Which biochemical test is used to confirm the presence of Enterococcus?

The bile esculin test is specifically designed to identify Enterococcus species through their ability to hydrolyze esculin in the presence of bile salts. Enterococcus has a unique characteristic of growing in bile and converting esculin to esculetin, which then reacts with iron salts in the medium to produce a dark brown or black precipitate, confirming its presence.

In contrast, other tests listed serve different purposes. The Quellung test is primarily utilized for identifying encapsulated bacteria, particularly those from the Streptococcus pneumoniae, based on capsule swelling. The optochin test is used to differentiate Streptococcus pneumoniae from other alpha-hemolytic streptococci, with sensitivity to optochin being a key factor. The CAMP test assesses the synergistic hemolysis of certain bacteria, especially in Streptococcus agalactiae, showing its ability to enhance hemolytic activity when combined with Staphylococcus aureus.

While all these tests are valuable in their respective contexts, the bile esculin test is the definitive choice for confirming Enterococcus.