Question

One of the following bacteria is in a sample: Staphylococcus aureus, Citrobacter freundii, Bacillus subtilis, Proteus vulgaris and Enterococcus faecium. After Gram staining and visualization of the sample by brightfield microscopy, the identification of the bacterium was narrowed to two possibilities. An indole test was performed on the bacterium and produced a negative indole test result. This was enough information to determine the identity of the microorganism. Which microorganism was in the sample? (2 pts)

Answer 1

indole test is performed to check the abilities of the bacterias of changing tryptophan into indole.

from the name of the bacterias mentioned above, enterococcus faciem gives positive indole test - apperance of a red or red-violet color in the surface alcohol layer of the broth.

Bacillus subtilis gives negative indole test : presence of yellow color.

therefore Bacillus subtilis is present in the sample