Esculin hydrolysis by Gram positive bacteria. A rapid test and it's comparison with other methods

A number of bacteria hydrolyze esculin enzymatically to esculetin. This characteristic is used by taxonomists and clinical microbiologists in the differentiation and identification of bacteria, especially to distinguish Lance-field group D streptococci from non-group D organisms and Listeria monocytogenes from morphologically similar Erysipelothrix rhusipoathiae and diphtheroids. Conventional methods used for esculin hydrolysis require 4--48 h for completion. We developed and evaluated a medium which gives positive results more rapidly. The 2,330 isolates used in this study consisted of 1,680 esculin positive and 650 esculin negative organisms. The sensitivity and specificity of this method were compared with the PathoTec esculin hydrolysis strip and the procedure of Vaughn and Levine (VL). Of the 1,680 esculin positive organisms, 97% gave positive reactions within 30 minutes with the rapid test whereas PathoTec required 3--4 h incubation for the same number of organisms to yield a positive reaction.