This document specifies a Pulsed Field Gel Electrophoresis (PFGE) methodology for the identification of authorized probiotic strains of Lactobacillus, Pediococcus, Enterococcus and Bacillus strains. The method can be applied to purified colonies obtained from cultured premixtures and feeds. The method can be used, even in the presence of a significant microbiological background, to verify the presence of microorganisms (strains and declared concentrations) used as feed additives in animal feeding stuffs.