Enteric selection: Intestinal (enteric) bacteria typically grow in the presence of which inhibitory additive, whereas many nonintestinal bacteria are suppressed by it?

Introduction / Context:Selective media exploit physiological differences to favor target organisms. Enteric bacteria are adapted to the gut environment and can tolerate compounds that inhibit nonenteric flora, improving diagnostic recovery.

Given Data / Assumptions:

• We compare additives frequently used in selective media.
• Bile salts are common in enteric-selective formulations.
• Goal: identify the additive that enterics tolerate but others do not.

Concept / Approach:

Bile salts mimic intestinal conditions and are incorporated in media such as MacConkey and SS agars to suppress Gram-positive organisms and many nonenterics while allowing Gram-negative enteric rods to grow. This enhances isolation of pathogens like Salmonella and Shigella from stool specimens.

Step-by-Step Solution:

Verification / Alternative check:

Formulations like MacConkey agar list bile salts among selective agents; growth patterns in labs consistently show enteric Gram-negatives thriving while Gram-positives are inhibited.

Why Other Options Are Wrong:

Low concentration of dyes: while some dyes are selective (e.g., crystal violet), bile salts are the hallmark for enterics.

Sugars and low nitrogen: these are nutrients or conditions, not primary selective inhibitors for enterics.

Common Pitfalls:

Assuming any dye equals enteric selectivity; overlooking that bile salts specifically emulate intestinal bile, a natural barrier many enterics tolerate.

Final Answer:

bile salts