Applicability of a colorimetric method for evaluation of lactic acid bacteria with probiotic properties

- Resazurin cannot be used to measure lactic acid bacterial growth because of low pH.
- The WST-8 assay is a rapid, accurate, and sensitive approach for screening LAB.
- The WST-8 assay is useful for screening for LAB resistant to acid and bile.

Rapid colorimetric methods using various indicator reagents have been developed to monitor bacterial viability. Here, we examined the applicability of a method based on the reduction of resazurin or water-soluble tetrazolium salt-8 (WST-8) to screen lactic acid bacteria (LAB) for growth, tolerance against bile acid and low pH. The resazurin reduction test proved unsuitable for screening LAB such as Lactobacillus plantarum and Leuconostoc mesenteroides since it reacted with acid present in the cultures. LAB growth could be indirectly quantified by measuring WST-8 reduction. This method proved more sensitive and quickly results than counting bacterial colony forming units and turbidity at 600 nm in the presence of bile and acid. Our results suggested that the WST-8-based method could be useful for the characterization of growth and tolerance of the lactic acid producing bacteria.