, a researcher at the Department of Molecular Biology at Umeå University and senior author of the study.

From cell cultures to living tissue

The findings rest on a wide range of experimental models, which strengthens confidence in the results. The team worked with human cells grown in both two- and three-dimensional systems, laboratory-grown mini-guts known as intestinal organoids, artificial cell membranes and advanced microscopy. To test whether the toxin matters in a real infection, they also used a mouse model of wound infection.

In that mouse model, NheABC contributed to increased bacterial colonization of the wound and triggered a stronger local inflammatory response — the immune system's reaction to infection, which itself can add to tissue damage.

Still, the results come largely from laboratory models and animals, and they do not yet show how the findings translate to human patients with chronic wounds. Whether adjusting the wound environment — for example its pH — can meaningfully reduce tissue damage remains a question for future research.

The study was carried out in collaboration between researchers at Umeå University, the Norwegian University of Life Sciences and Lund University. The paper appears as Naeem Ullah et al., "NheABC is a pH-dependent cytotoxin that targets mitochondria and contributes to the virulence of Bacillus cereus in wound infections" (Cell Communication and Signaling, 2026; DOI: 10.1186/s12964-026-03235-x).