Indole production is a positive test for which organism?

Indole production is a positive test for which organism?

• A. Escherichia coli
• B. Proteus mirabilis
• C. Salmonella Choleraesuis
• D. Serratia marcescens

Answer: (A)

Indole production shows whether an organism can convert tryptophan into indole using the enzyme tryptophanase. In the indole test, growth in a tryptophan-containing medium is followed by reagent addition; a positive result is indicated by a red color at the surface, showing indole is present. Escherichia coli commonly has tryptophanase and routinely produces indole, so it yields a positive indole test. The other organisms listed typically do not produce indole under standard testing conditions, giving negative results. Therefore, the indole-positive organism among them is Escherichia coli.

Indole production shows whether an organism can convert tryptophan into indole using the enzyme tryptophanase. In the indole test, growth in a tryptophan-containing medium is followed by reagent addition; a positive result is indicated by a red color at the surface, showing indole is present.

Escherichia coli commonly has tryptophanase and routinely produces indole, so it yields a positive indole test. The other organisms listed typically do not produce indole under standard testing conditions, giving negative results. Therefore, the indole-positive organism among them is Escherichia coli.