Question

Following an 18-24 hour incubation period, what can you conclude from a TSI agar if the top is red and the butt is yellow? The inoculated bacterium can only ferment glucose The inoculated bacterium can only ferment sucrose The inoculated bacterium can only ferment lactose The inoculated bacterium is able to ferment all the sugars in the agar The inoculated bacterium cannot ferment

Answer 1

TSI slant test is the test for distinguishing bacteria depending on the fermentation type of sugars .

TSI SLANT contains phenol red which can chnages into yellow when the pH of the solution reduces because of deposition of acids like lactic acids .

Here, after 18 hours, lactose present in upper slant can be converted into other products by aerobic conditions.

But when, these fermentation start , lactose is produced and the pH reduced and the phenol red become yellow but after 18 hours oxygen supplies become sufficient and the lactose become converted into pyruvate or other products or lactose is not produced, that why the upper slant become red as the original colour of phenol red..

So, this TSI CONTAIN ONLY GLUCOSE FERMENTER .

IF THE BACTERIA WOULD LACTOSE FERMENTAR THEN, BOTTOM LATER ALSO BECOME YELLOW BECAUSE LACTOSE IS PRODUCED and it converts red colour into yellow.

So, the answer is only glucose fermenter present.

Thank you