Selenite Broth was invented by Leifson who proved that selenite is inhibitory to bacteria, coliforms, and other species, like streptococci from feces, which are found in fecal samples and, consequently, beneficial in the recuperation from Salmonella species. Selenite-F Broth is utilized to enrich the environment that is buffered by Lactose Peptone Broth to which Sodium Biselenite is added to act as the agent that is selective for elimination of Salmonella from urine, feces and water, as well as food items and other substances that are of sanitary significance.
Principle of Selenite F Broth
Casein enzyme hydrolysate is a carbon compounds, nitrogenous substances as well as vitamin sources. Lactose is a source of carbohydrate that helps maintain your medium’s pH. Selenite is decreased through bacterial growth, and alkali is created. The increase in pH decreases the toxicity of selenite. This leads to an growth of the other bacteria. The acid created by bacteria as a result of lactose fermentation is used to ensure the pH to a neutral. The sodium phosphate helps maintain the pH of the water and reduces the toxicity of selenite. Sodium hydrogen selenite (Sodium biselenite) is a poisonous, corrosive, and toxic substance that is a teratogenic agent. It inhibits several kinds of gram-positive and negative bacteria, including enterococci and coliforms. It is not recommended to allow the broth to remain incubated for more than 24 hours since the inhibitory effects of selenite diminishes after 6 to 12-hours of treatment.
Composition of Selenite F Broth
|Casein enzymic hydrolysate||5.0|
|Sodium hydrogen selenite||4.0|
pH at 25°C 7.1 ± 0.2
Preparation of Selenite F Broth
- Add 4.0 grams sodium selenite powder to the deionized/distilled water.
- Add the remaining 19.0 grams of powder to the above solution and increase the volume to 1.0 Liter.
- Then gently heat it and reduce to a boil.
- Dispense into sterilized test tubes, at a minimum with a diameter five centimeters.
- Sterilize in a boiling water bath or with free flow of steam for 10 minutes.
- DO NOT AUTOCLAVE.
- Recool to room temperature prior to using.
Result Interpretation on Selenite F Broth
- After incubation , the growth of organisms is evident by the presence of an increase in the level of turbidity within the medium.
- Subculture characteristics of culture when it comes to MacConkey Agar following incubation of the agar at 35-37 degrees Celsius for 18-24 hours are described as follows:
- Positive Result: Colorless, Good Growth.
- Examples:Salmonella Typhimurium, Shigella sonnei, Salmonella enteritidis, etc.
- Negative Result: Pink with bile precipitate, inhibited Growth or No growth.
- Examples: Escherichia coli, Enterococcus faecalis, etc.
Uses of Selenite F Broth
- Selenite F Broth can be used as a selective enrichment solution for growing Salmonella Spp.
- It can also be employed as an enrichment method to isolate some types of Shigella.
- It is also suggested to transport Vibrio cholerae strains, since these bacteria can live for up to 5 day for up to 5 days in Sodium Selenite Broth.
Limitations of Selenite F Broth
- Sodium hydrogen selenite (Sodium biselenite) is a highly harmful, corrosive and toxic agent that is a teratogenic agent. Take care when handling it. If contact occurs with the skin, rinse it immediately with lots of water.
- Enrichment broths shouldn’t be used solely as an isolation medium. They should be utilized together with plates that are non-selective and selective to increase the likelihood of isolating pathogens when they are present in small quantities.
- Due to the variation in nutrition Certain strains could be encountered that are unable to grow or do not grow well in this medium.