Insights into the enumeration of mixtures of probiotic bacteria by flow cytometry

To investigate the suitability of a general gating strategy for enumeration of multi-species probiotic blends with live/dead staining. Gating strategy was designed based on cytograms of individual freeze-dried probiotic preparations (CUL21/60, CUL20/34, CUL08, CUL66N and CUL61) before being applied to different combinations of these organisms. FC results were compared to plate counts.
Conclusion:
Live/dead flow cytometry can be used to enumerate single and mixed populations of probiotic bacteria more accurately/reliably than the gold standard plate count technique. However the accuracy of multi-species enumeration is impacted by the composition of the blend with the potential of FC to over-enumerate in some cases. However, the over-enumeration of FC is not as severe as the under-enumeration by plate counts. We conclude that any effort to gate multi-species products must first assess the gating strategy on the individual bacterial components to determine potential inaccuracies in the method.
Notes:
Only 1 replicate of each batch of individual freeze-dried preparation and multi-species blend is uploaded.