Specific gut microbe makes sepsis deadlier in mice

11.09.2026

Sangeribacter muris KT1-3 made sepsis deadlier by amplifying inflammation driven by TLR4.

What is already known

Gut bacteria help train the immune system, and disrupted microbial communities have been linked to worse infections and sepsis. Whether specific gut bacteria can prime the body for inflammation is unclear, but scientists suspect that TLR4, an immune sensor that detects Gram-negative bacterial molecules, can trigger the production of large amounts of inflammatory molecules called cytokines.

What this research adds

Researchers tested why genetically similar mice had different survival rates after infection with Acinetobacter baumannii, a bacterium that can cause severe sepsis. Mice with gut microbiotas rich in a bacterium called Sangeribacter muris KT1-3 were more likely to die. Further experiments showed that the bacterium primes specific immune cells called macrophages to overreact. In mice, S. muris KT1-3 made sepsis deadlier by amplifying inflammation driven by TLR4.

Conclusions

The findings suggest that sepsis risk may depend partly on a person’s pre-existing gut microbiota, raising the possibility of targeting specific microbes to reduce dangerous inflammation.

Gut bacteria help train the immune system, and disrupted microbial communities have been linked to worse infections and sepsis. Now, a study done in mice shows that a specific gut bacterium can make sepsis deadlier by priming the immune system to overreact.

The findings, published in Nature Communications, suggest that sepsis risk may depend partly on a person’s pre-existing gut microbiota, raising the possibility of targeting specific microbes to reduce dangerous inflammation.

Whether specific gut bacteria can prime the body for inflammation was unclear, but scientists suspected that TLR4, an immune sensor that detects Gram-negative bacterial molecules, can trigger the production of large amounts of inflammatory molecules called cytokines.

So, researchers led by Seonghan Jang at the Korea Research Institute of Bioscience & BioTechnology in Daejeon tested why genetically similar mice had different survival rates after infection with Acinetobacter baumannii, a bacterium that can cause severe sepsis.

Inflammatory molecules

After being infected with A. baumannii, mice surviving longer had more bacteria such as Lactobacillaceae and Bacteroidaceae, whereas more vulnerable animals had high levels of Muribaculaceae.

When the researchers isolated Muribaculaceae strains, only one—Sangeribacter muris KT1-3—increased mortality, showing that the dangerous effect was strain-specific.

Early after infection, bacterial levels were similar between resistant and susceptible mice, but the susceptible mice showed much higher levels of cytokines. Later, they also showed higher bacterial levels in blood and organs.

Overreactive cells

Next, the researchers transferred gut microbes between resistant and susceptible mice after antibiotic treatment. Mice that received the resistant-type microbiota survived better and had lower bacterial levels, whereas mice that received the susceptible-type microbiota became more vulnerable. Similar patterns were observed after co-housing resistant and susceptible mice.

Further experiments showed that S. muris KT1-3 primes specific immune cells called macrophages to overreact. In mice, the bacterium made sepsis deadlier by amplifying inflammation driven by TLR4, the researchers found.

Although it’s unclear which molecules drive this effect and whether the same mechanism matters in humans, the authors say their findings “reveal a microbiota–TLR4 axis that links specific commensal bacteria to systemic hyperinflammation and provide a conceptual framework for understanding how gut microbes modulate the pathogenesis of sepsis.”