In this study, MRS medium supplemented with cysteine hydrochloride and mupirocin, termed Bifidobacterium selective medium (BSM) was found to be elective for bifidobacteria but inhibitory to a wide range of non-bifidobacteria strains commonly included in probiotic animal feed. Bacilli, lactobacilli, lactococci and streptococci failed to form colonies on BSM and enterococci, pediococci and propionibacteria formed colonies < 0.5 mm in diameter. Bifidobacteria formed colonies > 1 mm in size and could be readily distinguished. The addition of nystatin to BSM further inhibited Saccharomyces cerevisiae. BSM was successfully used to enumerate the bifidobacteria components, confirmed through fructose-6-phophate-phosphoketolase detection, present in two commercial probiotic feeds. The medium is recommended for the enumeration of bifidobacteria from animal feeds especially when not a numerically dominant component. (C) 2003 Elsevier B.V. All rights reserved.