Comparison of Selective Media for the Enumeration of Probiotic Enterococci from Animal Feed

Agnes Weiss, Konrad Johann Domig* and Wolfgang Kneifel

Division of Food Microbiology and Hygiene, Department of Food Science and Technology, BOKU – University of Natural Resources and Applied Life Sciences, Vienna Gregor Mendel Strasse 33, A-1180 Vienna, Austria

Article history:
Received September 7, 2004
Accepted February 28, 2005

Key words:
enterococci, media, enumeration, bile esculin azide agar, probiotic feed

Summary:
The project »Methods for the Official Control of Probiotics Used as Feed Additives« has been undertaken to develop and validate methods for the selective enumeration and strain identification of six probiotic microorganism genera (enterococci, lactobacilli, bifidobacteria, pediococci, bacilli and yeast). A diversity of media has been used for the detection, isolation and enumeration of enterococci. Aiming at the selective enumeration of enterococci (mainly Enterococcus faecium) present in probiotic animal feeds, either as a single component or in combination with other microorganisms, an extensive screening of published methods for culturing and enumerating enterococci was carried out. A collection of enterococcal strains used as probiotics in animal feeds and of isolates as well as reference strains from culture collections was established. Moreover, selected strains of lactobacilli, pediococci and streptococci were included for reference purposes. Based on a multitude of publications, twelve commercially available media were selected for testing and then compared with regard to their usefulness and selectivity. Bile esculin azide (BEA) agar showed good selectivity and pronounced growth of most enterococcal strains. Good reproducibility and electivity (esculin hydrolysis) as well as no influence of the feed matrix on the colony counts and a simple preparation procedure formed the basis for the proposed enumeration protocol. This work formed the basis for the enumeration protocol that was adapted to ISO format and validated in a collaborative study involving twenty laboratories from twelve European countries.

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