Xylose lysine deoxycholate (XLD) agar is selective for which type of bacteria?

Xylose lysine deoxycholate (XLD) agar is specifically formulated to selectively isolate and differentiate members of the Enterobacteriaceae family from gastrointestinal specimens. This medium is designed to inhibit the growth of non-enteric flora while allowing for the growth of enteric pathogens. The components of XLD agar encourage the fermentation of xylose and lysine, which helps in distinguishing between different types of bacteria based on their metabolic activities.

When Enterobacteriaceae species such as Salmonella and Shigella grow on XLD agar, they can be identified through specific reactions such as hydrogen sulfide production or the inability to ferment xylose completely, leading to characteristic color changes in the medium. This makes XLD agar a valuable tool in clinical microbiology for diagnosing enteric infections. Thus, the correct answer reflects the primary purpose of XLD agar in isolating Enterobacteriaceae from stool cultures, which are commonly associated with gastrointestinal diseases.