Which of the following organisms is commonly tested for with an indole test?

The indole test is primarily used to determine the ability of an organism to convert tryptophan into indole, which is an important characteristic for identifying certain bacteria. Escherichia coli is well-known for producing indole when it metabolizes tryptophan. Thus, a positive reaction in the indole test (indicating red color when adding Kovac's reagent) confirms the presence of E. coli, making it a key organism commonly tested using this method.

Other organisms listed do not typically yield a positive indole test, making E. coli the standout choice for this assay. Burkholderia cepacia, Salmonella enterica, and Streptococcus pyogenes either do not produce indole or are not characterized primarily using this test, emphasizing the specificity of the indole test for identifying E. coli in laboratory settings.