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Probiotic nutrition is frequently claimed to improve human health. In particular, live probiotic bacteria obtained with food are thought to reduce intestinal colonization by pathogens, and thus to reduce susceptibility to infection. However, the mechanisms that underlie these effects remain poorly understood. Here we report that the consumption of probiotic Bacillus bacteria comprehensively abolished colonization by the dangerous pathogen Staphylococcus aureus in a rural Thai population. We show that a widespread class of Bacillus lipopeptides, the fengycins, eliminates S. aureus by inhibiting S. aureus quorum sensing-a process through which bacteria respond to their population density by altering gene regulation. Our study presents a detailed molecular mechanism that underlines the importance of probiotic nutrition in reducing infectious disease. We also provide evidence that supports the biological significance of probiotic bacterial interference in humans, and show that such interference can be achieved by blocking a pathogen's signalling system. Furthermore, our findings suggest a probiotic-based method for S. aureus decolonization and new ways to fight S. aureus infections.
There is increasing appreciation of the key role that the intestinal microbiota play in preventing the colonization and overgrowth of pathogens1,2. The mechanisms that have been implicated in this beneficial function of probiotic bacteria are mostly indirect, and include modulation of the immune system, enhancement of the intestinal epithelial barrier, or competition with pathogens for nutrients2-5. Whether there is direct interference between probiotic and pathogenic bacteria is less clear. Some probiotic strains produce bacteriocin proteins, which can kill phylogenetically related pathogenic bacteria2, and it has been shown that a bacteriocin-producing Escherichia coli strain inhibits colonization by related pathogenic bacteria in the inflamed gut of mice6. However, no evidence has been obtained to indicate that such mechanisms matter or are widespread in humans. Furthermore, it is not known whether there are mechanisms for direct probiotic bacterial interference that are not mediated by bacteriocins.
The genus Bacillus comprises different species of soil bacteria that form endospores with the ability to survive harsh environmental conditions, such as the high temperatures encountered during cooking procedures. Bacillus spores are commonly ingested with vegetables7. They can subsequently germinate to form metabolically active, vegetative cells8, which can temporarily colonize the intestinal tract9. Given the variability in dietary customs, the concentration of Bacillus spores in human faeces...