Final answer:
The TSI test results indicating the fermentation of lactose/sucrose reveals bacterial metabolic activities, with the aerobic respiration turning the slant red to purple and anaerobic fermentation showing acidic conditions by a color change to yellow in the butt.
Step-by-step explanation:
The TSI (Triple Sugar Iron) slant medium is used to differentiate bacteria based on their ability to ferment sugars and produce specific end products. In the case of lactose and sucrose fermentation, if the bacteria ferment both sugars, both the butt and the slant will appear red. The slant may become a deeper red-purple due to the production of increased amounts of acid during fermentation.
The question is related to the interpretation of the results of a Triple Sugar Iron (TSI) test which indicates whether bacteria can ferment sugars such as lactose or sucrose. The TSI slant is a medium that presents two environments for bacterial growth: one aerobic on the slant and one anaerobic in the butt. The media includes three sugars and a pH indicator that changes color according to the pH level influenced by bacterial metabolism. When lactose or sucrose is fermented by bacteria, acids are produced as a byproduct, leading to a change in color of the medium.
Specifically, the TSI test will show a red butt and red slant, with the slant potentially turning a deeper red-purple as a result of aerobic respiration, where the bacteria use oxygen and produce more alkaline byproducts, raising the pH. If a bacteria can ferment glucose under anaerobic conditions, this will be indicated by an acid reaction (color change to yellow) in the butt. On the other hand, the presence of facultative anaerobes can be inferred from the fact that growth occurs both on the slant and in the butt. Additionally, if H₂S is produced, indicative of either anaerobic respiration using sulfur or sulfate or from the breakdown of sulfur-containing amino acids, there will be a blackening of the media.