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Probiotic Viability Reconsidered: Integrating VBNC Resuscitation and Culture-Independent Methods for Accurate
Sara Arroyo-Moreno1, Gonzalo Saiz-Gonzalo1, Seamus McSweeney1
1AnaBio Technologies, T45 RW24 Carrigtwohill, Co. Cork, Ireland.
Abstract:
Probiotic enumeration in foods and beverages remains anchored in culture dependent colony-forming unit (CFU) counts, the regulatory gold standard for label compliance. However, culturability does not fully equate to viability as environmental stresses can convert probiotic cells into a viable but non-culturable (VBNC) state, where they remain metabolically active but undetectable by CFU counts. Microencapsulation can provide a degree of protection to probiotics against stress; nevertheless, this blind spot in quantification forces manufacturers to overdose formulations or risk non-compliance with health benefits claims. Thus, the efficacy of probiotics may be underestimated when evaluation relies solely on CFU, creating a false dichotomy between VBNC and non-viable cells. Culture-independent methods, including flow cytometry quantification of active fluorescent units (AFUs), viability PCR/dPCR, and rRNA-targeted Flow-FISH, can aid closing this gap by detecting metabolically active cells non-detectable by culturing, providing complementary quantification data to CFU counts alone. Understanding the relationship between quantification by culture and culture-independent methods provides a more accurate measure of probiotic dose delivery in functional foods and beverages. This review covers the current understanding of VBNC state, including induction, detection, and resuscitation in probiotics, with emphasis on experimental controls that differentiate true VBNC resuscitation from population growth. Case studies in Lactobacillus and Bifidobacterium illustrate triggers, molecular mechanisms, and methodological advances. Finally, guidance is provided for the development of an integrated quantification approach that reconciles culture-dependent and culture-independent data, ultimately aiming to improve CFU count accuracy through the controlled resuscitation of VBNC cells.
Insights
Probiotic quantification using colony-forming unit (CFU) counts may underestimate viability due to the viable but non-culturable (VBNC) state. Culture-independent methods offer complementary data for accurate probiotic dose delivery in foods.
Area of Science:
- Microbiology
- Food Science
- Biotechnology
Background:
- Current probiotic enumeration relies on colony-forming unit (CFU) counts, the regulatory standard for label compliance.
- Environmental stresses can induce a viable but non-culturable (VBNC) state in probiotics, rendering them undetectable by CFU counts despite metabolic activity.
- This quantification gap can lead to product over-dosing or underestimation of probiotic efficacy in functional foods and beverages.
Purpose of the Study:
- To review the current understanding of the viable but non-culturable (VBNC) state in probiotics, including its induction, detection, and resuscitation.
- To highlight the limitations of culture-dependent methods (CFU) and the potential of culture-independent methods for accurate probiotic quantification.
- To provide guidance for an integrated approach reconciling culture-dependent and culture-independent data for improved probiotic dose accuracy.
Main Methods:
- Review of literature on VBNC state induction, detection (e.g., flow cytometry, viability PCR/dPCR, Flow-FISH), and resuscitation in probiotics.
- Analysis of case studies involving *Lactobacillus* and *Bifidobacterium* to illustrate triggers, molecular mechanisms, and methodological advancements.
- Emphasis on experimental controls to differentiate true VBNC resuscitation from population growth.
Main Results:
- Culture-independent methods can detect metabolically active cells in the VBNC state, which are missed by traditional CFU counts.
- Understanding VBNC dynamics is crucial for accurate assessment of probiotic viability and efficacy.
- Integrated quantification approaches combining CFU and culture-independent data can provide a more comprehensive measure of probiotic dose.
Conclusions:
- Accurate probiotic enumeration requires methods that account for the VBNC state, moving beyond solely CFU counts.
- Culture-independent techniques offer valuable complementary data for assessing probiotic viability and ensuring product efficacy.
- Developing integrated quantification strategies is essential for improving the accuracy of probiotic dose delivery in functional foods and beverages.
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