A study in the US has found that not all probiotic bacteria are beneficial after antibiotic treatment, with some types of probiotics potentially worsening gut infections in mice.

Probiotics are commonly taken after antibiotic treatment to help restore gut balance and reduce the risk of antibiotic-associated diarrhoea caused by Clostridioides difficile. However, the impact of these bacteria on gut recovery is not fully understood.

Researchers at North Carolina State University (NC State) tested two commonly used probiotic microbes — Lactobacillus acidophilus and L. gasseri — in mice that were previously treated with a common antibiotic, cefoperazone. After infection with C. difficile, mice that received L. acidophilus were more susceptible to infection, while those given L. gasseri were better protected.

The team discovered that L. gasseri carries extra antibacterial genes that could directly fight C. difficile. It also promoted the growth of Muribaculaceae, a group of gut bacteria that eats the same nutrients as C. difficile, thus contributing to its starvation. By contrast, L. acidophilus may inadvertently feed the pathogen by providing nutrients that C. difficile needs to grow. 

“Although this work is in a mouse model, it shows the need for better mechanistic understanding of how probiotics affect the microbiome,” said Casey Theriot, co-leader at NC State of the study published in mBio. “Not only can they have effects weeks after they’ve left the body, in certain situations they have the potential to prolong or complicate recovery.”