originated by Leifson,Selenite Broth is recommended as an enrichment medium for the isolation of Salmonella species from clinical and non clinical specimens such as faeces, urine or other pathological materials
Principle of Selenite Fluid Broth
- The peptone present in Selenite broth provides nitrogenous substances
- Lactose maintains the pH of medium
- Selenite is reduced by bacterial growth producing alkalinity which causes increase in pH which can reduce the toxicity of the selenite and results in overgrowth of other bacteria.
- The acid produced by bacteria by lactose fermentation counters the high pH and neutralizes the medium
- The addition of sodium phosphate is to maintains a stable pH and also minimizes the toxicity of selenite.
Enriched broth is subcultured on differential plating media such as Bismuth Sulphite Agar , Brilliant Green Agar,XLD Agar etc.
It should be noted that Selenite broth should not be incubated for longer than 24 hours as inhibitory effect of selenite decreases after 6 – 12 hours of incubation
Composition of Selenite Broth
|Peptone (Part A)||5.000|
|Lactose (Part A)||4.000|
|Disodium hydrogen phosphate (Part A)||10.000|
|(Part B)Sodium hydrogen selenite||4.000|
How to Prepare Selenite Fluid Broth
The preparation of Selenite Broth depends on each laboratory workload or the numbers of culture plates available. Anyway, note that a standard Petri dish is equivalent to 20ml when poured completely.
- Suspend 4.0 grams of (Part B) Sodium hydrogen selenite in 1000 ml purified/ distilled water.
- Add 19.0 grams of Part A.
- Mix well.
- Warm the mixture to dissolve the medium completely.
- Distribute in sterile test tubes.
- Sterilize in a boiling water bath or free flowing steam for 30 minutes.
DO NOT AUTOCLAVE.
Excessive heating is detrimental. Discard the prepared medium if large amount of selenite is reduced (indicated by red precipitate at the bottom of tube/bottle).
Caution : Take note that sodium hydrogen selenite (Sodium biselenite) is very toxic and corrosive agent and causes teratogenicity. Handle with great care.
If in case any contact with skin, wash immediately with lot of water
Appearance of Selenite F Broth
It has a cream to yellow clear to slightly opalescent solution
Type of Inoculums
- Water etc
Cultural characteristics after Incubation at 35-37°C for 18-24 hours.
|Salmonella Choleraesuis ATCC 12011||colourless|
|Salmonella Typhi ATCC 6539||colourless|
|Salmonella Typhimurium ATCC 14028||colourless|
|Escherichia coli ATCC 8739||pink with bile precipitate|
|Escherichia coli NCTC 9002||pink with bile precipitate|
How to store or conserve selenite Fluid broth
- Storage should be done below 30°C in tightly closed container at temperature 2-8°C.
- Klett A., 1900, Zeitsch Für Hyg. Und. Infekt., 33: 137.
- Murray PR, Baren EJ, Jorgensen JH, Pfaller MA, Yolken RH (editors) 2003, Manual of clinical Microbiology, 8th ed., ASM, Washington, D.C.
- Guth F., 1926, Zbl. Bakt. I. Orig., 77:487.
- Chattopadhyay W. and Pilford J. N., 1976, Med.Lab. Sci., 33:191.
- The Indian Pharmacopoeia 2007, Govt. of India, The Controller of Publication, Delhi