New research from NC State highlights that probiotic effects are strain-specific and highly situational.More studies are needed to fully understand how individual probiotic strains impact the gut microbiota. People often take probiotics after antibiotics to prevent C. difficile-related diarrhea. However how each strain interacts with the gut environment remains unclear. The study examined how quickly the gut regained resistance to C. diff after antibiotic use. Researchers tested two popular Lactobacillus strains to observe their influence on this recovery. The study involved three groups of mice treated with cefoperazone a common broad-spectrum antibiotic. One group received no probiotics while the other two were given either Lactobacillus acidophilus or Lactobacillus gasseri. All groups were exposed to C. difficile weekly for four weeks and researchers monitored bacterial load and resistance. Mice without probiotics regained resistance and showed reduced bacterial load by week four.
In contrast the L. acidophilus group showed higher bacterial loads in weeks two and three while the L. gasseri group showed no detectable C. diff after just two weeks. Interestingly L. gasseri didn’t colonize the gut but promoted beneficial bacteriocins and supported the growth of Muribaculaceae a potentially helpful microbe.

We’ve always known that the effects of probiotics depend on the specific strain says Rodolphe Barrangou Todd R. Klaenhammer Distinguished Professor at NC State and co-corresponding author. Factors like a person’s microbiome the illness involved and the probiotic strain all contribute to varying outcomes.

He adds This study reveals just how complex the interaction is probiotics may have only short-term or indirect effects. For example L. gasseri doesn’t directly prevent infection but seems to aid microbiome recovery by supporting Muribaculaceae which may later enhance resistance. That insight points us in exciting new directions.

This is the first study to functionally test microbiome resistance adds co-author Casey Theriot. Though it’s based on a mouse model the findings highlight the urgent need for a deeper mechanistic understanding. Some probiotics can influence the microbiome long after they're gone and in some cases may actually delay or complicate recovery.

Source: https://news.ncsu.edu/2025/07/probiotics-can-help-or-hinder-gut-recovery-after-antibiotic-treatment/