STERLIX® XLD Ready To Use Agar Plate

Product Details
XLD agar (Xylose Lysine Deoxycholate agar) is a selective and differential culture medium commonly used in microbiology laboratories for the isolation and differentiation of Salmonella and Shigella species from clinical and food samples.

The key components of XLD agar include:

Xylose: XLD agar contains xylose as the fermentable carbohydrate. Salmonella species can ferment xylose, leading to acid production and a pH decrease, which is reflected by a color change in the medium.

Lysine: XLD agar contains lysine, an amino acid. Lysine decarboxylase activity is an important characteristic used for differentiating Salmonella and Shigella species.

Deoxycholate: This bile salt compound inhibits the growth of gram-positive bacteria, making XLD agar selective for gram-negative bacteria, including Salmonella and Shigella.

Phenol red: XLD agar contains phenol red, a pH indicator. It turns yellow in the presence of acid produced during carbohydrate fermentation.

In XLD agar, the differentiation of bacterial colonies is based on their ability to ferment xylose and produce specific metabolic byproducts. The typical characteristics observed on XLD agar include:

Salmonella species: These bacteria can ferment xylose, producing acid and turning the agar yellow. Salmonella colonies often appear as black-centered colonies due to the production of hydrogen sulfide (H2S) during the breakdown of cysteine.

Shigella species: Shigella organisms do not ferment xylose, resulting in no acid production. Their colonies appear as colorless or transparent on XLD agar.

Non-pathogenic organisms: Other gram-negative bacteria that can ferment xylose may produce acid and turn the medium yellow. However, they do not produce H2S and do not display black centers like Salmonella.

XLD agar is particularly useful in the detection and isolation of Salmonella and Shigella species, which are significant causes of gastrointestinal infections. The selective and differential properties of XLD agar aid in the identification and differentiation of these pathogens from other enteric bacteria. It is important to note that XLD agar should be used in conjunction with other confirmatory tests to accurately identify and confirm the presence of Salmonella and Shigella species.