Question

Upon performing a phenol/ sugar fermentation test, you analyze your test tubes for production of acid and gas. for each type of bacteria describe what you would see ( i.e what color the tube would be, whether gas is present or not) a) obligate anaerobe that ferments glucose to acetic acid and CO2 b) aerotolerant anaerobe that ferments glucose to acetic acid and CO2 c) a facultative anaerobe that can respire and can ferment glucose to alcohol and c02 d) an obligate aerobe that respires only the indicator is bromthymol blue

Answer 1

Sugar fermentaion test is dependent on type of microbe species and anaerobe or aerobic conditions. If acid is produced due to fermentation of sugar , it would lower the pH and the indicator , here bromothymol blue would change from green to yellow and gas production will be seen as bubble production in durhams tube.

A- since both acid and gas - Yellow color and bubble would be seen.

B- In this also yellow color and bubble seen.

C- Since here acid is not produced , only bubble will be seen in durhams tube.

D- Since this does not ferment no change of color or bubble will be seen.