Positive Test Result: Tubes must be lemon yellow to be considered positive for lactose or sucrose fermentation. Positive tests are recorded with an “A” for acid. Negative test result: Orange or red are considered negative for fermenting sugar.
What does a positive fermentation test mean?
Positive: Development of a yellow color in the medium indicates a positive carbohydrate fermentation reaction. Negative: The absence of yellow color indicates a negative carbohydrate fermentation reaction. Gas formation is indicated by the appearance of gas bubbles in the Durham tray
What do sugar fermentation tests tell us?
The carbohydrate fermentation test is used to determine whether or not a bacterium can utilize a particular carbohydrate. It tests for the presence of acid and/or gas resulting from the fermentation of a single specific carbohydrate.
What does a positive sucrose fermentation test mean?
Yellow Positive: After incubation, the liquid in the tube turns yellow (indicated by the color change of the phenol red indicator). It indicates that the pH is dropping due to acid production from the fermentation of the carbohydrate (sugar) present in the medium.
What result would indicate a positive carbohydrate fermentation test?
A yellow color change in the fermentation medium indicates a positive (+) test. The basis for this change is that the fermentation of carbohydrates leads to the production of pyruvic acid, which causes the media to change color from purple to yellow due to the reduction in pH below 6.8.
What is the Glucose Fermentation Test used for?
It tests an organism’s ability to ferment the sugar glucose and its ability to convert the end product of glycolysis, pyruvic acid, into gaseous by-products. This is a test commonly used to identify enteric gram-negative bacteria, all of which are glucose fermenters but only some of them produce gas.
What is the principle of sugar fermentation test?
The principle of carbohydrate fermentation states that the action of an organism on a carbohydrate substrate leads to acidification of the medium, which is detected by a pH indicator dye.
What is the sucrose fermentation test used for?
The goal is to see if the microbe can ferment carbohydrate sucrose as a carbon source.