Assessing Bacterial Viability and Label Accuracy in Human and Poultry Probiotics Sold in the United Kingdom

Accurate label claims are essential for consumer trust in probiotic efficacy, yet limited datasets are available for poultry formulations marketed in the United Kingdom. We quantified and identified the viable bacteria in twelve commercial probiotics, seven for poultry and five for human use, using selective plate counts and MALDI-TOF MS. Observed colony forming units (CFU) were compared with declared values using one-sample t-tests, adopting a practical acceptance range of ±0.5 log CFU. Poultry products largely met or exceeded their labels (e.g., P5: 1.4 × 1010 CFU g−1 vs. 2 × 109 CFU g−1 declared), whereas human products delivered greater variability in both species composition and stated CFU count; one contained no detectable viable bacteria. All products deviated significantly from their label claims (p < 0.05); however, 11 of 12 met the ±0.5 log10 CFU benchmark—10 within the range and 1 above its “≥” value—leaving only one probiotic below the threshold. MALDI-TOF MS confirmed the presence of most labelled species, though Bifidobacterium bifidum was absent from one human product and Bacillus isolates were re-assigned to B. velezensis/B. amyloliquefaciens. These findings indicate robust quality assurance in UK poultry probiotics, but substantial under-delivery in the human probiotics, underscoring the need for harmonized viability standards and tighter post-market surveillance.