Bile Esculin Azide Broth is a selective medium for the differentiation, isolation and presumptive identification of enterococci. The ability to hydrolyze esculin is a characteristic of enterococci. Organisms positive for esculin hydrolysis, hydrolyze the glucoside esculin to esculetin and dextrose. The esculetin reacts with the ferric citrate to form a dark brown or black colony. Ox bile does not inhibit enterococci while other Gram positive bacteria are inhibited. Sodium azide inhibits Gram negative bacteria. Tryptone, peptone and yeast extract supply the nutrients essential for growth. Sodium chloride provides the osmotic balance. Bacteriological agar is the solidifying agent. The presence of intestinal enterococci, is an indicator for faecal contamination, especially when the contamination occurred a long time before and the less resistant coliform bacteria, including Escherichia coli, may already be dead when the analysis is carried out.
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