Selenite Enrichment Broth acc. to LEIFSON

Selenite Enrichment Broth

EMD Cat. No. 1.07717.0500

Medium proposed by LEIFSON (1936) for the selective enrichment of Salmonella from faeces, urine, water, foodstuffs etc.

The medium complies with the recommendations of the APHA (1992) for food examination.

Mode of Action	Preparation
Experimental Procedure and Evaluation	Quality Control
Typical Composition (g/liter)	Literature

Mode of Action
Selenite inhibits the growth of enteric coliform bacteria and enterococci, mainly during the first 6-12 hours of incubation. Salmonella, Proteus and Pseudomonas are not suppressed.

Preparation
Storage of the dehydrated culture medium below 15 °C!
Suspend 23 g/liter at room temperature; if the medium does not dissolve readily, heat briefly (max. 60 °C); if the medium is to be stored for a longer period of time filter-sterilize, dispense into suitable containers.
Do not autoclave.
pH: 7.0 ± 0.2 at 25 °C.
The prepared broth is clear and yellowish.
After a longer storage period of the dehydrated medium, the color of the prepared broth might change to reddish/red. The microbiological performance however is not affected.

Experimental Procedure and Evaluation
Add solid sample material to the normal-strength broth. Mix liquid samples with double-strength broth in the ratio 1:1.
Incubation: up to 24 hours at 37 °C - according to BÄNFFER (1971) and other authors, 43 °C is better.

After 6-12 hours and, if necessary, after 18-24 hours inoculate material from the resulting culture onto selective culture media.

Quality control

Test strains	Inoculum	Growth after
		24 hours
Escherichia coli ATCC 25922	approx. 99 %	10 %
Salmonella typhimurium ATCC 14028	approx. 1 %	90 %

Typical Composition (g/liter)
Peptone from meat 5.0; lactose 4.0; sodium selenite 4.0; di-potassium hydrogen phosphate 3,5; potassium dihydrogen phosphate 6.5.

Literature

BÄNFFER, J.R.: Comparison of the isolation of Salmonellae from human faeces by enrichment at 37 °C and 43 °C. - Zbl. Bakt. I. Orig., 217; 35-40 (1971).
LEIFSON, E.: New selenite enrichment media for the isolation of typhoid and parathyphoid (Salmonella) bacilli. - Am. J. Hyg., 24; 423-432 (1936).
American Public Health Association: Compendium of methods for the microbiological examination of foods. 3 rd ed., 1992