Gut-dwelling bacteria produce molecules that could reveal who is prone to a life-threatening consequence of antibiotic treatment.

The discovery that active infection by the opportunistic bacterium Clostridioides difficile is accompanied by a distinct molecular signature could lead to swifter diagnosis.

Antibiotics can change the make-up of an individual’s gut microbes — collectively known as the microbiome — allowing C. difficile to overgrow and trigger diarrhoea, and in some cases severe, life-threatening gut inflammation. But not all those who carry the bacterium develop the disease.

To identify a telltale sign of C. difficile, Jeffrey Henderson at Washington University School of Medicine in St Louis, Missouri, and his colleagues analysed the molecules produced by the microbiomes of 186 people who had been hospitalized with diarrhoea, some of whom had C. difficile infection and some of whom did not.

In the stools of those with C. difficile infection, the team found high levels of 4-methylpentanoic acid, a molecule produced when C. difficile breaks amino acids down for fuel. The researchers also identified a series of modified bile acids that were present in much lower levels in people with C. difficile infection than in those who either did not carry the bacterium or carried it without showing symptoms.

Together, these molecular signatures could help scientists to identify and prevent C. difficile infection, the researchers say.