Detect Lactose Fermenters

In the laboratory, how to detect lactose fermenters depends on the method used. Several different types of fermentation media can be used to identify these bacteria. These mediums can be selective, nonselective, or both. Different species of bacteria are capable of fermenting a variety of carbohydrates.

fermenters agar is a selective bacterial culture medium. It can be used to identify lactose-fermenting and non-lactose-fermenting bacteria. This medium is commonly used to detect Enterobacteriaceae.

Lactose fermenters are organisms that break down lactose into glucose and galactose. When this occurs, the pH level of the medium will be acidic. Some bacteria can also ferment other monosaccharides. While most of these organisms will produce a red or pink colony, some will produce a white or opaque colony. A red or yellow butt can be seen if the colony is formed by a lactose-fermenting organism. During this phase of growth, there will also be a zone of precipitated bile salts surrounding the colony.

How to Detect Lactose Fermenters

The MUG test is another type of differential medium that can be used to differentiate lactose fermenters from nonfermenters. The test involves the addition of a disc containing 5% sheep blood cells. Once this is added, the suspension of the bacteria will change color. If the bacteria are lactose fermenters, the disc will add an indicator known as ONPG. As the pH of the medium changes, the ONPG indicator will become orange or pink. However, if the bacteria are nonfermenters, they will not add an indicator.

Durham tubes are small glass tubes with a slant that enables them to be placed inside a larger glass tube containing a fermentation medium. This helps to prevent air from entering the tube and thus reducing the amount of gas that is produced. When the bacteria start to ferment the carbohydrate in the medium, the gases will be trapped inside the tube. They will then lift the agar off the tube.

To perform this test, inoculate the tube with the sample. Place it in an incubator at 35-37 C for 24 hours. After the first few hours, the tube will appear a little yellow. If there is no change in color, the tube was probably not inoculated correctly. Alternatively, the test can be done after the inoculated sample has been removed from the incubator.

Other ways to detect lactose fermenters are through enzyme testing and by comparing the rate at which the lactose is broken down. Different species of lactose-fermenters will show varying rates of growth, and the pH of the medium will be changed in the process. For instance, Escherichia coli will produce an acid mixture when it is inoculated. Using an indicator such as methyl red, this can be detected. Similarly, the presence of a red slant is a positive sign that the sample has been inoculated.

Besides lactose, a variety of other carbohydrates can be used as a substrate for the fermentation process. Some organisms will use glucose, while others will convert other monosaccharides into glucose. Bacteria can also ferment aromatics, such as acetylene.