Selenite Fluid Broth Principles,composition and colony characteristics

culture-media-prac-microbiology-24-638

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

IngredientsGrams/Litres
Peptone (Part A)5.000
Lactose (Part A)4.000
Disodium hydrogen phosphate (Part A)10.000
(Part B)Sodium hydrogen selenite4.000

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.
Also read  Laboratory Diagnostic of Hymenolepis nana (Dwarf tapeworm)

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

  • Urine
  • Stool
  • blood
  • Water etc

Cultural characteristics after Incubation at 35-37°C for 18-24 hours.

OrganismsColony color
Salmonella Choleraesuis ATCC 12011colourless
Salmonella Typhi ATCC 6539colourless
Salmonella Typhimurium ATCC 14028colourless
Escherichia coli ATCC 8739pink with bile precipitate
Escherichia coli NCTC 9002pink 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.

Reference

  • 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

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About the Author: Arthur Westmann

DEFFE ARTHUR (AMOEBAMANN) is the founder and author of MLTGEEKS and MLTEXPO.He’s from Cameroon and is currently a Final year State Medical Laboratory Technician (MLT MA). Beyond lab works, he’s a passionate internet user with a keen interest in web design and blogging. Furthermore He likes traveling, hanging around with friends and social networking to do in his spare time.

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2 Comments

  1. This is very good. It keeps me updated on medical laboratory practice so as to be more vibrant competent and skillful.
    Thanks MLTGEEKS

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