Probiotics: their action against pathogens can be turned around.

Area of Science:

• Microbiology
• Animal Science
• Aquatic Biology

Background:

• Probiotics can influence host health and pathogen interactions in complex ecosystems.
• Their efficacy is often context-dependent, influenced by environmental factors and host-microbe dynamics.

Purpose of the Study:

• To investigate the counter-intuitive effects of probiotic treatment on zebrafish (Danio rerio) challenged with a pathogenic Vibrio isolate.
• To explore the underlying mechanisms, including microbiome alterations and pathogen virulence modulation.

Main Methods:

• Zebrafish were treated with probiotics and subsequently challenged with a pathogenic Vibrio isolate at varying levels.
• Survival rates and histological analyses were conducted.
• Zebrafish microbiome composition, probiotic-pathogen genetic overlaps, and potential metabolomic and virulence changes were profiled.

Main Results:

• Probiotic-treated zebrafish exhibited higher survival rates at high pathogen challenge levels but lower survival at low challenge levels.
• Significant differences in fish survival and histology were observed.
• While the commensal microbiome architecture remained largely unchanged, probiotic-pathogen communication pathways may have been altered.

Conclusions:

• Probiotic administration can lead to unexpected, context-dependent outcomes, potentially by modulating pathogen virulence and host-microbe interactions.
• Further research is crucial to understand these complex interactions for optimizing probiotic applications in animal and human health.
• Findings can inform guidelines from organizations like FAO, OIE, and WHO.