Overview
Deoxycholate Agar is a microbiological growth medium developed for the selective isolation and differentiation of enteric pathogens, particularly Salmonella and Shigella species. The medium was first introduced in the early 20th century as an improvement over earlier enteric media. Its selective properties come from sodium deoxycholate, a bile salt that inhibits most Gram-positive bacteria while allowing Gram-negative organisms to grow. The differential aspect of Deoxycholate Agar is based on lactose fermentation. Colonies of lactose-fermenting bacteria appear pink to red, while non-fermenters remain colorless or take on the medium's natural color. This visual distinction makes it valuable for preliminary identification in clinical and food safety testing.
Physical and Chemical Properties
Deoxycholate Agar is typically supplied as a dry powder that requires rehydration and sterilization before use. The complete medium contains peptones as nutrient sources, lactose as the fermentable carbohydrate, sodium deoxycholate as the selective agent, and neutral red as the pH indicator. The pH is adjusted to be slightly alkaline (approximately 7.3-7.5) to favor the growth of enteric pathogens. When prepared, the medium forms a slightly opaque gel with a light pink to tan color. The sodium deoxycholate concentration (typically 0.5-1.0%) is critical - too low reduces selectivity, while too high may inhibit some target organisms. The medium's performance can be affected by the water quality used for preparation, requiring distilled or deionized water for consistent results.
Main Applications
The primary application of Deoxycholate Agar is in clinical microbiology for the isolation of Salmonella and Shigella from stool specimens. Its selective properties help reduce the growth of normal gut flora, making pathogen detection easier. In food microbiology, it's used to test for Salmonella contamination in various products, particularly those where low levels of contamination need to be detected. Environmental testing laboratories use Deoxycholate Agar for water quality monitoring, especially in detecting fecal contamination. Some modified versions exist for specific applications, such as Deoxycholate Citrate Agar for enhanced Salmonella selection. While molecular methods have become more common, this medium remains valuable for initial isolation and culture purposes.
Safety and Storage
The dry powder form of Deoxycholate Agar is generally stable when stored properly, but moisture absorption can compromise its performance. Unopened containers should be kept at 2-8°C and used before the expiration date. Once prepared, the medium should be used within 1-2 days if stored at 2-8°C, as the deoxycholate can degrade over time. Safety precautions are necessary during preparation due to the potential for aerosol formation when handling the powder. Laboratory personnel should wear appropriate personal protective equipment, including masks and gloves. Prepared media containing deoxycholate should be autoclaved before disposal to inactivate any potential pathogens and break down the selective agents.
B2B Procurement Guide
When procuring Deoxycholate Agar in bulk, laboratories should consider several factors. First, verify that the product meets relevant regulatory standards for intended use (clinical, food, or environmental testing). Reputable manufacturers provide certificates of analysis with each batch, including performance testing data. For consistent results, consider establishing long-term relationships with reliable suppliers who can provide batch-to-batch consistency. Bulk purchases (multi-kilogram quantities) typically offer significant cost savings, but ensure adequate storage capacity. Some suppliers offer pre-poured plates, which may be cost-effective for labs with high throughput but limited preparation capabilities. Always confirm shipping conditions to prevent temperature-related degradation during transit.
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