Question

44. Which media/tests can be used to exhibit gas production?

1. Citrate
2. PRG
3. TSI
4. A and B
5. B and C

Answer 1

44. Answer - B and C

PRG and TSI media/tests can be used to exhibit gas production.

Reason - TSI (Triple Sugar Iron) media contains three sugars- lactose, sucrose, dextrose and ferrous sulfate, peptone as well as a pH indicator phenol red. If the bacteria uses any of the three sugars, then the media will turn yellow. The colour change is due to carbohydrate fermentation that leads to acidification of the medium and phenol red acts as an pH indicator. If the bacteria reduces sulfur, then H2S (hydrogen sulfide) gas will be produced that can be seen as a black precipitation. Because the H2S reacts with iron and iron sulfide is formed. Moreover, the CO2 and H2S gas production by the organism can be concluded through the cracks or bubbles in the medium or through the raising of the slant or media from the bottom surface.

PRG (Phenol Red Glucose) media contains glucose and phenol red. The fermetaion of glucose change the colour of the medium from red to blue. If there is gas production, buubles will appear upon inverting Durham tube. A smaller test tube is inserted upside down in another test tube. The bubbles are trapped inside the smaller tube.

Citrate media contains sodium citrate and bromothymol blue as a pH indicator. This test is used to examine the ability of a bacteria to utilize citatre. The citrate-negative bacteria can also grow on this media as inorganic salts are also present as nitrogen source. If bacteria utilizes citrate, then growth along with colour change will appear. The green colour media turns to blue.