The probiotic paradox: live and dead cells are biological response modifiers

Area of Science:

• Microbiology
• Immunology
• Gastroenterology

Background:

• Probiotics are defined as live non-pathogenic microorganisms conferring health benefits.
• Probiotics exhibit various gastrointestinal effects, including anti-inflammatory and immunomodulatory actions.
• Many beneficial effects attributed to probiotics are also observed with dead microbial cells.

Purpose of the Study:

• To investigate the "probiotic paradox," where both live and dead probiotic cells elicit biological responses.
• To explore the dual action of probiotics, involving live cells influencing microflora and immune response, and dead cells mediating anti-inflammatory effects.
• To highlight the implications of dead probiotic cell activity for product development and application.

Main Methods:

• Review of existing literature on probiotic mechanisms of action.
• Analysis of studies using heat-killed probiotics (e.g., Enterococcus faecalis, Bifidobacteria) in various animal models (chicks, dogs).
• Examination of immune responses, including cytokine production (TNF-alpha) and phagocyte activity, following administration of dead probiotics.

Main Results:

• Heat-killed Enterococcus faecalis stimulates the gastrointestinal immune system in chicks.
• Dead bifidobacteria significantly increase TNF-alpha production.
• Administration of heat-killed E. faecalis to dogs enhances neutrophil phagocytosis.

Conclusions:

• The "probiotic paradox" suggests that both live and dead probiotic cells contribute to beneficial biological responses.
• Probiotic action may be dual: live cells modulate microflora and immunity, while dead cell components provide anti-inflammatory effects.
• Dead probiotics offer advantages like enhanced safety and longer shelf-life, functioning as biological response modifiers.