Editors' ChoiceBACTEREMIA

Probiotics leap from gut to blood

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Science Translational Medicine  04 Dec 2019:
Vol. 11, Issue 521, eaaz9763
DOI: 10.1126/scitranslmed.aaz9763

Abstract

In critically ill patients, probiotics are associated with probiotic strain bacteremia and can evolve in response to antibiotic administration.

The gut microbiome has been associated with health and disease states. As antibiotics can upset gut homeostasis, probiotics are increasingly used to restore a beneficial microbiome, particularly in critically ill patients. Probiotics have shown benefit in infectious or antibiotic-related diarrhea, and ongoing studies are exploring their use for other conditions. However, there are concerns that the probiotic bacteria may translocate into the bloodstream, resulting in bacteremia and sepsis. As the bacteria within probiotics are commonly found in the human gut microbiome, it has been difficult to identify the source of bacteremia, particularly with strain-level tests that do not sequence whole genomes.

To address these issues, Yelin et al. examined the rates of Lactobacillus bacteremia among ICU patients at Boston Children’s Hospital and found that patients receiving Lactobacillus rhamnosus strain GG (LGG) probiotics had an overall low, but comparatively higher, rate of Lactobacillus bacteremia (1.1%) than those not receiving probiotics (0.009%). To determine if the bacteria in blood was derived from the LGG probiotics, the authors performed whole-genome sequencing of both blood isolates and the LGG probiotic strain. They found several mutations from blood Lactobacillus that were also identified in the probiotic bacteria, suggesting that translocation had likely occurred from the gut to blood. They also identified several de novo mutations from blood isolates not present in the capsules, suggesting selective host pressure had induced these changes. Importantly, one blood isolate had a new mutation conferring rifampin resistance, an antibiotic that patient had received concurrently.

This work strongly highlights the potential for probiotics to have unintended and possibly harmful effects. Although all patients with LGG bacteremia eventually recovered with antibiotics, these events further complicated the clinical picture of already critically ill patients. Further epidemiologic- and sequence-based studies will be necessary to determine how these de novo mutations occur and to identify specific factors that lead to the increased risk of bacteremia to better define the risk-benefit profile of probiotic administration in the ICU.

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