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Not an easy question to answer. Research on a probiotic like Lactobacillus rhamnosus centers around its capability to outcompete and/or kill pathogenic bacteria such as E. coli O157, Salmonella sp., Listeria sp., etc. Thus, experimental systems using it are designed to see if it/its products outcompete and/or kill, and not the other way around. Confirmation bias? For sure. It also made finding relevant data akin to looking for the proverbial needle in a haystack.

First, a preamble to explain the importance of Lactobacillus rhamnosus.

  • Lactobacillus species are among the earliest colonizers of human GI (gastro-intestinal) tract, reaching peak numbers by about 6 months of age (1).
  • Most common species are Lactobacillus rhamnosus and Lactobacillus gasseri (2, 3).
  • Lactobacillus rhamnosus, L. plantarum, L. paracasei, Bifidobacterium bifidum and B. lactis are the most commonly used bacteria in commercial probiotics.
  • At this point a definition of probiotic would be handy. In 2001, the FAO (Food and Agriculture Organization) and the WHO defined probiotics as ‘Live microorganisms which when administered in adequate amount confer a health benefit to the host‘ (4).
  • The International Scientific Association for Probiotics and Prebiotics (ISAPP) accepts the same definition.
  • The EFSA (European Food Safety Authority) and the US FDA currently do not accept this definition (5).
  • For EFSA and the FDA, the probiotic definition is not measurable as science has not kept pace with the ability to substantiate the ‘health benefits‘ claim of commercial probiotics.

There are numerous L. rhamnosus strains. At least 6 are commonly used in most commercial probiotics (6).

L. rhamnosus GG, [ATCC (American Type Culture Collection) 53103] is among the most widely used probiotic (7).

  • Isolated from healthy human adult fecal sample by Sherwood Gorbach and Barry Goldwin.
  • Hence the strain name GG.
  • Resistant to acid and bile.
  • Adheres to gut intestinal epithelium.

Comparative studies of L. rhamnosus strains are recent and suggest considerable dissimilarities among them (8).

Specifically, in a 2013 study (8), dairy isolates were less effective against pathogenic E. coli and Listeria monocytogenes strains.

  • Again, this experiment points to the difficulties in answering whether something outcompetes or kills L. rhamnosus (or indeed any probiotic). Why so?
  • They cultured L. rhamnosus and harvested its culture supernatants.
  • Then they cultured the pathogens in presence/absence of these L. rhamnosus culture supernatants.

However, in a direct comparison in the same study, dairy-derived L. rhamnosus were more susceptible to bile acids.

A 2014 study (10) compared 184 strains of Lactobacilli.

  • Found L. rhamnosus selectively susceptible in vitro to certain types of oxidative stress.
  • Specifically susceptible to oxidative stress induced by hydrogen peroxide (H2O2) and Menadione.
  • Resistant to oxidative stress induced by Pyrogallol.


  1. Adlerberth I, Lindberg E, Aberg N, Hesselmar B, Saalman R, Strannegård I, Wold A (2010) Reduced enterobacterial and increased staphylococcal colonization of the infantile bowel: an effect of hygienic lifestyle? Pediatr Res 59(1):96–101.
  2. Ahrne S, Lonnermark E, Wold AE, Aberg N, Hesselmar B, Saalman R, Strannegard IL, Molin G, Adlerberth I (2005) Lactobacilli in the intestinal microbiota of Swedish infants. Microb Infect 7(11–12):1256–1262.
  3. Mitsou EK, Kirtzalidou E, Oikonomou I, Liosis G, Kyriacou A (2008) Faecal microflora of Greek healthy neonates. Anaerobe 14(2):94–101.
  4. FAO/WHO (2001) Health and nutritional properties of probiotics in food including powder milk with live lactic acid bacteria. Report of a Joint FAO/WHO expert consultation on evaluation of health and nutritional properties of probiotics in food including powder milk with live lactic acid bacteria.
  5. Page on ec.europa.eu
  6. Chapter 2. The Intestinal Microbiota and Probiotics. Page 48. Sofia D. Forssten, Sampo J. Lahtinen, Arthur C. Ouwehand. Probiotic Bacteria and Enteric Infections. Malago, Joshua J., Jos FJG Koninkx, and Romana Marinšek-Logar. Springer Dordrecht Heideberg London New York, 2011. http://dlib.bpums.ac.ir/multiMed…
  7. Doron, Shira, David R. Snydman, and Sherwood L. Gorbach. “Lactobacillus GG: bacteriology and clinical applications.” Gastroenterology Clinics of North America 34.3 (2005): 483-498.
  8. Kant, Ravi, et al. “A comparative pan-genome perspective of niche-adaptable cell-surface protein phenotypes in Lactobacillus rhamnosus.” PloS one 9.7 (2014): e102762. Page on plos.org id=10.1371/journal.pone.0102762#pone-0102762-g004
  9. Douillard, François P., et al. “Comparative genomic and functional analysis of 100 Lactobacillus rhamnosus strains and their comparison with strain GG.” PLoS genetics 9.8 (2013): e1003683. Comparative Genomic and Functional Analysis of 100  Lactobacillus rhamnosus  Strains and Their Comparison with Strain GG
  10. Zotta, Teresa, et al. “Assessment of aerobic and respiratory growth in the Lactobacillus casei group.” PLOS one 9.6 (2014): e99189. Page on plosone.org uri=info:doi/10.1371/journal.pone.0099189&representation=PDF