[Bile].

Abstract

Our Bile Esculin Agar (BEA) is used as a differential medium for the isolation and presumptive identification of group D streptococci and enterococci from clinical specimens and food. This medium is also useful for differentiating Klebsiella, Enterobacter, and Serratia species from other Enterobacteriaceae. Swan was the first to describe the formulation and use of a bile esculin medium, although Rochaix (1924) was the first to note the value of using esculin hydrolysis to identify enterococci. During their comparative studies, Facklam and Moody demonstrated that Bile Esculin Agar was a reliable method of presumptively identifying group D streptococci and differentiating them from other streptococci. Lindell and Quinn as well as Edberg’s group showed that Bile Esculin Agar could also be used for the rapid differentiation of Enterobacteriaceae based on esculin hydrolysis later showed it. Gelatin peptone and beef extract provide the essential elements needed for growth. The inclusion of esculin allows for detection of esculi nhydrolysis by the bacterial enzyme, esculinase. Esculin hydrolysis liberates esculetin, which in turn reacts with ferric ions (ferric citrate) in th e medium to produce a black iron-complex giving esculinase-positive colonies a brown-black halo. Selectivity is accomplished by the addition of bile (oxgall), which inhibits the growth of most grampositive cocci other than enterococci and group D streptococci.