When you look at different strains of a probiotic such as Lactobacillus Reuteri and dig far enough into research papers — you will see charts like the one below.

All strains of a Species are not created equal

As shown above: some produce histamine, some produces folate and produce high amount of Reuterin (the natural antibiotic against infections). For many people, the ideal Lactobacillus Reuteri probiotic would be a folate producer, with no histamine and hgh Reuterin production. This excludes the fact that we also should care about the source.

Interspecies Probiotics do not take up residency

If you look at the above chart, and look at history: all of these creatures have co-existed with mankind (and each other) for millenium. It appears that some strains may be shared between chickens and humans – it’s unusual. There are very few common strain between any of them. We know bacteria gets transferred by a kiss (see this post Kisses, Sex and FM/CFS/IBS ) and some intake of bacteria from these creatures would occur in the farm yard…. but rarely have any taken up residency in humans.

After oral consumption of probiotics, E. coli and enterococci could be detected in stool samples (57% and 67%, respectively). In contrast, with only one exception, ingested lactobacilli and bifidobacteria could not be detected in human feces.

Are probiotics detectable in human feces after oral uptake by healthy volunteers? 2007

In Species Probiotics MAY take up residency

This has been demonstrated with a few probiotics that are human sourced: Mutaflor and SymbioFlor-2. It does not occur 100%. My memory (speculation) is that the samples were these studies were the same general ethnic base (Germany) as the source of these strains (in one case, we know it was a German Soldier fighting in the Great War – i.e. E.Coli Nissle 1917). For myself (and my wife), we both have significant German DNA — and they both work for us.

At this point, we hit the end of our current understanding. To summarize the basics:

• 99% of commercial probiotics are pass thru. None detected after 24 hours.
  • Source is often animal
  • Makes the best business model for probiotic manufacturers — repeat business.
• For probiotics that are human sourced (i.e. from human stools!), the odds are better — often over 60% of people will have some after 24 hours.
• To know the source, you need to know the specific strain.
  • A species is “Lactobacillus Reuteri”
  • A strain is “Lactobacillus Reuteri RD830”
  • A few firms will also signify the human population group it was obtained from: “Lactobacillus Reuteri RD830-FR” , i.e. France

If you do not see the strain, do not buy you are tossing away your money. If you see the strain, you need to research if the source was human.

Probiotic Resistance

Probiotics displaces bad bacteria often in two ways:

• Outcompete other bacteria for food
• Produce natural antibiotics (bacteriocin) to kill bad bacteria. For example, Lactobacillus produce Reuterin, wikipedia states “Reuterin inhibits the growth of some harmful Gram-negative and Gram-positive bacteria, along with yeasts, molds, and protozoa “

As with antibiotics, continued use of the same probiotics will result in resistant harmful bacteria increasing to replace those that were not resistant. It is usually good to rotate every 2-4 weeks between different strains.