(AB) XLD Agar, 500 grams

Modification of medium developed by Taylor XLD Agar has been shown to be superior to other selective media for the isolation of Shigella. Sodium deoxycholate inhibits Gram positive organisms. Xylose is fermented slowly by Shigella and Providencia and thus demonstrate an alkaline reaction (red colonies). Salmonella ferment xylose rapidly but also decarboxylate lysine giving an alkaline reaction. Excess lactose and sucrose prevent lysine positive organisms from reverting to the alkaline reaction. H2S production by Salmonella and Arizona is indicated by black centered red colonies. Sodium thiosulfate is added as the sulfur source and ferric ammonium citrate as indicator. Phenol red is used as an acid-base indicator with lactose and sucrose fermentation giving yellow colonies (acid reaction). Selective and differential medium for the isolation, cultivation and differentiation of enteric bacteria, particularly Shigella sp. from both clinical and non-clinical specimens. (Alpha Biosciences # X24-101-500gm)

Use: Selective and differential medium for the isolation, cultivation and differentiation of enteric bacteria, particularly Shigella sp. from both clinical and non-clinical specimens.

Description: Modification of medium developed by Taylor XLD Agar has been shown to be superior to other selective media for the isolation of Shigella. Sodium deoxycholate inhibits Gram positive organisms. Xylose is fermented slowly by Shigella and Providencia and thus demonstrate an alkaline reaction (red colonies). Salmonella ferment xylose rapidly but also decarboxylate lysine giving an alkaline reaction. Excess lactose and sucrose prevent lysine positive organisms from reverting to the alkaline reaction. H2S production by Salmonella and Arizona is indicated by black centered red colonies. Sodium thiosulfate is added as the sulfur source and ferric ammonium citrate as indicator. Phenol red is used as an acid-base indicator with lactose and sucrose fermentation giving yellow colonies (acid reaction).

Formula* per Liter:

• Yeast Extract .................................... 3.0g
• Lactose ........................................... 7.5g
• Sucrose ............................................ 7.5g
• Xylose ............................................. 3.5g
• L-Lysine ............................................ 5.0g
• Sodium Chloride............................. 5.0g
• Ferric Ammonium Citrate ............... 0.8g
• Phenol Red ................................... 0.08g
• Sodium Deoxycholate ..................... 2.5g
• Sodium Thiosulfate ....................... 6.8g
• Agar .................................................13.5g

Final pH: 7.4 ± 0.2 at 25.0°C

* Grams per liter may be adj. or formula supplemented to obtain desired performance

Preparation: Mix 55 grams of the medium in one Liter of purified water until evenly dispersed. Heat with repeated stirring and boil for one minute to dissolve completely. Distribute and autoclave at 121.0°C for 15 minutes.

Quality Control Specifications:

1. The powder is homogeneous, free flowing and light pinkish-beige.
2. Visually the prepared medium is bright red - reddish orange and clear to trace hazy.
3. Expected cultural response after 18-24 hours at 35.0°C.

Organism                                                                         Result

Escherichia coli ATCC 25922                            Inhibited, Yellow colonies

Salmonella typhimurium ATCC 14028          Red colonies with black centers

Shigella flexneri ATCC 12022                                     Red colonies

Enterococcus faecalis ATCC 29212                        Growth Inhibited

Storage: Store the sealed bottle containing the dehydrated medium at 2 to 30.0°C. Once opened and recapped, place the container in a low humidity environment at the same storage temperature. Protect it from moisture and light. The dehydrated medium should be discarded if it is not free flowing or if the color has changed from the original light pinkish-beige color.