Probiotics Are Good for You-Except When They’re Not

The penultimate sentence in a recent research letter in Nature Medicine captures what most people have heard about probiotics: “Probiotics have shown significant benefits for acute infectious diarrhea, antibiotic-associated diarrhea, and ulcerative colitis.” But it’s the last sentence in the letter that garnered headlines like this today-“When 'Friendly' Probiotic Bacteria Turn Into Foes In The ICU.” 

In that last sentence, investigators at Boston Children’s Hospital write that “our findings highlight that as ICU patients have increased risk for probiotic-associated bacteremia, these potential benefits must be weighed against this risk when considering the continued use of probiotics in the ICU.”

The risks are substantial, too, according to investigators: ICU patients on probiotics are 120 times more likely to develop Lactobacillus bacteremia, a bloodstream infection. 

Some strains ofLactobacillus-such as Lactobacillus rhamnosus-are what make probiotics a health enhancer, for the most part. However, the research letter states that Lactobacillus rhamnosus can morph into Lactobacillus bacteremia. Investigators did this by collecting “genomics data that support the idea of direct clonal transmission of probiotics to the bloodstream.” 

Then it becomes a superbug, resistant to most antibiotics. “Our findings support that probiotic strains can directly cause bacteremia and adaptively evolve within ICU patients,” the research letter states.

Greg Priebe, MD, one of the authors of the research letter, told WBUR, the public radio station in Boston, that Boston Children’s Hospital eventually banned probiotics in 2017 for ICU patients who are being treated intravenously. 

An epidemiological analysis was conducted over 5 yearsof 22,174 patients who were treated in an ICU, and 522 of those patients received the Lactobacillus rhamnosus strain GG (LGG) probiotics-typically through a feeding tube-as part of their treatment. Investigators found that 6 of the 522 patients had Lactobacillus bacteremia compared with only 2 of the 21,652 patients who did not receive the LGG probiotic.

The research letter calls for more studies to be done on this matter. A huge international study is now underway that seeks to weigh the risks against the benefits of probiotics in the ICU.