Intended for healthcare professionals


Safety of probiotics: comparison of two popular strains

BMJ 2006; 333 doi: (Published 09 November 2006) Cite this as: BMJ 2006;333:1006
  1. Cathy Hammerman, director of newborn nursery1,
  2. Alona Bin-Nun, neonatal fellow2,
  3. Michael Kaplan, chairman of neonatology1
  1. 1Department of Neonatology, PO Box 3235, Shaare Zedek Medical Centre, Jerusalem, Israel 91031
  2. 2Department of Neonatology, University of Chicago Medical Center, Chicago, IL, USA
  1. Correspondence to: C Hammerman cathy{at}
  • Accepted 17 October 2006

Summary points

  • Lactobacilli and bifidobacteria are ubiquitous in the human diet and healthy intestine, and systemic infections with these bacteria may occur naturally, unrelated to ingestion of probiotics

  • Sepsis due to Lactobacillus has not been reported in prospective randomised studies of probiotics

  • The risk of sepsis due to Lactobacillus should be weighed against that of sepsis with more pathological species of bacteria and against that of the disease which probiotic therapy is meant to prevent (such as necrotising enterocolitis)

  • Most reported cases of bacteraemia or sepsis have been secondary to Lactobacillus rhamnosus GG or Lactobacillus casei

  • Different strains of probiotics have different safety profiles, which should be taken into account. Systemic infection has rarely been reported with Bifidobacterium

Mounting clinical evidence shows that nutritional supplements of live micro-organisms (probiotics) have health advantages to humans. The appeal of probiotic therapy lies in the fact that it not only represents a non-invasive attempt to recreate natural flora rather than a disruption of nature, but it is also an approach that is both cheap and effective.

However, the concept of willingly ingesting live bacteria remains somewhat counterintuitive. Although probiotic therapy is generally considered harmless, rare reports of systemic infections involving probiotic bacteria have raised clinical concerns. We therefore conducted a scientific review of the safety of these organisms. For the purpose of this review, we assumed therapeutic effectiveness and concentrated primarily on evaluating the safety of this treatment. Although many such reviews exist, previous authors have taken a uniform approach—they have mostly reported anecdotal case reports of infection or infection rates with the strain under investigation and then generalised their findings to all probiotics. We have tried to isolate the different safety profiles of diverse probiotic strains.


The human intestine is home to more than a trillion live bacteria from about 400 species. The average …

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