Description

Use and description:

The medium was developed to detect Salmonella spp, especially rapid lactose fermenting organisms like S. arizona by lysine decarboxylase activity and H2S production. S. arizona strains due to the quick lactose fermentation suppress the positive H2S reaction on TSI agar. To overcome this problem was this medium established.

 

Composition per litre:

Peptones………………………………………..…… 5.00 g

Yeast extract………………………………………….3.00 g

Glucose………………………………………………….1.00 g

L-lysine……………………………………………..… 10.00 g

Ferric-ammonium citrate………………………..0.50 g

Sodium thiosulphate……………………………… 0.04 g

Bromcresol purple…………………………..………0.02 g

Agar………………………………………………………13.50 g

 

Final pH of the ready to use medium: 6.7 ± 0.2

 

Medium preparation:

Add 34 grams of dehydrated culture medium to 1 litre of distilled water, and allow to soak for 10 minutes. Swirl to mix, then bring to the boil and dispense into tubes. Autoclave at 121°C for 15 minutes. Cooled down the tubes in inclined position to form slants.

 

Quality specifications:

Dehydrated medium: homogeneous, beige coloured, fine powder.

Ready to use medium: purple agar.

 

Microbiological response:

 

Organism Result / lysine decarbox / H2S
Salmonella typhimurium ATCC 14028 Growth,/ + / + , purple and black colour
Shigella flexneri ATCC 12022 Growth / – /- ,yellow-red colour

 

Storage:

Dehydrated medium should be stored between 10 to 25°C. Once opened, place the container in a dark, dry place. The dehydrated medium should not be used if there is any lump or if the colour has changed from the original.