Carbohydrate Fermentation (BCP Test)

What is the purpose of Bromcresol Purple (BCP) in the carbohydrate fermentation test?

It is a pH indicator. Yellow = acid production (fermentation); Purple = no acid (alkaline).

What does a yellow broth in the BCP test mean?

Acid is produced from carbohydrate fermentation.

What does a purple broth in the BCP test mean?

No acid produced (no fermentation).

What is the purpose of the Durham tube?

To detect gas production (bubble = gas).

What does “acid/gas” (+/+) mean in BCP fermentation results?

Acid was produced (yellow broth) and gas was produced (bubble in Durham tube).

What does “acid/no gas” (+/-) mean?

Fermentation occurred with acid production but no gas released.

What does “no acid/no gas” (-/-) mean?

No fermentation occurred.

What is reversion in carbohydrate fermentation?

When bacteria initially ferment and turn the medium yellow, but then use peptones and release alkaline products, turning the medium back to purple.

At the 24-hour check, your broth is purple. What is the next step?

Continue incubating (up to 7 days) to confirm whether the organism can ferment the sugar.

E. coli fermentation results in glucose broth?

Yellow broth with bubble \rightarrow acid and gas production (+/+).

E. coli fermentation results in sucrose broth?

Purple, no bubble \rightarrow no acid, no gas (-/-).

Staphylococcus xylosus fermentation results in glucose broth?

Brownish/yellow with bubble \rightarrow acid and gas (+/+).

Staphylococcus xylosus fermentation results in sucrose broth?

Brownish/yellow, no bubble \rightarrow acid only (+/-).