ISO 19344:2015 specifies a standardized method for the quantification of active and/or total lactic acid bacteria and probiotic strains in starter cultures used in dairy products by means of flow cytometry. The method is also applicable to probiotics used in dairy products and to fermented milk products such as yogurts containing primarily lactic acid bacteria.

This International Standard does not apply to taxonomical differentiation of bacteria. Due to its non-specificity, the method may quantify other bacteria than those within the scope of this International Standard, when present in the sample. This may lead to overestimation of the counts.

The minimum bacterial cell concentration in the sample before applying this standardized method depends on the dilution rates used in the individual protocols. Typically 10⁶ cells per gram or ml are considered within the minimum range.