Question

You inoculate 2 SIM tubes with 2 different microbes. You check your results after 48 hours, adding Kovacs reagent. You discover microbe 1 has turned the agar entirely black and the Kovacs reagent is red. Microbe 2 has not changed the color of the agar, the growth is confined to the stab line, and the Kovacs is yellow.

A) Interpret these results.

B) What can you conclude about the microbes (metabolically and structurally) based upon these results, and why?

Answer 1

A- Kovacs reagent is the mixture of Isoamylalcohol, para-dimethylaminobenzaldehyde (DMAB), and concentrated hydrochloric acid. Microorgamsini which uses Tryptophan releases Indole. This indole reacts with, para-dimethylaminobenzaldehyde and gives red color.

A- Microbes in tube 1 are indole positive and microbes in tube 2 are indole negative.

B- The microbe in tube 1 can produce the enzyme tryptophan which degrades tryptophan into indole, pyruvate, and ammonia are released as the source of energy. Indole test is a part of  IMViC series test which is generally performed for enteric bacteria. So microbe 1 might be enteric bacteria