Why do commercial probiotics often fail to colonize the human gut?
Contrary to what you may hear, it's not a matter of concentration.
1️⃣ Non-native strains: Many probiotic strains are not native to the human gut and therefore haven't evolved the specific genetic traits that allow them to survive and thrive in the gut environment. These traits include:
🎯 Mucosal adherence: The ability to stick to the gut epithelial lining.
🎯 Acid resistance: Surviving the harsh, acidic environment of the stomach.
Without these adaptations, non-native probiotic strains struggle to establish themselves and colonize effectively.
2️⃣ Niche availability and competition: The gut microbiome is a complex ecosystem with limited space and resources. For a probiotic strain to colonize, it needs to find an available niche. This can be challenging because:
🎯 Existing bacteria may already occupy suitable niches.
🎯 Microbes face intense competition for resources.
One study found that a specific strain of Bifidobacterium longum had more success colonizing in individuals who didn't already have native B. longum strains. This suggests that when a niche is already filled by a similar species, it's harder for the probiotic strain to establish itself.
3️⃣ The "like will to like" principle: This principle states that probiotic strains have a better chance of colonizing when there are already related species present in the gut microbiome. This might seem contradictory to the previous point, but it suggests that:
🎯 A similar microbial environment may be more hospitable to the incoming probiotic strain.
🎯 The presence of related species might indicate that the gut environment is suitable for a particular type of microbe.
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