Council Directive 70/524/EEC regulates the application of probiotic (microorganisms) additives in feeding stuffs. In the present study a method for the differentiation and strain identification of authorised probiotic Saccharomyces cereviseae strains in feeding stuffs by Polymerase Chain Reaction (PCR) was validated. Four different samples of animal feeding stuffs containing yeast at levels between 105 to 107 CFU/g were examined. Samples were enumerated on chloramphenicol glucose yeast extract agar and
colonies were selected from these plates for DNA extraction and subsequent analysis. The PCR method
using delta sequence primers produced an ‘amplified sequence polymorphism’ characteristic for the test
strain. Feeds supplemented with one of four probiotic yeast strains each were analysed by seven of nine
invited laboratories. All laboratories returned valid results with the exception of one laboratory that had
insufficiently separated bands on the gel. The method had a good reproducibility for probiotic yeast isolates
from feed of all four authorised probiotic yeast strains (APYS) CBS 493.94, APYS CNCM 1-1079,
APYS CNCM 1-1077, APYS NCYC SC47 and of a commercially available yeast reference strain, NCYC
81. The PCR method is to be considered by CEN and ISO as official control method for identification of
authorised probiotic Saccharomyces cerevisiae strains from feeding stuffs.